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Rec.Bicycles Frequently Asked Questions Posting Part 3/5

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Archive-name: bicycles-faq/part3

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Subject: 8b.8 Tube and Tire Casing Repair From: John Forester <JForester@cup.portal.com> There sure seems a dearth of knowledge about patching both tubes and casings. Yes, the idea that tubes could be patched without liquid cement was a good idea, but only as an idea to research to see whether an adequate adhesive could be developed. So far as I know, all the peel and stick adhesives are very viscous liquids. That means that they don't harden and therefore that the air pressure will slowly leak into and through them. If the viscosity is high enough it will take the air under pressure a long time to form another leak. A glueless patch of the peel and stick variety cannot have effective solvents in it, because the solvent would evaporate during storage. Even if the patch were sealed inside a container that prevented the evaporation of the solvent, the system would have the problem of getting enough glue onto the tube and then letting the solvent partially evaporate from the open joint for the joint to be made. You might as well use the old system. The problem that some experience is that they find the cement hardened in the zinc dispensing tube. The answer to that is to buy the cement and its solvent in bulk and carry a small quantity in a small jar with a screw cap. A metal jar would be most useful, but I do not know of any common source for such. Small glass jars are commonly available and last well enough. Periodically, examine the cement inside and top up with solvent if it gets too thick. Because the cement tends to glue the cap to the jar, it is desirable to wrap both the jar and the cap with several layers of adhesive tape to provide a better gripping surface at a larger radius. Two kinds of cement are available. The traditional cement is rubber cement, Camel #12-086 Universal Cement, available at tire shops. The other cement is contact cement, available from hardware stores. While the modern formulations often are non-flammable and use chlorinated hydrocarbons as solvents, buy the flammable kind, if available, because the chlorinated hydrocarbons are detrimental to rubber. (Very important for diluting rim cement for tubular tires. Not so important for just tire patches or boots because the solvent evaporates.) In any case, use toluol as the replacement solvent, available at hardware stores. The tube must be cleaned before applying the cement. Stick medium sandpaper to tongue depressors and cut to lengths that fit your patch kit. Cut casings are repaired with an internal boot. Satisfactory boots are made from cotton trouser fabric or from lightweight dacron sail fabric. These must be cemented by contact cement, not tube cement. Cut pieces of suitable size, so that they run almost from bead to bead when laid inside the casing. Coat one side with several layers of contact cement and let it dry completely before storage. Before applying, coat the inside of the casing with contact cement and press the boot into place before the cement dries. Wait about ten minutes before inflating the tire. If you wait too long, the cement really hardens and there will be a narrow spot in the casing because of the greater strength where the patch reinforces the casing. It is probably possible to use contact cement as the tube patch cement. Do not use tube cement for boots; it slowly creeps and allows the boot to bulge. So carry a small jar of each cement, or one of contact cement. Contact cement is suitable for closing the outside of the cut also, but it must be applied in several layers and allowed to dry thoroughly before use, or it will pick up particles from the road. Duro Plastic Rubber is a thicker black rubber paste that can be applied in one layer and left to harden.
Subject: 8b.9 Presta Valve Nuts From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Fri, 07 Nov 1997 16:46:59 PST Jam nuts on Presta valve stems and pumping. 1. The jam nut holds the stem when pumping so that it does not recede into the rim when pressing the pump head against the tire. This is especially useful when the tire is flat (after installing the tube). It also keeps the stem from wiggling around while pumping. Removing the nut should present no difficulty unless the threads have been damaged or the hands are cold. The cold may present a problem, but then just opening the valve nut on a Presta valve under such conditions is difficult. 2. Breaking off stems with a frame pump comes from incorrect pumping. The number of new tubes with broken stems lying along the road proves that this occurs far too often. To avoid breaking the stem, the pump head should be be held in the fist so that the pumping force goes from one hand into the other, not from the pump into the valve stem. To practice the correct action, hold the pump head in one hand with the thumb over the outlet, and pump vigorously letting out no air. All the force goes from one hand into the other. This is essentially what should take place when inflating a tire. It does no good to "get even" with the stupid tube by discarding it on the road for all to see. Most riders understand how to pump a tire and see this only as evidence of incompetence rather than a faulty tube. Besides, this ostentatious behavior constitutes littering for which the the fine in California is $1000. Bike shops should instruct new bike owners about the use of the frame pump. Along with this there should be some tire patch hints like don't try to ride a freshly patched tube, carry a spare tube and always use the spare after patching the punctured tube. Of course this is a whole subject in itself that is also treated in the FAQ.
Subject: 8b.10 Rim Tape Summary From: Ron Larson <lars@craycos.com> This is a summary of the experience of riders on the net regarding various rim tapes, both commercial and improvized. Any additional comments and inputs are welcome. RIM TAPE Rim tape or rim strips are the material that is placed inside a clincher rim to protect the tube from sharp edges of the nipple holes and possibly exposed ends of spokes extending beyond the nipples. Many materials have been used to produce rim tapes: plastic, rubber, tapes consisting of a multi-directional fiber weave, duct tape and fiberglass packing tape. A few factors influence how well a rim tape works. Some of the tapes are available in more than one width. It is important to choose the width that provides the best fit to cover the entire "floor" of the rim as opposed to a tape that is barely wide enough to cover the nipple holes. Another factor is how well the rim tape withstands the stress of being stretched over the nipple holes with a high preassure inner tube applying preassure to it. The main form of failure of the plastic tapes is for the tape to split lengthwise (in the direction the tube lies in the rim) under high preassure forming a sharp edge that the tube squeezes through and then rubs against. Thus the splitting tape causes the flat that it was supposed to be protecting against. REVIEW OF RIM TAPES BY TYPE Plastic Tapes Advantages: Easy to install and remove. No sticky side is involved. Disadvantages: Although there are exceptions, they are prone to splitting under preassure. Michelin Good Experiences: 0 Bad Experiences: 6 Cool Tape Good Experiences: 2 Bad Experiences: 0 Cool Tape is thicker than other plastic tapes and does not exhibit the splitting failure noted above. Hutchinson Good Experiences: 0 Bad Experiences: 2 Specialized Good Experiences: 1 Bad Experiences: 4 Rubber Tapes Advantages: Easy to install and remove. Good if the nipples are even with the rim floor and there are no exposed spoke ends. Disadvantages: Stretch too easily and allow exposed nipple ends to rub through the tape and then through the tape. Rubber strips Good Experiences: 0 Bad Experiences: 2 Cloth tapes woven of multi-directional fibers: Advantages: Easy to install. Do not fail under preassure. Disadvantages: They are a sticky tape and care must be taken not to pick up dirt if they need to be removed and re-installed. Velox Good Experiences:11 Bad Experiences: 0 Velox rim tape comes in three different widths. Be sure to get the widest tape that covers the floor of the rim without extending up the walls of the rim. The stem hole may need to be enlarged to allow the stem to seat properly. Otherwise the stem may push back into the tube under preassure and cause a puncture at the base of the stem. Non-commercial rim tapes Fiberglass packing tape (1 or 2 layers) Advantages: Cheap. Readily available. Easy to install. Disadvantages: Impossible to remove. If access to the nipples is required, the tape must be split and then either removed and replaced or taped over. Fiberglass packing tape Good Experiences: 1 Bad Experiences: 1 Duct tape (hey, someone tried it!!) Advantages: CHEAP. Readily available. Disadvantages: Useless. Becomes a gooey mess that is impossible to remove. Duct tape Good Experiences: 0 Bad Experiences: 1 CONCLUSION While plastic tapes are easy to work with, they often fail. The clear winner in this survey is the Velox woven cloth tape. A quick review of mail order catalogs confirms the experiences of the net. Velox was available in 5 out of 5 catalogs checked. It was the only rim tape available in 3 of the catalogs. The other 2 had one or two plastic tapes available. (None sold duct tape...) One good suggestion was a preassure rating for rim tapes much like the preassure rating of tires.
Subject: 8b.11 Talcum Powder for Tubes and Tires From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Tue, 04 Nov 1997 16:54:17 PST > I've been told since my first bike that I should liberally dust the > tube in talcum powder before installing it. I've believe that this > may have reduced the number of flats I've had recently. Talcum is one of the more durable urban legends. There is no benefit in putting talcum or substitute powder on a tube or in a tire. The practice has come to bicycle tires the same way tire treads that are miniature replicas of automobile treads have... if it's good for cars, it must be good for bicycles. Trucks (and formerly cars) use talcum or graphite powder between tire and tube, because without it, the two can vulcanize from the heat of rolling. This often makes tube removal destructive, leaving tube fragments stuck in the tire casing. Bicycles do not generate enough heat to vulcanize tubes, so they can be removed from the tire without problem. Other than that, talcum has no effect on punctures other than to release air faster when one occurs. A tube stuck to the casing will retain air for a considerable distance after a thorn penetration because the thorn that penetrates plugs the casing hole leaving the tube hole with no outlet. This is especially true for snake bites. I have found such flats the day after when they have gone flat over night. Without powder, a tube will stick adequately to most clincher tires in about 100 miles. Corn starch is no better than talcum powder, the only difference being that it is water soluble, but then who cares. Talcum also cakes up when wet, although it doesn't dissolve. A tube cannot move in a tire when inflated, regardless of what powder is used, because, no translational forces exist, on top of which the holding force between tube and casing is large. That talcum prevents damage when mounting a tire is also not the case, because the pinch occurs when the last part of the bead is being popped onto the rim. This can cause a pinch with or without a tire iron, and powder will not protect a tube from lying in the gap if it hasn't been pushed into the tire adequately. The reason tubes have talcum powder inside is that in manufacture, they become hot enough that, otherwise, they could become inseparably stuck when folded. That is why most butyl tubes have talcum inside.
Subject: 8b.12 ETRTO numbers for tire sizes From: Osman Isvan <osman_isvan@bose.com > There is nothing wrong with tire/rim compatibility. If we...stop calling them with colloquial names such as "26 inch wheel", "road wheel", etc., we would be all set. There is no dimension on a mountain bike rim that is even close to 26 inches. The ETRTO number, bead diameter in millimeters, is *molded* on the sidewall of the tire (to make mislabeling almost impossible) and if it matches, it will match. There is nothing confusing, mysterious or misleading or complicated about the ETRTO designation. The ETRTO designation also includes the width of the tire to be sure it is not too narrow or too wide for the rim, but this dimension is not accurate as it is not critical. Common standard bead diameters are 559 mm (ATB), 571 mm (Triathlon) and 622 mm (road). They are a reasonable size smaller/larger than each other, so what's the problem? The confusion comes from us (marketers and consumers) referring to both the 559 and the 571 standards, and a slew of others, as 26" for some reason. The term "26 inch wheel" refers to the approximate outside diameter of the inflated tire, and has nothing to do with tire/rim compatibility... This is no different with cars, but in automotive "lingo" the colloquial names for wheel sizes are the rim diameter (and that's what matters for compatibility), not the tire outside diameter. The same car comes with either "13 inch" or "14 inch" wheel options but the outside diameter of the tire may be the same. The rubber part takes up the difference. Motorists refer to their RIM SIZE when they talk about wheel diameter. A 13 inch tire such as "175/70 R 13" means it will fit to a 13 inch rim. We should do the same. It is possible to build the same outside diameter by either using a 26 mm wide tire and 559 mm (mountain) rim (ETRTO 26-559) or a 20 mm wide tire on a 571mm (triathlon) rim (ETRTO 20-571), and this doesn't imply they would be interchangeable. And because the 559 mm (Mountain) rims have a diameter of only 22 inches, it takes very fat 2.0 inch (Mountain) tires to bump them up to 26". Of course they wouldn't accept skinny triathlon tires of same thread diameter. When ordering tires, order according to bead diameter (ETRTO designation). This will solve any problems with compatibility. If the salesperson doesn't understand, ask to look for the number which is molded with the casing.
Subject: 8b.13 Tires with smooth tread From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Fri, 05 Dec 1997 16:29:59 PST Drag racers first recognized the traction benefits of slick tires, whose benefit they could readily verify by elapsed times for the standing start quarter mile. In spite of compelling evidence of improved traction, more than twenty years passed before slicks were commonly used for racing cars, and another twenty before they reached racing motorcycles. Today, slicks are used in all weather by most street motorcycles. In spite of this, here at the end of the millennium, 100 years after John Dunlop invented the pneumatic tire for his own bicycle, bicyclists have not yet accepted smooth tread. Commercial aircraft, and especially motorcycles, demonstrate that a round cross section tire, like the bicycle tire, has an ideal shape to prevent hydroplaning. The contact patch, a pointed canoe shape, displaces water exceptionally well. In spite of this, hydroplaning seems to be a primary concern for riders who are afraid to use smooth tires. After assurances from motorcycle and aircraft examples, slipperiness on wet pavement appears as the next hurdle. Benefits of smooth tread are not easily demonstrated because most bicycle riders seldom ride near the limit of traction in either curves or braking. There is no simple measure of elapsed time or lean angle that clearly demonstrates any advantage, partly because skill among riders varies greatly. However, machines that measure traction show that smooth tires corner better on both wet and dry pavement. In such tests, other things being equal, smooth tires achieve greater lean angles while having lower rolling resistance. Tread patterns have no effect on surfaces in which they leave no impression. That is to say, if the road is harder than the tire, a tread pattern does not improve traction. That smooth tires have better dry traction is probably accepted by most bicyclists, but wet pavement still appears to raise doubts even though motorcycles have shown that tread patterns do not improve wet traction. A window-cleaning squeegee demonstrates this effect well. Even with a new sharp edge, it glides effortlessly over wet glass leaving a microscopic layer of water behind to evaporate. On a second swipe, the squeegee sticks to the dry glass. This example should make apparent that the lubricating water layer cannot be removed by tire tread, and that only the micro-grit of the road surface can penetrate this layer to give traction. For this reason, metal plates, paint stripes, and railway tracks are incorrigibly slippery. Besides having better wet and dry traction, smooth tread also has lower rolling resistance, because its rubber does not deform into tread voids. Rubber being essentially incompressible, deforms like a water filled balloon, changing shape, but not volume. For a tire with tread voids, its rubber bulges under load and rebounds with less force than the deforming force. This internal damping causes the energy losses of rolling resistance. In contrast the smooth tread transmits the load to the loss-free pneumatic compliance of the tire. In curves, tread features squirm to allow walking and ultimately, early breakout. This is best demonstrated on knobby MTB tires, some of which track so poorly that they are difficult to ride no-hands. Although knobby wheelbarrow tires serves only to trap dirt, smooth tires may yet be accepted there sooner than for bicycles.
Subject: 8b.14 Rolling resistance of Tires From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Fri, 13 Feb 2004 12:07:59 -0800 The question often arises whether a small cross section tire has lower rolling resistance than a larger one. The answer, as often, is yes and no, because unseen factors come into play. Rolling resistance of a tire arises almost entirely from flexural rubber losses in the tire and tube. Rubber, especially with carbon black, as is commonly used in tires, is a high loss material. On the other hand rubber without carbon black, although having lower losses, wears rapidly and has miserable traction when wet. Besides the tread, the tube of an inflated tire is so firmly pressed against the casing that it, in effect, becomes an integral part of the tire. The tread and the tube together absorb the majority of the energy lost in a rolling tire while the inter-cord binder (usually rubber) comes in far behind. Tread scuffing on the road is even less significant. Patterned treads measurably increase rolling resistance over slicks, because tread rubber bulges and deforms into voids in the tread pattern when the tire bears on the road. This effect, called tread squirm, is mostly absent with smooth tread because tread rubber cannot bulge laterally on road contact because rubber, although elastic, is incompressible. Small cross section tires experience more deformation than a large cross section tires and therefore, should have greater rolling resistance, but they generally do not, because large and small cross section tires are not identical in other respects. Large tires nearly always have thicker tread and often use heavier tubes, besides having thicker casings. For these reasons, smaller tire usually have lower rolling resistance but not from the smaller contact patch to which it is often attributed. These comparative values were measured on various tires over a range of inflation pressures that were used to determine the response to inflation. Cheap heavy tires gave the greatest improvement in rolling resistance with increasing pressure but were never as low as high performance tires. High performance tires with thin sidewalls and high TPI (threads per inch) were low in rolling resistance and improved far less than poorer ones with increasing inflation pressure. As is mentioned in another FAQ item "Mounting Tubular Tires", tubular tires, although having lower tire losses, performed worse than equivalent clincher tires because tubular rim glue absorbs a constant amount of energy regardless of inflation pressure. Only (hard) track glue absolves tubulars of this deficit and should always be used in timed record events.
Subject: 8b.15 Wiping Tires From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Mon, 13 Oct 1997 15:02:23 PDT Although the tire wiping has mostly gone the way of the tubular tire, some riders have remained believers in this practice, that never had any validity in the first place. It is purportedly done to prevent punctures by wiping off glass that may have "stuck" to the tire. If one considers the rotation rate of a wheel in typical bicycling, about 15-20mph, it comes to about 3.5 revolutions per second. When observing a tire wiper, the time between noticing hazardous debris on the road and the first wipe is more than a second. Hence, any glass or other small object would be firmly pressed into the tire by four revolutions and all exposed glass edges chipped off. By the time the other tire is wiped several more seconds will have passed. If the glass is not thoroughly embedded by then it will not enter the tire. This is not to say that particles embedded in a tire always cause a leak immediately, but that they are irrecoverably in the tire at that time. Those who have patched flats from glass will recall that the piece of glass is not easily found, especially if the location of the puncture is not known. The embedded chip is usually imperceptible when wiping the hand over the place even when known. On the other hand, the rear wheel is more subject to flats than the front, because flat objects must first be tipped up to engage a tire to have any effect. Wiping the rear tire on common short frame bicycles is hazardous, because the fingers can be sucked into the narrow gap between tire and seat tube to cause serious injury. Carefully considered, tire wiping is an idle gesture, reassuring to some riders, and impressive to others if deftly executed. I recall as a beginner that learning all the tics of bicycle racing was important. Wiping tires was one of these. Forget it.
Subject: 8b.17 Clinchers vs. Tubulars From: F.J. Brown <F.Brown@massey.ac.nz> D.H.Davis@gdt.bath.ac.uk gave some useful hints on mounting clinchers, mostly involving the use of copious quantities of baby powder, and trying to convince me that clinchers aren't difficult to mount, so ease of mounting isn't a valid reason for preferring tubulars. wernerj@lafcol.lafayette.edu wrote that although average tubulars ride 'nicer' than average clinchers, there are some clinchers around that ride just as 'nice'. He also said that ease of change isn't a good reason for preferring tubulars as if you flat in a race, you're either going to swap a wheel or drop out. He pointed out that tubulars end up costing $20 - $80 per flat. ershc@cunyvm.cuny.edu gave some of the historic reasons that tubulars were preferred: higher pressures, lower weight, stronger, lighter rims. Said that only a few of these still hold true (rim strength/weight, total weight), but he still prefers the 'feel' of tubulars. leka@uhifa.ifa.hawaii.edu started this thread with his observations on clinchers seperated from their rims in the aftermath of a race crash. stek@alcvax.pfc.mit.edu comments on improperly-glued tubulars posing a threat to other racers by rolling off, and noted that this couldn't happen with clinchers. jobst.brandt@stanfordalumni.org agreed with stek, with the additional note that it is inadequate inflation that often allows tubulars to roll. Kevin at Buffalo agreed with stek and jobst about tubulars (improperly or freshly glued) sometimes rolling. ruhtra@turing.toronto.edu says he uses clinchers for cost and convenience. Clinchers let him carry around a tiny patch kit and some tyre irons, costing 60c, whereas tubulars would require him to carry a whole tyre, and would cost more. CONCLUSIONS: THE CLINCHER VS. TUBULAR WAR Tubulars - used to be capable of taking higher pressures, had lower weight and mounted onto stronger, lighter rims than clinchers. Clinchers have now largely caught up, but many cyclists thinking hasn't. Tubular tyre + rim combination still lighter and stronger. - are easier to change than clinchers. This matters more to some people than others - triathletes, mechanical morons and those riding in unsupported races. - cost megabucks if you replace them every time you puncture. ***However*** (and none of the North Americans mentioned this) down here in Kiwiland, we ***always*** repair our punctured tubulars (unless the casing is cut to ribbons). The process doesn't take much imagination, you just unstitch the case, repair the tube in the normal manner using the thinnest patches you can buy, stitch it back up again and (the secret to success) put a drop of Superglue over the hole in the tread. - can roll off if improperly glued or inflated. In this case, you probably deserve what you get. Unfortunately, the riders behind you don't. Clinchers - can be difficult to change (for mechanical morons) and are always slower to change than tubulars. Most people still carry a spare tube and do their repairs when they get home. - are cheaper to run: if you puncture a lot clinchers will probably still save you money over tubulars, even if you repair your tubulars whenever possible. Tubulars are only repairable most of the time, you virtually never write off a clincher casing due to a puncture. - have improved immensely in recent years; top models now inflate to high pressures, and are lighter and stronger than they used to be. Likewise clincher rims. Some debate over whether tubulars are still lighter and tubular rims stronger. Probably depends on quality you select. No doubt that high quality clinchers/rims stronger, lighter and mor dependable than cheap tubular/rim combination.
Subject: 8b.18 Tubular Fables From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Mon, 27 Jan 2003 20:38:07 -0800 (PST) > Why is it better to deflate tubulars between rides or is this just a > silly rumor? Yes and no. The "rumor" arises from a misunderstanding. Track tires, that are most often still tubulars, are generally inflated to more than 10 bar and are dangerous if they were to explode. Good track tires, unlike road tires, are often made of silk with fine and thin strands that are not coated or otherwise protected. I have seen these tires get touched by another rider's pedal and explode, or even when carelessly laid on any angular object, they can burst because only breaking a few cords is enough to start a burst. For this reason track tires are best deflated to less than half their running pressure when not in use. I can still vividly hear the sound of a tire exploding in an indoor track although I heard it only a few times years ago. It is not something you would like to have happen in your car or room. The reasons people give for deflating tubulars are generally false and are given for lack of understanding. This is what makes it sound like an old wive's tale. Most people do it just to be doing what they think is "professional" when in fact the protected sidewalls and pressure of most road tubulars makes deflation as meaningless for them as it is for clinchers. > What advantage is there in aging tubulars? None! The aging concept arose from the same source as the "steel frames need to be replaced because they get soft with age" concept. Both were intended to improve sales during the off (winter) season by bike shops with too much inventory on their shelves. Tires oxidize, outgas, and polymerize from ultraviolet light. The concept of a tire manufacturer making a tire that cannot be used until ripened for six months from the date of purchase is ridiculous. Tires can be made to any specification at the factory. Tires are most flexible and durable when they are new. They don't improve with time and exposure to heat, light, and oxygen or ozone. "Over-aged" tubular tires, have crumbling hard brown latex on their sidewalls that exposes separating cords directly to weather and wear and they have treads crack when flexed. Considering that this is a continuous process, it is hard to explain where, in the time from manufacture to the crumbly condition, the optimum age lies. The claim that tires are lighter after aging is true. Their elastomers have evaporated making the tire brittle and weak. Purchasing tubular tires in advance to age them is unwise, although if there is a supply problem, tubular tires bought in advance should be sealed tightly in airtight bags and kept in the dark, optimally in a freezer. For best results, use new tires because aged tires are only as good as how little they have aged.
Subject: 8b.19 Tubular Tire Repair From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Tue, 04 May 1999 11:07:38 PDT Opening the Tire The tire casing must be opened to gain access to patch the tube. To do this, open the casing by peeling the base tape back and unstitching the seam. If this is a seamless tire, chuck it. There are two types of seams, zipper stitch (using one thread) and two thread stitch. The zipper stitch is identified by having only one thread. It appears to make a pattern of slanted arrows that point in the direction in which it can be 'unzipped'. Never open more tire than is necessary to pull the tube out of the casing. Remember, the tube is elastic and can be pulled a long way from a three cm long opening. Even if there are two punctures not too far apart, the tube can be pulled out of a nearby opening. However, to insert a boot requires an opening of about 6 to 10 cm at the location of the cut or rupture, about the length of the boot (at least 10cm) and a couple of cm more. Base Tape Never cut the base tape because it cannot be butt joined. Always pull it to one side or separate it where it is overlapped. Do not cut the stitching, because it takes more time to pull out the cut thread than to pull it out in one piece. When working on the stem, only unstitch on one side of the stem, preferably the side where machine finished. Use latex to glue down loose threads on a sidewall cut. Paint the exposed casing zone that is to be covered by the base tape and the tape with latex emulsion, allow to partially dry and put the tape in place. Put the tire on a rim and inflate hard. Seam Ripper and Triangular Needle A convenient tool, available in the sewing department at most department and sewing specialty stores is a seam ripper. This and the triangular sewing needle from a Velox patch kit are two highly useful tools for tubular repair, scissors and razor blades being common household items. Zipper Stitch Cut the thread at some convenient place at the upstream end of the intended opening and with a blunt awl, like a knitting needle, pull out several stitches in the direction the stitch pattern points. When enough thread is free to pull on, the stitching can be opened like a zipper. When enough seam is open, thread the loose end through the last loop and pull tight, to lock the zipper. Don't cut off the free end because it is often good enough to re-sew the seam. Two Thread Stitch One of the threads makes a zig zag as it locks the other thread where it penetrates the tire casing. Cut both threads near the middle of the opening and, with a blunt awl like a knitting needle, pull out only the locking thread in both directions, stitch at a time. The locking thread is the one that is easier to pull out. Remove as many stitches as the opening requires. The other thread pulls out like a zipper. Tie a square knot with the loose ends at both ends of the opening and cut off the rest. Patching Patch butyl (black) tubes using patches from a bicycle patch kit. To patch a latex tube, make patches from an old latex tube that are fully rounded and just large enough to cover the hole plus five mm. For instance, a thorn hole takes a 10 mm diameter patch. Use Pastali rim glue (tire patch glue also works but not as well) wiped thinly onto the patch with your finger. Place the patch on the tube immediately and press flat. Latex will pass the volatile solvent allowing the glue to cure rapidly with good adhesion to the tube. Casing Repair Repairing tubular tires requires latex emulsion. You can get it from carpet layers, who usually have it in bulk. You must have a container and beg for a serving. If you are repairing a tubular you probably ride them, and therefore, will have dead ones lying around. The best tubulars generally furnish the best repair material. Most cuts of more than a few cords, like a glass cut, require a structural boot. With thin latex tubes, uncovered casing cuts will soon nibble through the tube and cause another flat. For boot material, pull the tread off a silk sprint tire, unstitch it and cut off the bead at the edge of the fold. Now you have a long ribbon of fine boot material. Cut off a 10cm long piece and trim it to a width that just fits inside the casing of the tire to be booted from inside edge of the bead (the folded part) to the other edge. The boot must be trimmed using a razor blade to a thin feathered edge so that the tube is not exposed to a step at the boot's edge, otherwise this will wear pinholes in a thin latex tube. Apply latex to the cleaner side of the boot and the area inside the tire, preferably so the boot cords are 90 degrees from the facing tire cords. Insert the boot and press it into place, preferably in the natural curve of the tire. This makes the the boot the principal structural support when the tire is again inflated, after the boot cures. If the casing is flat when the boot is glued, it will stretch the casing more than the boot upon inflation. After the boot dries, and this goes rapidly, sew the tire. Valve Stem Replacement This depends on the type of tube. Latex tubes and some of the others have a screwed in stem that has a mushroomed end on the inside and a washer and nut on the outside. These are easily replaced from another tire whose tube is shot. Open the old ruined tire at the stem, loosen the nut, lift the washer and pull out the stem. Open the tire to be repaired on one side of the stem, preferably the side where sewing ended, the messier side, and loosen the base nut, lift the washer, wet the stem at the tube opening with saliva and twist it until it turns freely. Pull it out carefully and insert the replacement stem after wetting its mushroom with saliva. Tire stores have a soapy mixture called "Ru-glide" or the like to do the wetting but it cost a lot more than spit and doesn't work any better. Tube Replacement To replace the entire tube, open the tire on one side of the stem, the side that seems to be easier to re-sew after the repair. Open about eight to ten cm the usual way, so that the old tube can be pulled out by the stem. Cut the tube and attach a strong cord to the loose end of the tube to be pulled through the casing by the old tube as you pull it out. Cut the "new" latex tube about 8-10 cm away from the stem, tie the cord onto the loose end and pull it gently into the casing. Dumping some talc into the casing and putting talc onto the tube helps get the tube into place. With the tube in place, pull enough of it out by stretching it, to splice the ends together. Splicing the Tube This procedure works only with latex tubes. Overlap the tube ends so the free end goes about one cm inside the end with the stem. With the tube overlapped, use a toothpick to wipe Pastali rim cement into the interface. The reason this MUST be done in place is that the solvent will curl the rubber into an unmanageable mess if you try this in free space. Carefully glue the entire circumference and press the joint together by pressing the tube flat in opposing directions. Wait a minute and then gently inflate to check the results. More glue can be inserted if necessary if you do not wait too long. Sewing the Tire Sewing machines make holes through the bead that are straight across at a regular stitch interval. For best results, use the original stitch holes when re-sewing. Use a strong thread (one that you cannot tear by hand) and a (triangular) needle from a Velox tubular patch kit (yes I know they are scarce). Make the first stitch about one stitch behind the last remaining machine stitch and tie it off with a noose knot. With the beads of the tire pressed against each other so that the old holes are exactly aligned, sew using a loop stitch pulling each stitch tight, going forward two holes then back one, forward two, back one, until the seam is closed. This is a balanced stitch that uses one thread and can stretch longitudinally. Gluing Tire to Rim For road tires, that are intended to be manually mounted and replaced on the road, tires with a rubberized base tape are preferred because these are easily and securely mounted by applying a coating of glue to the rim, allowing it to harden and mounting the tire to be inflated hard so that it will sink in and set. Because road tires are intended to be changed on the road, they use a glue that does not completely harden and allows reuse for mounting a spare. Track tires, in contrast can be mounted using hardening glue such as shellac or bicycle tire track glue. This glue is best suited for base tapes that are "dry" cloth. The tire is mounted either with a light coating of track glue on the base tape or un-glued onto a good base of track glue whose last coat is still soft on the rim, into which the tire will set when inflated upon mounting. Hard glue prevents rolling resistance otherwise generated by the gummy road glue. Track glue is primarily useful for record attempts where every effort is needed. Mounting a Tubular The most effective and fastest way to mount a tubular is to place the rim upright on the ground, stem hole up; insert the valve stem of the tire and with both hands stretch the tire with downward force to either side, working the hands downward to the bottom of the rim without allowing the tire to slacken. Try this before applying rim glue on a dry rim and inflate the tire hard so that afterward, mounting is easier on the glued rim. Note that inflation pressure causes the tire to constrict until the cord plies are at about 35 degrees. This effect helps retain the tire on the rim in use. Therefore, do not inflate a tire to mount it. Tubulars should generally not be inflated off a rim because this deforms the tire and base tape adversely, possibly shearing the inter-ply adhesion and loosening the base tape and stitching. Now that you know everything there is to know about this, get some practice. It works, I did it for years.
Subject: 8b.20 Gluing Sew-up Tires From: Roger Marquis <marquis@roble.com> [More up to date copies of Roger's articles can be found at http://www.roble.com/marquis/] Davis criterium, it's hot, hot, hot. The pace is fast and the corners sharp. Inevitably some riders are going to roll tires, happens every year. What can you do to insure that your sew-up tires stay glued when the mercury rises? There is no one cause of poor tire-rim adhesion so let's start at the beginning, new rims and tires. Most rims are shipped with a coating of anti-corrosive substances that closely resemble grease. This has to be thoroughly removed with solvent and a clean rag before you can put down the first coat of glue. Fast Tack is not the best glue to use on a bare rim. Instead try Clement, Wolber or one of the other slower drying glues. Put a thin coat of glue all the way around and leave the wheel(s) to dry for at least 12 hours. While this glue is drying you might check your tires for any latex that might be covering the base tape. If there is any latex at all give it a good roughing up with coarse sandpaper before coating it with a thin layer of standard glue or Fast Tack. This too should be left to dry for a few hours. If you're a light rider or don't plan on doing any hard cornering on hot days you can usually leave out this step but always roughen the latex on the base tape. After the base coat of glue has dried it's time for the adhesive layer. This should be thicker than the first layer but not so thick that it can squeeze out from under the tire when you mount it and get on the rim and sidewalls. If you are using a traditional style road glue let it dry for ten to fifteen minutes before putting your tires on. Tires should be mounted on Fast Tacked rims immediately. New tires usually need a good stretching before they will go onto the rim without tending to roll and get glue all over them. I usually stretch a tire by pulling it around my knees and feet for a few seconds and then mounting it on an old rim for a while. You might want to try mounting the tire on a dry rim first to see just how much stretching it will need. If you used traditional sew-up glue you should wait at least 12 hours before doing any serious cornering. If you need to race right away you can use Fast Tack and corner confidently within an hour. Be sure to spread the glue evenly over the surface of the rim using your finger or a brush. To get the last section of tire onto the rim without making a mess grab the remaining 3 or 4 inches and lift the tire away from and over the rim. This can be difficult if you forget to stretch it beforehand. Some glues work better than others in hot weather. Fast Tack works best followed by Wolber and Vittoria with Clement in the middle and Tubasti at the bottom of the list. When buying Fast Tack be sure you get the real thing. 3-M sells other trim adhesives in boxes nearly identical to Fast Tack. These trim adhesives do not work for bicycle tires! Be careful that whatever glue you do use has not separated in its tube. If it has, take a spoke and stir it up before you squeeze it out. I have also heard of mixing different glues before application. This is a dangerous shortcut that yields unpredictable results. Fast Tack and Clement are the most popular tire adhesives. Even though Fast Tack will dry out you can get a few tire changes between replications if you have a good layer of traditional glue on the rim underneath it. Racing tires though, should be reglued each time. Base tapes can come apart from the tire in hot weather and underinflation can cause tires to roll as well. Check these things as well as the tread for wear or cuts before every race and you'll be able to descend and corner with confidence. Roger Marquis (marquis@roble.com)
Subject: 8b.21 Another way to glue sewup tires From: "Mike & Joanna Brown" <mjbrown1@airmail.net> Date: Wed, 06 May 1998 21:49:53 CDT I have been racing for 6 years now and have tried multiple tire/rim combinations. I have come to the conclusion that good tubular tires on a pair of good carbon fiber rims provide the ultimate ride. But many people dislike tubular tires because of the gluing process and the possibility of rolling the tire during fast cornering. I decided to write this article because of the three to four racers who rolled a tire at the recent Baylor/Mirage sponsored criterium. Rolling a tire at anytime during race can be catastrophic. Everyone has their "best" way of gluing a tire. I can assure you, this is by far the best and SAFEST way to glue a tire to prevent it from rolling during any type of cornering at any speed. I took this process out of Cycling USA last year and now follow it religiously when gluing my own tires. This gluing process was far superior to the manufacturers recommended process in regards to bond strength at tire/rim interface. We will briefly discuss the following; 1) The glue 2) Mounting tubulars to new rims 3) Mounting tubulars to used rims. Not all glues are the same. Especially in Texas! The temperature outside may be 90 to 100 degrees, but the surface you are racing on may be 150 to 160 degrees. You definitely want a glue that sets up hard in hot weather. If not, as the temperature increases the glue/bond gets softer/weaker and chances of roll off and serious injury increase. The article listed seven glues in this order of strongest to weakest tire/rim bond; Vittoria Mastik' One, Continental, Wolbar, SM Fast Track, Vittoria Gutta, Pana Cement and Clement. I prefer clear glues. That way if you screw up its very difficult to tell. With colored glues, if you screw up everyone knows. Also for your information I use Pana Cement. It does not provide the strongest bond, but it sets up perfectly in all extremes of hot weather and it takes one hell of a finger bleeding effort to get the tire off the rim. Gluing tubulars to new rims properly should take about 84 hours. Here's the process. Test mount the tubular to a dry rim, inflate to 100 psi and allow to sit 24 hours. This stretches the tire which will make mounting easier and also allow you to inspect the tube and tire for defects (most "good" tubulars are hand made). After 24 hours remove the tire. Clean the rim with acetone, lacquer thinner or alcohol only. Other types of cleaners may leave a film on the rim that cannot be seen by the eye and will decrease tire/rim bond strength. Composite rim owners should contact the manufacturer for recommended solvents. Roughing the rim surface will not improve the bond strength. Gently scrap the base tape on the tire with a straight edge to remove any latex. If you scrap a one inch section and the appearance of the base tape does not change, then you probably have no latex on the base tape and can stop scrapping. But be sure to visually inspect the entire base tape just to be sure. Inflate your tire off the rim until the base tape rolls outward. Apply a uniform layer of glue over the entire base tape area. It is best to do several tires at this time. You can store those tires not used and anticipate that the adhesive bond will remain strong as long as the tire surface is kept clean. Apply a uniform layer of glue across the entire width of the tire rim gluing surface. The principle bond is at the rim edge; therefore, it is critical for performance to ensure that the glue reaches the edges of the rim. Allow both to dry for 24 hours. Apply an additional coat after that 24 hour period and allow that 2nd coat to dry for 12 hours. Apply a third coat. This is the mounting coat. With Pana Cement, once the third coat is applied to the tire and rim mount the tire immediately. (One tip I would suggest here is before putting glue on the rim is to put black electrical tape on the entire outside edge and breaking surfaces. This makes for very easy cleaning after the tire is put on. Just peal the tape away and all excess glue comes with it and leaves behind a nice, clean breaking surface). Place the rim vertically on a clean, smooth surface with the valve hole at the top of the rim. Place the valve stem through the hole and ensure that it is properly aligned-straight through the hole (Another tip…For those with deep dish rims requiring valve extenders, place a small amount of loctite on the tube valve stem threads and then screw the valve extender on. This will prevent any leaking at that junction once the tire is glued on). Grab the tire 8" away from the valve stem in both directions, pull outward with a mighty heave and place the section of tire between your hands on the rim. Slide your hands down another few inches down the tire, pull and install this section. Once a full 180 degree section of the tire has been mounted, turn the wheel over and place the valve stem section down vertically on the ground. This is the point where I have my wife hold the section of tire I had just put on the rim with two hands at 0 and 180 degrees. I then grab the tire at the top and turn it so the base tape is facing up. At this point I pull up on the tire and roll it onto the top of the rim. It's actually very easy with two people. Once the tire is on the rim, it must be aligned. Inflate the tire to about 50 psi so it can be easily "turned" to align. You can either align the tire by the tread or by the base tape. Here, I prefer to align my tires by the base tape. Higher quality tubulars treads will align properly. Lower quality tires were not necessarily made straight, so perfect alignment may not be possible. Once aligned, inflate the tire to 100 psi and allow to dry for preferably for 24 hours. When gluing tubulars to used rims, do not remove the old tire until you are ready to begin the gluing process as the old tire keeps the rim surface clear of debris which would weaken the new tire joint. You must find a weak point in the joint and begin removing the old tire. On my Zipp 440's, I use a tire lever so I do not damage the rim surface. On aluminum rims you can use a flat head screw driver to make it easier. You may glue a new tire over the old glue on the rim unless it is not contaminated or old, if there is too much glue on the rim or if the remaining glue covers the rim only in spots. If one of these conditions applies to your rim, remove the old glue with heavy duty furniture stripper. Apply the stripper according to the manufactures recommendations. I always put the stripper on and let it sit for 30 to 45 minutes and the old glue then wipes away like butter. DO NOT wipe the glue along the rim. This causes the old glue and stripper to be pushed down into the nipple holes. Wipe across the rim in small sections. Once the rim is free of glue, begin the process as described above in the article. If you leave the old glue on the rim, apply at least one additional coat before installing the tire. To the tire, apply at least one coat and let it dry for 24 hours before putting on the mounting coat. In concluding, let me state once again everyone has their "best" way to mount tubulars. I can honestly say I have mounted and raced on tubulars put on in 24 hours. Those instances are far and few between though. I always make a 100% effort to follow the procedure written above if all possible. 84 hours seems like a long time to wait just to mount a stupid tire. It all comes down to how much you value safety. When it comes to the safety of the other riders, not to mention the consequences of roll off to my wife and my job, I want to be damn sure I'm as safe as I can possibly be because I took the time to do things right!
Subject: 8b.22 Folding a Tubular Tire From: jobst.brandt@stanfordalumni.org (Jobst Brandt) Date: Thu, 08 Aug 1996 15:31:33 PDT Although there are many arcane folds that people devise, it boils down to pragmatism. Most spares are used tubulars because those who use them typically ride together and for a new rider someone offers a spare that gets returned or not at some later time. Therefore, we are talking about a previously glued tubular and the point is to prevent the whole tire from getting goo all over the tread and sidewalls, so you flatten the tire against itself lengthwise with the sticky base tape stuck to the sticky base tape. Now you have about a 40 inch long flat tire that when folded in half twice makes the typical wad that riders carry under their saddles secured by a footstrap. Footstraps being nearly extinct, I don't know what people use today, but whatever it is, it must be tight and secure. If it isn't, the tire will jiggle enough to abrade the sidewalls to become a pre-packaged blowout, to be installed when you get a flat on the road. Don't do it. Most spare bags sold today are not good places to put a tubular tire because they will allow the tire to vibrate too much. It's bad news to ride alone with one spare anyway, so you ought to ride with other tubular riders when you go any significant distance from appropriate tire service. It's not like carrying a tube and patch kit that can go until you run out of patches (you can cut patches in half too). The advantage of using tubulars is so marginal that the little weight saved is best applied to track and criterium racing where its minuscule reduction in rotational inertia can at least be argued to have some significance.
Subject: 8b.23 Coiling a Wire Bead Clincher From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Fri, 17 Oct 1997 10:00:05 PDT _____________ _________ */ \* */ \* */ \* *| |* */ \* *| |* */ \* *| |* *| |* _________*|__________/* *| |* */ *| *| |* *| *| push--> *| pull & turn <-- |* *| *| *| |* *| *| *| |* *\_________*|__________ *| |* *| \* *\ /* *| |* *\ /* *| |* *\ /* *| |* *\_____________/* (*)tread *\_________/* Holding the tire seen edge-on in front of you, pull the front half inward while turning that part so the tread faces you, to make the figure on the right. Fold the side loops over one another on top of the central loop. This is the way band saws are coiled for storage. The three coil pack must be secured to prevent it from springing open again.
Subject: 8b.24 Measuring the circumference of a wheel From: Jobst Brandt <jobst.brandt@stanfordalumni.org> For accuracy, the speedometer wants to know how far the bicycle travels per wheel revolution (under normal load and inflation). Therefore, that is what must be measured, and it is commonly called the "rollout distance". To make this measurement, sit on the bicycle in typical riding position next to a wall for support, and roll forward, starting with the valve stem exactly at the bottom at a mark on the floor. When the stem is again exactly at the bottom, measure the distance traveled. Typically this distance, for a 700-28 tire at 120 lbs pressure, can be as much as 30 mm shorter under load than rolling the unloaded wheel for one revolution.
Subject: 8b.25 What holds the rim off the ground? From: Jobst Brandt <jobst.brandt@stanfordalumni.org> > What forces keep the rim of a wheel with pneumatic tires off the > ground. It obviously can't be the air pressure because that's acting > from top as well as from below. As has been pointed out, the casing walls pull on the rim (or its equivalent) and thereby support the load. The casing leaves the rim at about a 45 degree angle, and being essentially a circular cross section, it is in contact with the rim over its inner quarter circle. At least this is a good representative model. The visualization may be simpler if a tubular tire is considered. It makes no difference whether the tire is held on by glue or is otherwise attaches to the rim such as a clincher is. Either way the tire is attached to the rim, a relatively rigid structure. Under load, in the ground contact zone, the tire bulges so that two effects reduce the downward pull (increase the net upward force) of the casing. First, the most obvious one is that the casing pulls more to the sides than downward (than it did in its unloaded condition); the second is that the side wall tension is reduced. The reduction arises from the relationship that unit casing tension is equivalent to inflation pressure times the radius of curvature divided by pi. As the curvature reduces when the tire bulges out, the casing tension decreases correspondingly. The inflated tire supports the rim primarily by these two effects. Tire pressure changes imperceptibly when the tire is loaded because the volume does not change appreciably. Besides, the volume change is insignificant in small in comparison to the volume change the air has undergone when being compressed into the tire. In that respect, it takes several strokes of a frame pump to increase the pressure of a tire from 100 psi to 101. The air has a low spring constant that acts like a long soft spring that has been preloaded over a long stroke. Small deflections do not change its force materially. For convenience car and truck tires are regularly inflated to their proper pressure before being mounted on the vehicle.
Subject: 8b.26 Making a tubular tire From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Mon, 23 Dec 2002 15:04:39 PST The tedious but simple process of hand made tubulars is not much different from mechanized manufacture that automates many of the steps. Tire casings are made of two crossed layers (plies) of side-by-side cords that are not woven as cloth. An elastic binder between the layers holds them together and for the high quality tubular, that binder is latex rubber. Fabric for tubular is made on a cylindrical drum about 2m long 20cm in diameter, with a narrow 45 degree helical slot from end to end. A single layer of thread (cords) is wound onto the rotating drum from end to end and coated with latex solution. When dry, the unwoven cloth is cut along the 45 degree slot with a razor to produce a 20cm wide sheet (long trapezoid) of diagonal cords lying side-by-side at 45 degrees, held together only by the latex coating. This band, when folded in half lengthwise, with partially cured latex to the inside, will adhere to itself, and make a 10cm wide two ply strip. Both edges of this strip are sheared to a desired casing width. The ends of this cloth band expose single layer triangles that exactly match each other when closed in a loop to make a seamless two ply circular band, the tire casing. An 8mm wide selvage, through which the tire closure seam will be stitched, is folded, glued and sewn along both edges of the casing. A yellow 0.4-0.8mm wall thickness latex tube, much like rubber tourniquets used in blood clinics, is formed into a hoop with a 10mm lap joint. A nickel plated brass Presta valve stem, with a 10mm diameter, rib faced mushroom end, is inserted into a 3mm diameter hole in the tube at its overlap and where it has been reinforced by a 20x40mm elliptical rubber with fabric backing reinforcement that prevents extrusion when the nut is clamped. A rib-faced washer is placed on the protruding stem, secured by a hex nut to produce the air seal. After laying the tube in the casing, a 20mm wide band of soft cloth is sewn to the inside of both edges of the channel shaped casing to prevent the tube from chafing against the main closure seam. The main seam uses one of two common tire stitches. The two thread version appears as an "X" pattern down the middle, while the other uses a single thread diagonal loop and lock (zipper) stitch, both kinds are biased and can change length with the casing. The seam is machine sewn, beginning at the valve stem, and is manually finished when it again reaches the stem. A bias weave base tape with a20-30mm overlap near the position of the stem is placed on a rim and given a coat of latex as is the tire that is mounted on the rim and inflated. The outside of the inflated tire is given a coat latex to which the tread that has also been primed with latex is applied with a little stretch. The tire is complete.
Subject: 8b.27 Things to check after a flat From: Toby Douglass <tdouglas@arm.com> Date: Tue, 13 Jun 2000 14:31:16 +0100 In the last two months I've had a serious spate of rear tube punctures - about twenty and counting now. I wanted to detail some of the things I've learned that aren't in the FAQ. 1. It's important to get your rim tape in *the right way up*. I had a rubber rim tape which had an "up" face and a down face. The down face had two raised edges to help it stay centered in the rim. With the down face "up", the edges cut right into the tube and kept puncturing it. When this happens, the puncture is a thin slit on the underside of the tube. 2. Don't use rubber rim tape for pressures over about 60 psi - it deforms too much and eventually the buldge your tube forms pushing into the spoke hole will rupture - this happened to me. When you examine the tube you'll find little buldges which have permanently deformed the tube over the spoke hole, and one of them will have a fairly large cut in, where the tube ruptured. 3. When you've got a new tyre and you're fitting it and a tube to a wheel, put the tyre onto the wheel a couple of times, using tyre levers (you'll probably have to!) to stretch the tyre a little - it'll help a lot. 4. When you've had a real puncture, and you're found a stone or somesuch which has gone through the tyre, and you're removed the object - *look again*. Sometimes a shard will have seperated from the object proper and will still be in place - when you inflate the tyre and cycle again it'll cause another puncture.
Subject: 8b.28 Mounting Tubular Tires From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Fri, 26 Jan 2001 01:01:01 PST Two kinds of glue are used to secure tubulars to rims, road and track, the latter having become uncommon. Over the years many glues have been available by: d'Alessandro, Clement, Continental, Michelin, Vittoria, Wolber, Pastali, Tubasti, and others. With the decline of tubular use, these brands have become so scarce that riders in the USA turned to other sources, one of which was 3M Fastack (R) that compares favorably with the others and cures faster than most. Road tubulars preferably should have a rubberized base tape, one coated with latex, to improve adhesion to pressure sensitive glues. These glues behave similar to typical sticky tapes, sticking better to slick surfaces than cloth, so that rubberized base tapes stick better to partially dried rim cement than to bare cloth. Do not modify tubular base tape with cleaning solvents because they affect rim cement adversely. Track tubulars, to be glued with hardening adhesive, should have bare cloth base tapes because shellac type track glues adhere poorly to rubberized tape. Hardening glue is used on track tires to avoid rolling losses typical of pressure sensitive rim cements. Because road tires are intended to be changed on the road, their glue must be manually separable and reusable; it must be sticky. However, being gooey, it allows the tire to squirm on the rim, which causes rolling losses independent of inflation pressure. That road tires move on the rim is apparent from the aluminum oxide (dark grey) that invades rim cement during use and cloth textured wear marks from base tape in the rim. Mounting the Tire Stretch the new tubular tire on an old rim, inflate hard and let stand while applying cement to the rim on which the tire is to be mounted. Rim cement dries fairly rapidly, some faster than others. If this is a low viscosity rim glue, it may require more than one coat. Apply additional coats when the previous one has become firm enough to not draw strings when pressing the finger into it. When a good coating (0.5mm) of rim glue has set enough to be firm to the touch, deflate and remove the tire from the stretching rim and mount it on the glued. With the wheel standing upright on the floor, start by inserting the valve stem into the rim and stretch the tire, pulling down with the hands to both sides away from the stem, working around the rim until reaching the bottom with only a short section of tire not yet in place. Lift the wheel and thumb the remaining section onto the rim. Inflate the tire enough for it to take shape, centering it on the rim before inflating hard. Were the glue still soft and mobile, it would get on the sidewalls while mounting the tire. Glue should be firm enough to not make a mess. Because pressure sensitive glues are also thermally sensitive, heat from braking, while descending montians, often melts rim glue enough to make it flow from under the tire in contrast to hard (track) glue. While track glue (Tipo Pista) is more cumbersome to use, it has its benefits for heat but primarily for timed events where fractions of a second make a difference. Mounting track tires is done the same way as with road glue only that it takes several coats of shellac, the last of which must not be allowed to dry, so the bare cloth rim strip will be wet by the glue as the tire is inflated. Mounting the tire cleanly is more difficult and removing the tire sometimes requires tire irons.
Subject: 8b.29 Presta vs Schrader valves From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Thu, 21 Feb 2002 14:42:55 -0800 (PST) Many valve types have come along since the invention of the pneumatic tire but for bicycles mainly Presta and Schrader remain in use. The Presta valve is the more slender of the two and is slightly more cumbersome to use, having a lock nut instead of a spring to ensure closure. However, these two features have kept the Presta valve in use on many bicycles. In the past, sports and racing bicycles used Presta valves because they are slender and enabled racers to inflate tires with a simple pump with attached chuck (pump head) and no hose. Presta valves are easier to pump than Schrader, because they have no valve spring to overcome. Although a valve depressor for Schrader valves could alleviate this, it would require a check valve, impractical to house in lightweight pump heads. The small diameter of the Presta valve requires a smaller hole in the rim, whose size is important for narrow rims where cross sectional strength of is significantly reduced by a stem hole. In narrow rims, clincher tires also leave insufficient space between tire beads for larger Schrader valves. In contrast Schrader valves are more robust, universally used, and have an easily removable core. Spring closure makes them simpler to use because one needs only to press the inflation chuck onto them at an automobile service station. For hand pumps, a screwed or lever chuck provides the valve depressor. The depressor not only makes inflation easier but is necessary to read back pressure in the tire. Although Presta valves have been made with removable cores, demand is so small that they are uncommon. Removable Presta cores can be identified by two wrench flats on the coarse valve cap threads.
Subject: 8b.30 Valve stem separation flats From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Fri, 13 Feb 2004 12:07:59 -0800 A flat caused by valve stem separation, a manufacturing flaw, is less dangerous because it usually becomes apparent during inflation. If it occurs while riding, it causes a slow leak as the vulcanized brass stem gradually separates from the tube. When this occurs, the stem can be pulled out of the tube entirely to leave a small hole into which a valve stem from a latex tube of a tubular tire will fit. Stems from tubulars have a mushroom end, a clamp washer, and a locknut, that fit ideally into the hole left by stem separation. Such a used stem should be part of a tire patch kit. Any good bicycle shop that handles tubular tires or latex tubes should have used ones if they weren't thrown away. In a self accusative manner, riders often place blame for this failure on errant inflation, the use of the anchor nut on the stem, or some other feature of the rim that they failed to ameliorate. On close inspection, separated stems show that the rubber peeled away leaving only a slight black trace on the stem where the leak began. This isn't caused by any of the usually believed mechanisms. It is a manufacturing flaw.
Subject: 8c Tech Wheels
Subject: 8c.1 Stress Relieving Spokes From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Mon, 29 Nov 1999 17:13:28 PST > I wonder if "stress-relieving" is entirely correct? I see it as a > yielding/hardening process, in which the yield load is increased by > embedding the spoke elbow in the hub, bending the elbow to a > different angle, etc. When unloaded from a high load, this area of > the spoke should be more or less elastic. > So I think the term should be "overloading" or "hardening" -- any > thoughts? Yes. It appears that the process of stress relieving is obscure to many if not most people, because after seeming to have made it clear, comments like the above surface. Spokes are cold formed from wire that is (at least DT) as hard and work hardened as it can become. Tensioning does not further harden spokes, there being no plastic deformation. Besides, wire ductility is important in both forming spokes and in use. The coiled wire from which spokes are made is straightened by running it first between rollers staggered in X and then in Y, the wire moving in the Z direction. Reverse bending acts as a degausser, having ever diminishing excursions that affect ever shallower depths of the wire. This stress relieves the wire while removing the curl of being shipped in a coil. If it had no curl, releasing its free end on the spool would allow it to uncoil explosively into a huge birds nest. Wire is cut into suitable lengths, the first operation being to cold form a spoke head onto one end with one axial blow of a die, after which the spoke is cut to a specific length before rolling the thread and bending a 100 degree elbow. Threads, head, and elbow, contain metal that was plastically deformed (beyond yield) as well as metal that was elastically deformed, each having elastic memory. In these transitions, parts that yielded and ones that did not conflict, each wanting to return to or stay in a different shape. This is why a spoke bent by hand springs back only partially when released. On lacing spokes into a wheel, elbows are often additionally bent (brought to yield), thus remaining at or exceeding yield stress during tensioning. Threads also have internal tensile stress besides local compressive stress at the threads. The thread core is already in tension from the lengthening effect of thread rolling and its stress only increases with tensioning. Therefore, spokes in a newly built wheel have locations where stress is near yield, some more so than others. Because fatigue endurance of a metal at or near the yield stress is short, cyclic loads in such spokes will cause failures at high stress points. In normal use, a wheel only unloads spokes, but with spokes near yield, even these stress cycles readily cause fatigue failures. Only the lightest riders on smooth roads might be spared failures with a wheel whose spokes have not been stress relieved. Stress relieving to relax these high stress points is accomplished by over-stressing them in order to erase their memory. It is not done to bed the spokes into the hub, as is often stated. Bedding-in occurs sufficiently from tension. However, stretching spoke pairs with a strong grasp at midspan, can momentarily increased tension by 50% to 100%. Because spokes are usually tensioned no higher than 1/3 their yield stress, this operation has no effect on the spoke as a whole, affecting only the small high stress zones where spokes are near yield. By stretching them, these zones relax below yield by as much as the overload. Stress relieving with a light grasp of spoke pairs is worthless, as is bouncing the wheel or bending it in a partially opened drawer. Pressing axially on the hub, while supporting the rim, requires a force larger than is manually possible but is effective for spoking machines (except the left side rear spokes that would collapse the rim). Another not recommend method, is laying the wheel on the floor and walking on it with tennis shoes, carefully stepping on each pair of crossed spokes. The method works but bends the rim and is difficult to control. It is STRESS RELIEVING! Even though people insist on calling it pre-stressing or seating-in. The wheel is already prestressed when tensioned. Jobst Brandt <jobst.brandt@stanfordalumni.org>
Subject: 8c.2 Anodized vs. Non-anodized Rims From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Mon, 20 Apr 1998 15:31:32 PDT Dark anodized rims were introduced a few years ago as a fashionable alternative to shiny metal finish, possibly as a response to non metallic composites. Some of these rims were touted as HARD anodized implying greater strength. Hard anodizing of aluminum, in contrast to cosmetic anodizing, produces a porous ceramic oxide that forms in the surface of the metal, as much as 1/1000 inch thick, about half below the original surface and half above. It is not thick enough to affect the strength of the rim but because it is so rigid, acts like a thin coat of paint on a rubber band. The paint will crack as the rubber stretches before any load is carried by the rubber. Similarly, anodizing cracks before the aluminum carries any significant load. Rims are made from long straight extrusions that are rolled into helical hoops from which they are cut to length. Rims are often drilled and anodized before being rolled into a hoop and therefore, the anodizing is already crazed when the rim is made. Micro-cracks in thick (hard) anodizing can propagate into the metal as a wheel is loaded with every revolution to cause whole sections of the rim to break out at its spoke sockets. In some rims, whole sidewalls have separated through the hollow chamber so that the spokes remained attached to the inner hoop and the tire on the outer one. In contrast, colored anodizing is generally too thin to initiate cracks. As an example, Mavic MA-2 rims have rarely cracked except on tandems, while the identical MA-40 rims, with a relativley thin anodizing, have cracked often. Anodizing is also a thermal and electrical insulator. Because heat is generated in the brake pads and not the rim, braking energy must flow into the rim to be dissipated to the atmosphere. Anodizing, although relatively thin, impedes this heat transfer and reduces braking efficiency by raising the surface temperature of the brakes. When braking in wet conditions, road grit wears off anodizing on the sidewall, an effect that improves braking. Anodizing is not heat treatment and has no effect on the structural properties of the aluminum.
Subject: 8c.3 Reusing Spokes From: Jobst Brandt <jobst.brandt@stanfordalumni.org> >I just bent my wheel and am probably going to need a new one >built. Can I reuse my old, 3 months, spokes in the new wheel. >The guy at the shop gave me some mumbo jumbo about tensioning or >something. There is no reason why you should not reuse the spokes of your relatively new wheel. The reason a bike shop would not choose to do this is that they do not know the history of your spokes and do not want to risk their work on unknown materials. If you are satisfied that the spokes are good quality you should definitely use them for you new wheel. The spokes should, however, not be removed from the hub because they have all taken a set peculiar to their location, be that inside or outside spokes. The elbows of outside spokes, for instance, have an acute angle while the inside spokes are obtuse. There are a few restrictions to this method, such as that new rim must have the same effective diameter as the old, or the spokes will be the wrong length. The rim should also be the same "handedness" so that the rim holes are offset in the correct direction. This is not a fatal problem because you can advance the rim one hole so that there is a match. The only problem is that the stem will not fall between parallel spokes as it should for pumping convenience. Take a cotton swab and dab a little oil in each spoke socket of the new rim before you begin. Hold the rims side by side so that the stem holes are aligned and note whether the rim holes are staggered in the same way. If not line the rim up so they are. Then unscrew one spoke at a time, put a wipe of oil on the threads and engage it in the new rim. When they are all in the new rim you proceed as you would truing any wheel. Details of this are in a good book on building wheels. The reason you can reuse spokes is that their failure mode is fatigue. There is no other way of causing a fatigue failure than to ride many thousand miles (if your wheel is properly built). A crash does not induce fatigue nor does it even raise tension in spokes unless you get a pedal between them. Unless a spoke has a kink that cannot be straightened by hand, they can all be reused.
Subject: 8c.4 Ideal Wheel Sizes From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Fri, 13 Feb 2004 12:07:59 -0800 > I'm getting a custom frame built and wondered what people thought of > using 26 inch road wheels. Smaller wheels ought to be lighter and > stronger. ...and goes on to list advantages and disadvantages that aren't as clear as the writer assumes. The main reasons for using 700c or 27" wheels, the common sizes for most adult bicycles is better understood by smaller riders who have a hard time fitting these wheels into their smaller bicycle frames. On the other hand, the larger the wheel the better the ride by averaging road roughness. Riders who encounter cattle guards can best explain this. Don't try that with roller blades. Cross sectional area of the rim limits total tension of its spoke complement, whose individual spoke tension limits how much weight the wheel can support. Two to four spokes near the ground contact point of the average wheel support the load at any moment. For this reason, larger wheels would require more spokes that would require a heavier rim to withstand total tension of a greater number of spokes. > It seems to me that the most obvious reason for using 27" wheels is > tradition, but I'm not sure the advantages make it worth trying to > swim upstream. What do you think? Fortunately "standard" wheel size was arrived upon in days when economics played a role and produced a design that optimized many aspects of performance, weight and economy. Hub width was one of these criteria because as the wheel gets larger the hub must become wider to offer reasonable lateral stability. Today much money is spent by people who want the best, or at least better than their peers without consideration of durability and safety. Riders often buy exotic wheels spending more than double than what would serve them best. Most of these wheels offer no advantage other than that a famous racer won a major race on them. If enough riders ask for 24", 25" and 26" wheels, manufacturers will increase prices as their product lines expand, total sales remaining constant. Tires and spokes would follow as a whole range of sizes that were not previously stocked become part of inventory. Meanwhile, bike frames will come in different configurations to take advantage of the special wheel sizes. Sizes whose advantages are imperceptibly small but are touted by riders who talk of seconds saved in their last race or while riding to work. Fat tired wheels generally use 26" rims that give the same outside diameter of the 700c road wheel. The wheel size we ride today was not an idly chosen compromise.
Subject: 8c.5 Tied and Soldered Wheels From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Mon, 16 Dec 1996 15:09:03 PST While writing "the Bicycle Wheel", to conclusively determine what effect tying and soldering of spoke crossings in a wheel had, I asked Wheelsmith to loan me an untied pair of standard 36 spoke rear wheels, on on Campagnolo low and high flange hubs. I had an inner body of a freewheel machined with flats so that a wheel could be clamped into the vise of a Bridgeport milling machine while the left end of its axle was held in the quill. With the hub rigidly secured, with its axle vertical, dial gauges were mounted at four equally spaced locations on the machine bed to measure rim deflections as a 35lb weight was sequentially hung on the wheel at these positions. The deflections were recorded for each location and averaged for each wheel before and after tying and soldering spokes. The wheels were also measured for torsional rigidity in the same fixture, by a wire anchored in the valve hole and wrapped around the rim so that a 35 lb force could be applied tangential to the rim. Dial gauges located at two places 90 degrees apart in the quadrant away from the applied load were used to measure relative rotation between the wheel and hub. Upon repeating the measurements after tying and soldering the spokes, no perceptible change, other than random measurement noise of a few thousandths of an inch, was detected. The spokes were tied and soldered by Wheelsmith who did this as a regular service. The data was collected by an engineer who did not know what I expected to find. I set up the experiment and delivered the wheels.
Subject: 8c.6 Machined rims From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Sun, 26 Jan 2003 19:57:48 -0800 (PST) > Just wondering if it really makes any difference. Some > manufacturers don't even advertise whether the sidewalls are > machined; others do. Velocity for example, makes both, but I > believe they're the same price. What gives? Just marketing hype? What you hear and read is mostly marketing hyperbole, but machining rims has its reason, and it isn't for your benefit. If you inspect a machined rim closely, you'll find a surface that looks as though made by a thread cutting tool. The purpose is not to get a flat braking surface, but rather to produce a series of fine grooves to prevent brake squeal on new bicycle test rides. The machined grooves, about the texture of LP vinyl record grooves, can be felt by running a fingernail across the rim. These fine grooves usually wear off on the first braking descent in wet weather, the condition that causes rim wear in the first place. Even anodizing, which is a hard ceramic, whether thick or thin, is more durable than the machined rim. However, anodizing is not the solution to wear, because it degrades braking. Anodizing being an insulator that overheats brake pads and causes brake fade. The claim that machining is for purposes other than suppressing brake squeal is far fetched. For instance, rim joints have been made with no perceptible discontinuity almost as long as aluminum rims have been made. Unfortunately, some people in marketing believe that rims will separate if not riveted (or welded) and introduced riveting that usually distorts rim joints. Fortunately, that rims were made for many years without rivets and had flawless joints proves otherwise. In practice, machining solves the new-rim squeal problem at the cost of a rim wall of unknown thickness. It also adds a bit of sparkle to the new product by giving rainbow reflections in showrooms. Mavic, for instance, has rims listed as having "CERAMIC2", "SUP, "CD", "UB", MAXTAL", all features that substantially increase cost over plain aluminum rims that were offered at about 1/4 the price not long ago. The web site explains that "CERAMIC2" is an insulator that improves braking even though the rim is "UB" machined, ostensibly for the same purpose, before ceramic coating. This is a tipoff, because without special brake pads, this feature overheats pads causing them to wear rapidly while degrading performance. Not mentioned is that it's main purpose is to reduce rim wear in wet and gritty conditions.
Subject: 8c.7 Wheel Bearing adjustment From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Sun, 23 Mar 2003 12:21:02 -0800 (PST) Bicycle wheel bearings, as most, require a slight preload so that more than one ball under the cone (inner race) will support its load. With proper preload, slight drag should be perceptible. Preload drag is small compared to drag caused by wheel loads, neither of which are significant regardless of adjustment. In contrast bearing life is affected by proper adjustment. Adjusting ball bearings to spin freely unloaded does not reduce operating friction because a bearing with proper preload has lower drag when loaded than one with clearance. For high quality bearings, preload should be just enough to cause light drag when rotating the axle between thumb and forefinger. Low grade bearings will feel slightly lumpy with proper preload. Wheels with quick release (QR) axles present an additional problem in that closing the QR alters bearing clearance. Closing the lever requires increasing manual force with a slight over-center feel near the end of the stroke. This lever force arises from compressing the hollow axle and stretching the skewer. The ratio of elastic length change between axle and skewer is that of their cross sectional area and active lengths. Although small, axle compression on QR hubs is large enough to alter bearing clearance and should be considered when adjusting bearings. Bearings should be adjusted just loose enough so that closing the QR leaves the bearing with a slight preload. Excessive preload from QR closure is the cause of most wheel bearing failures not caused by water intrusion. Clearance, in contrast can be felt as disconcerting rattle when encountering road roughness. To test for proper adjustment, install the wheel and wiggle the rim side-to-side to determine that there is no clearance (rattle), then let the wheel rotate freely to a stop. If the wheel halts with a short (indexed) oscillation, bearing preload is too high. Although adjusting QR force is a safety consideration, it is also one of bearing life. It should be kept at a constant level once the desired closure force has been determined. Rear vertical dropouts require a lower and more predictable closure force than was formerly required with axles that could move forward from chain tension. Because vertical dropouts do not rely on friction to resist chain load, many hubs now have smooth faced jam nuts that do not damage dropout faces as older knurl faced ones did.
Subject: 8c.8 Wheels for Heavy Riders From: pardo@cs.washington.edu Date: Fri, 25 Jul 2003 00:08:48 -0700 Some heavy riders get poor service from mainstream wheels. Common durability problems include wheels that go out of true and broken spokes. Common strength problems include wheel collapse broken rear axles, and broken ratchet mechanism. A ``better'' wheel improves durability and/or strength. Variations in wheel use and budget make it hard to make general recommendations. However, here are some things that can help build a stronger or more durable wheel: - A stiffer rim improves wheel strength and spoke durability by sharing the load among more spokes. Rim stiffness is increased by using a wider rim and is also improved by using a deeper rim. It is clear that a wider rim will build a stronger wheel; however, a deep rim is radially stiffer, which shares the load among more spokes and thus makes the wheel laterally stronger. Thus, using a deep-section rim can improve lateral wheel strength and spoke lifetime, and can also reduce the frequency of wheel re-truing. - All other things equal, a heavy rim is stronger. It is also stiffer, and rim stiffness improves wheel strength. However, rim shape has a dramatic effect on stiffness, and many heavy rims do not have a good shape for building strong or durable wheels. In particular, many heavy rims are not very deep. For many uses, a lighter deep-section rim builds a better wheel than a heavier but shallow rim. - For ``dished'' wheels, use a rim with offset spoke holes. The rim should face so the holes are as close as possible to being centered between the flanges. Although offset rims move the nipple position only a few millimetres, with highly dished wheels the change is a substantial percentage of the dish. Reduced dish improves spoke bracing angles which improves wheel strength; allows higher tension on the low-tension spokes which reduces the rate of re-truing; and may allow higher overall spoke tension, which improves wheel strength. - On front wheels, use hubs with wide flange spacing. Wide-spaced flanges may be as much as 1cm wider than standard flange spacing, and some aerodynamic hubs space the flanges as much as 1cm closer together than standard hubs. Wider flange spacing improves the spoke bracing angle and thus improves lateral wheel strength. It may also reduce the rate at which wheels need to be re-trued. - Center the rear hub by using a narrow sprocket cluster. Wide clusters use space on the right and thus push the flanges to the left; such asymmetry is called ``dish''. Dish hurt the bracing angle of the spokes coming from the flange which is closer to the center line. Dish also forces different left and right spoke tension. The spokes with lower tension are more likely to go slack under load, which weakens the wheel and make truing more frequent. The spokes with higher tension may pull the nipples through the rim before the rim's compressive load strength is reached, thus limiting overall spoke tension for the wheel. Reduced overall spoke tension further weakens the wheel and makes retruing yet more frequent. Narrower clusters reduce dish. As of 2003, Five-sprocket and narrow six clusters are largely unavailable. 6-sprocket and narrow seven clusters are available, but mostly in lower-priced products. Some are good products, but some may be less durable. Eight and nine-sprocket clusters use the same spacing; they get nine in the same space by using thinner material for the sprockets and chain. Nine-speed equipment has a reputation for breaking and may be unsuitable for riders who already have component durability problems. It is sometimes possible to build a 7-speed hub by bolting a replacement 7-speed body on to a new 8-speed hub. Some people retrofit 8 out of 9 sprockets of a 9-speed on to a 7-speed freehub body; but doing so may cause poor reliability due to the thinner sprockets and chains. - Center the rear hub by using a wider dropout spacing. Centering has the benefits listed above. Common dropout spacings range from 120mm to 135mm and some tandems use 140mm and winder. If you have the luxury to select the frame, get a wider spacing, but beware of possible heel clearance and crank width issues with wider spacing. If you have a steel frame it may be possible to spread the stays by 5mm. Beware that spreading requires special tools and skills to avoid frame damage. Aluminum, titainum, and carbon frames cannot typically be spread without damage. Note that simply ``stretching'' the frame to fit over a wider hub may cause gradual frame damage. Spreading the frame requires a longer hub axle. Many hubs are offered in various widths but make sure you have the right parts in hand when the frame is spread. - Use a rear hub with a tandem-rated ratchet mechanism. Many ``racing'' quality hubs are designed for low weight and are no stronger -- and are sometimes weaker -- than mainstream components. - Use a rear hub with an oversize axle. Freewheel hubs are available with steel axles of 17mm. Freehubs are available in two general styles, see the FAQ ``Cassette or Freewheel Hubs'' section. The type labeled Hugi/Campagnolo needs a much larger axle; the type labeled Shimano/SunTour does not need as large an axle. Most modern (2003) freehubs have adequate axles even for heavy riders, but some older ones are inadequate and new designs often bring new weaknesses. - Use a large number of spokes. Most sizes of wheels can be built up to 48 spokes. Note that there is less selection in high-spoke-count hubs and rims, and parts often cost more. The benefit of many spokes is partly limited by the rim strength: a large number of spokes may require lower tension on each spoke to avoid collapsing the rim. Thus, a very strong rim is required to realize the full benefit of using many spokes. - Use high spoke tension. High spoke tension improves radial and lateral wheel strength, improves spoke durability, and reduces the rate at which spokes loosen and let the wheel go out of true. Maximum spoke tension varies from rim to rim and, unfortunately, makers do not typically publish a recommended tension. As of 2003, I have seen only one rim which listed spoke tension. Thus, tension must be discovered in the manner described in _The Bicycle Wheel_ [Brandt]. Although this procedure allows you to set tension for a given rim, it is done as part of building the wheel, which keeps you from choosing rims based on strength. - Stress-relieve the spokes. Spokes are prone to break unless they are stress-relieved after wheel building. Stress-relieving is described in _The Bicycle Wheel_ [Brandt]. Stress relieving is also summarized in the wheels section of the FAQ (``Stress Relieving Spokes''). - Use swaged (``butted''; thinner in the center) spokes. The elbow and threads take high loads and should be of thicker material; the center should be slightly thinner so most stretching takes place in the center section, thus reducing elbow and thread failures. Using swaged spokes also reduces rim cracking at the spoke hole. - Choose spokes according to the type of wheel failure. If spoke or rim eyelet durability is a problem, use lighter spokes. It may seem odd to solve breaking problems by going to a lighter spoke; but spokes are run at 1/2 their yield strength or less, so do not break from overload. Instead, they fail from gradual degradation caused by repeated stretching and relaxing of the metal. Lighter spokes cause the wheel load to be shared among more spokes, reducing the loads on each spoke and thus improving spoke lifetime. A similar mechanism can damage rims at the eylet, and lighter spokes can therefore also help reduce rim damage. Note that using more spokes and a rim with greater radial stiffness also helps spoke and rim bed durability. - If wheel collapse is a problem, use thicker spokes. Note that very thick spokes (2.3mm) will not fit in some hubs. Beware that using thick spokes may hurt spoke and rim bed durability. Note that using more spokes and using a rim with greater radial stiffness and greater lateral strength and stiffness can also reduce wheel collapse. - Use brass (not aluminum) nipples. Aluminum nipples also break more often, especially at high spoke tensions. Brass nipples allow periodic adjustment with less chance of wheel damage. Aluminum nipples tend to sieze and gall. With thse considerations in mind, here are some specific recommendations: (1) Fix the existing wheels. In my experience, most wheels are under-tensioned, even those built by many reputable shops. Many problems with existing wheels can be solved by simply truing the wheel, raising the spoke tension to an appropriate level for the rim, and by stress-relieving the spokes. A conventional wheel can then give good service for many heavy riders. Unfortunately, manufacturers do not rate rims for spoke tension (I have seen only one rim that was marked or rated), so it is necessary to gradually overtension the wheel and then back off, as described in _The Bicycle Wheel_ [Brandt]. Beware that many mechanics are unfamiliar with tensioning and stress relieving procedures, or claim familiarity but do not perform them correctly. Thus, while there are also many mechanics do it right, you cannot assume the mechanics know what they are doing. Familiarize yourself with the tensioning and stress-relieving proeceudres, then interview the mechanic who would repair your wheel, and ask them to explain in detail how they determine proper spoke tension and how they stress-relieve the spokes. If they deviate from the standard procedure, there is a good chance they are missing something important. Note also that a shop or particular mechanic may have a history of satisfied customers and yet still build wheels with low spoke tension and/or improper stress relieving. This can occur because low tension and lack of stress relieving are less important for average riders, so such wheels may not lead to customer returns. (2) Use a deep-section rim. The simplest and probably cheapest change is to use a deep-section rim. Here, ``deep'' means at least 30mm. A deep-section rim allows you to reuse your existing hub and/or buy inexpensive ``mainstream'' hubs, yet a deep-section rim builds a wheel which is dramatically stronger and more durable than a wheel built with a shallower rim. Deep-section rims also give better rim brake cooling, which may be important for heavy riders in hilly areas. Painted rims should be avoided if cooling is a concern; color anodizing does not hurt cooling. Fortunately, deep-section rims are available from several makers in most common sizes (20", 650C, 26", 700C). For dished wheels, given a choice between a deep rim and a rim with offset spoke holes, I do not have data about which is better. My intuition tells me that an off-center rim is probably more imporant the steeper the dish. So, for example, an off-center rim might build a stronger wheel for a 10-speed cluster in a 130mm dropout, while a deep-section rim might build a stronger wheel for an 8-speed cluster in a 135 dropout. (3) Use more spokes; use lightweight spokes. All other things equal more spokes builds a stronger and more durable wheel. However, a deep-section rim is of sufficient benefit that if you are forced to use a shallower rim in order to get more spokes, it may be the same either way. With many spokes (e.g., 48), it is relatively easy to overload the rim while the tension of each spoke is still low. A stiffer rim allows a greater spoke tension, so a deep-section rim still helps to build a strong wheel. Using more spokes allows the use of lighter spokes, which increases spoke and rim bed durability. (4) Avoid ``trendy'' solutions. When discussing strong wheels, special techniques often come up. For example: asymmetrical lacing, straight-pull spokes, paired or crossed spokes, alternative spoke materials, and so on. For any given weight of wheel, these approaches have not demonstrated measurable stiffness or strength benefits in any tests I know of. In addition, they are typically only available in low spoke count wheels anyway. Finally, trendy solutions are typically more expensive. Thus, the best value wheels are typically built using standard components. [Brandt] Jobst Brandt, ``The Bicycle Wheel''. Avocet Press; 3rd edition, October 1998.
Subject: 8d Tech Chains
Subject: 8d.1 Lubricating Chains Lubricating chains is a somewhat religious issue. Some advocate oil, some Teflon-base lubricants, some paraffin wax. The net majority favors a lubricant that does not leave an oily coating on the chain that can attract dirt, which will hasten chain/chainring/freewheel sprocket wear. If you want to use paraffin wax, make sure you melt the wax in a double boiler! Failure to do so can lead to a fire. You can use a coffee can in a pan of boiling water if you don't want to mess up good cookware. After the wax has melted, put the chain in the wax and simmer for 10 minutes or so. Remove the chain, hang it up, and wipe the excess wax off. Let it cool and reinstall on your bike. When using a liquid lubricant, you want to get the lube onto the pins inside the rollers on the chains, not on the outside where it does little good. Oilers with the narrow tubes are good for this because you can put the lube where you want it. Work the oil into the chain after applying it, wipe the chain off, and reinstall on your bike. A good discussion of chain maintenance is at http://www.sheldonbrown.com/chains.html
Subject: 8d.2 Chain cleaning and lubrication; wear and skipping From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Thu, 10 Jan 2002 17:40:52 -0800 (PST) Chain wear and care evokes never ending discussions, especially for new bicyclists who are not happy with this dirtiest of bicycle parts. This leads to the first problem, of whether there is a best (and cleanest) way to care for a chain. There are several ways to take care of a chain of which some traditional methods are the most damaging to the chain and others work to prolong its life. That grease on a new chain, fresh out of the package, is not a lubricant but rather a preservative that must be removed, thrives in bicycling myth and lore. This is nonsense because chains are used as they are by manufacturers who ship bicycles ready to use. They can order chains with any desired lubricant and this is what they use. If there is too much on the chain, it can be wiped off. At the outset the term "chain stretch" is technically wrong and misleading. Chains do not stretch, in the dictionary sense, by elongating the metal through tension. They lengthen because their hinge pins and sleeves wear which is caused almost exclusively by road grit that enters the chain when oiled. Grit sticks to the outside of a chain in the ugly black stuff that can get on ones leg, but external grime has little functional effect, being on the outside where it does the chain no harm. Only when a dirty chain is oiled, or has excessive oil on it, can this grit move inside to causes damage. Commercial abrasive grinding paste is made of oil and silicon dioxide (sand) and silicon carbide (sand). You couldn't do it better if you tried to destroy a chain, than to oil it when dirty. Primitive rule #1: Never oil a chain on the bike. This means the chain should be cleaned of grit before oiling, and because this is practically impossible without submerging the chain in a solvent bath (kerosene or commercial solvent), it must be taken off the bicycle. Devices with rotating brushes, that can be clamped on the chain on the bicycle, do a fair job but are messy and do not prevent fine grit from becoming suspended in the solvent. External brushing or wiping moves grit out of sight, but mainly into the openings in the chain where subsequent oiling will carry it inside. Do not use gasoline because it is explosive and contains toxic light petroleum fractions that penetrate skin. Removing the chain from the bicycle isn't always possible. There are times (after riding in the rain) when a chain screams for oil and good cleaning is impractical. In that case rule #1 may be violated for humanitarian reasons. However, only an internally clean chain squeaks, so it isn't as bad as it sounds. Also, water is a moderately good lubricant, but it evaporates soon after the rain stops. Removing solvent from the chain after rinsing is important. Compressed air is not readily available in the household nor is a centrifuge. Manually slinging the chain around outdoors works best if the chain is a closed loop but without pressing the pin completely in. The other way is to evaporate it. Accelerated drying methods by heating should be avoided, because they can be explosive. Lubricating the chain with hot 90W gear lube works but it is also efficient fly paper, collecting plenty of hardpack between sprockets and on the outside of the chain. Motor oil is far better, but motorcycle chain and chainsaw lubricants are better yet, because they have volatile solvents that allow good penetration for their relatively viscous lubricant. Paraffin (canning wax), although clean, works poorly because it is not mobile and cannot replenish the bearing surfaces once it has been displaced. This becomes apparent with any water that gets on the chain. It immediately squeaks. Swaged bushing chains Sedis was the first with its Sedisport (five element) chain to introduce swaged bushings, formed into the side plates, to replace (six element) chains with full width steel bushings on which the rollers and pins bear. Although stronger and lighter than prior chains, the five element chain achieves its light weight at the expense of durability. These chains, now the only derailleur chains available, have only vestigial sleeves in the form of short collars on the side plates to support the roller on the outside and the link pin on the inside. This design is both lighter and stronger because the side plates need not have the large hole for insertion of sleeves. Pins inside full bushings of (six element) chains were well protected against lubricant depletion because both ends were covered by closely fitting side plates. Some motorcycle chains have O-ring seals at each end. In the swaged bushing design there is no continuous tube because the side plates are formed to support the roller and pin on a collar with a substantial central gap. In the wet, lubricant is quickly washed out of pin and roller and the smaller bearing area of the swaged bushing for the pin and roller easily gall and bind when lubrication fails. Although this is not a problem for this type of chain when dry it has feet of clay in the wet. Chain Life Chain life is almost entirely a cleanliness and lubrication question rather than a load problem. For bicycles the effect of load variations is insignificant compared to the lubricant and grit effects. For example, motorcycle primary chains, operated under oil in clean conditions, last as much as 100,000 miles while exposed rear chains must be replaced often. The best way to determine whether a chain is worn is by measuring its length. A new chain has a half inch pitch with a pin at exactly every half inch. As the pins and sleeves wear, this spacing increases, concentrating more load on the last tooth of engagement, changing the tooth profile. When chain pitch grows over one half percent, it is time for a new chain. At one percent, sprocket wear progresses rapidly because this length change occurs only between pin and sleeve so that it is concentrated on every second pitch; the pitch of the inner link containing the rollers remaining constant. By holding a ruler along the chain on the bicycle, align an inch mark with a pin and see how far off the mark the pin is at twelve inches. An eighth of an inch (0.125) is one percent, twice the sixteenth limit that is a prudent time for a new chain. Skipping Chain Sprockets do not change pitch when they wear, only their tooth form changes. The number of teeth and base circle remain unchanged by normal sprocket wear. A new chain often will not freely engage a worn rear sprocket under load even though it has the same pitch as the chain. This occurs because the previous (worn and elongated) chain formed pockets higher on each tooth (a larger pitch diameter) than an in pitch chain describes. This wear occurs because a worn chain rides high on the teeth. A chain with correct pitch cannot enter the pockets when its previous roller bears the previous tooth, because the pocket has an overhang that prevents entry. Without a strong chain tensioner or a non derailleur bicycle, the chain has insufficient force on its slack run to engage a driven sprocket. In contrast, engagement of a driving sprocket, the crank sprocket, generally succeeds even with substantial tooth wear, because the drive tension forces engagement. However, worn teeth on a driving sprocket cause "chainsuck", the failure of the chain to disengage. This occurs more easily with a long arm derailleur, common to most MTB's, that is one reason this occurs less with road racing bicycles, that experience a noisy disengagement instead. In contrast a worn chain will not run on a new driving sprocket. This is less apparent because new chainwheels are not often used with an old chain. In contrast to a driven (rear) sprocket the chain enters the driving (front) sprocket under tension, where the previous chain links pull it into engagement. However, because a used chain has a longer pitch than the sprocket, previous rollers bear almost no load and allow the incoming chain link to climb the ramp of the tooth, each successive link riding higher than the previous until the chain jumps. The pockets in a used sprocket are small but they change the pressure angle of the teeth enough to cause skipping. Jobst Brandt <jobst.brandt@stanfordalumni.org>
Subject: 8d.3 Adjusting Chain Length From: Bob Fishell <spike@cbnewsd.att.com> For all Shimano SIS and Hyperglide systems, the chain is sized by shifting to the smallest rear cog and the largest front sprocket, then sizing the chain so that the derailleur pulleys are on a vertical line, or as close as you can get to it. Note that this will result in the same chain length for any freewheel within the capacity of the derailleur, so it usually is not necessary to re-size the chain for a different cogset with these systems. The other rule I've used (friction systems) involves shifting to the largest chainring and the largest rear cog, then sizing the chain so that the pulleys are at a 45 degree angle to the ground. The rules probably vary from derailleur to derailleur. In general, you may use the capacity of the rear derailleur cage as a guideline. You want the chain short enough so the cage can take up the slack in the smallest combination of chainwheel and rear cog you will use. The chain must also be long enough so that the cage still has some travel in the largest combination you will use. For example, if you have a 42x52 crank and a 13x21 freewheel, the smallest combination you would use would be a 42/14 (assuming you don't use the diagonal). If the cage can take up the slack in this combo, it's short enough. If the cage has spring left when you are in the 52/19 combo (again, you are not using the diagonal), it's long enough.
Subject: 8d.4 Hyperglide chains For those of you that are tired of dealing with Shimano's chains with the special pins, I've found that the following chains work well with Shimano Hyperglide gearing systems: DID SuperShift Sedis ATB Union 800 Union 915 The SuperShift is probably the best performer of the bunch, followed by the ATB and 915. The 800 doesn't do too well with narrow cogsets (i.e., 8-speeds) because the raised elliptical bumps on the side-plates tend to rub on the adjacent cogs. I've also found that these chains work well on SunTour systems. The 915, however, works better on PowerFlo cogs than it does on regular (AccuShift) cogs (where it tends to slip when shifting).
Subject: 8d.5 SACHS Power-links From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Wed, 12 May 1999 15:38:14 PDT The SACHS Power-link, can be separated easily alone but not when in a chain. The link is designed not to open by axial compression alone, typically when a new chain is used on worn sprockets, where skipping over teeth can cause inertial compression by the trailing chain. To prevent this occurrence, a recess around the head of the stepped pin makes more than a half circle, preventing the pin from sliding in its slot. That means the side plates of the link must be pressed together, taking up side clearance, to raise the head of the sliding pin above this retention. To open the chain, find the link, make an upside down U-shape of the chain with the link as the cross bar, the adjacent chain hanging down, grasp the link diagonally with pliers across the the corners to which the pins are fixed, not the corners with the keyhole slot. Pushing the side plates together assists removal but is not essential, the diagonal force having a lateral compressive component. Before using a Power-link, put it together to see why it does not readily slide from closed to open position. Road grit makes this even more difficult.
Subject: 8d.6 Chain cleaning From: pardo@cs.washington.edu Date: Sat, 26 Jul 2003 09:34:37 -0700 Here is a specific procedure for cleaning a chain. There may be better procedures; please contribute. Note that the best cleaning procedure will vary with the kind of chain lubricant and the riding environment. * Basic Equipment and Procedure I use three jars (old pizza sauce jars) each about a litre labeled ``dirty'' ``clean'', and ``rinse''. The first two are filled with kerosene; the third with paint thinner. I also have an old tin can labeled ``waste'', two solvent-resistant bowls each about two litres (damaged saucepans), an old toothbrush, a paintbrush about 5cm wide, a wooden stick, and a pair of chemical-resistant gloves. I bought about four litres of each solvent and green chemical-resistant gloves at a hardware store for about US$15. The golves keep you from poisoning yourself and also keep your food from tasting like kerosene; I wear them throughout the following procedure. Note that even ``safer'' solvents are easy to set on fire accidentally. Using them in a well-ventilated and/or cold area reduces the hazard. The basic producedure is to wash a chain first in the dirty kerosene, then in the clean kerosene, then in the paint thinner to remove residual kerosene, then air-dry the chain. Kerosene does not evaporate well; if you skip the paint thinner rinse you'll have an oily film of kerosene even if you let the chain dry a long time. When you wash the chain you want to remove the gunk on the outside. You also want to move the chain around a lot in the solvent bath so that you wash out the gunk which is trapped inside. I scrub the outside fairly enthusiastically using the paint brush and toothbrush. I also stir the chain around in the bowl fairly vigorously to clean the inside. I do this in all three solvent baths. I wash the chain in one bowl, then move the chain to the other bowl for the next bath. You could do it all in one bowl if you have someplace for the chain to drip; I had two bowls and it seems to work well. You can reuse the solvents: after use, pour them back in their jars. As the jars sit, after a few weeks most of the grit will settle out at the bottom. Next time you clean your chain, pour most of the solvent in to the bowl, but leave 2mm or so in the bottom above the sludge. With the stick, scrape the sludge on the bottom and swish the jar around to get the gunk in solution in the 2mm of cleaner solvent you left, then pour the gunky solvent in to the ``waste'' can. Don't worry about getting the jar clean, just try to pour out more than half the gunk and you're ahead of the game. Wnen you are done with a solvent bath, just pour it back in the jar. You may find some gunk sitting at the bottom of the bowl. Wipe it out with a discardable rag, newspaper, etc. You lose some solvent each time; the ``dirty'' solvent can be refilled from the ``clean'' solvent so the clean solvent and top off the fresh jar using the jug from the hardware store. I suppose the paint thinner eventually gets diluted with kerosene and won't rinse off the kerosene any more. At that point, pour off some of the ``rinse'' mix in to the ``clean'' jar. When you are done cleaning the chain, put the ``waste'' can someplace well-ventilated where the can won't get knocked over and you won't be bothered by the stink. The solvents will gradually evaporate. That leaves a can of grime, which can be discarded. Note that evaporating organics does pollute; but the total volume is quite small. * Variations Kerosene on the chain will interfere with some lubricants, and kerosene in the chain will prevent other lubricants from being wicked in to the chain as effectively. Hence the paint thinner ``rinse''. It might be as effective to do all cleaining with paint thinner, I have not tried. (The paint thinner was an addition to a routine which was proven to clean the chain but which left a residue.) Diesel is similar to kerosene. I have used bio-diesel to clean parts at a shop with good results. Mineral spirits may be similar to paint thinner and may be cheaper. I have not tried it. Some solvents seem similar to kerosene/thinner but do a poor job. For example, acetone does a poor job of cutting some oils. It's also more toxic and more dangerous than thinner, so don't bother. Gasoline contains more toxic compounds and is much easier to ignite accidentally and thus more dangerous. Even when you wear gloves, the toxic compounds are easy to inhale. Do not use gasoline or other highly-flamable materials to clean your chain; a few dollars of kerosene and paint thinner will last a long time and they are widely available. Dawn Dishwashing liquid can remove some lubricants but in my experience is not good for cleaning chains. Spray-on cleaners may cut grease very effectively. However, many are also more dangerous and more costly than kerosene/thinner. In addition, immersing a chain helps to ``float away'' grit and dilute the grease. The greater the volume of liquid, the more is carried awawy diluted. Spray-on cleaners are a much lower volume and thus can be less effective at floating away grit. Many people use citrus and similar degreasers to clean their chains and report good results. I have had poor results, but do not know why. Beware that some degreasers may not work when diluted with water. I am curious if ``good'' degreasers can be re-used. Citrus degreasers are less flamable and less toxic than kerosene/thinner.
Subject: 8e Tech Frames
Subject: 8e.1 Bike pulls to one side From: Jobst Brandt <jobst.brandt@stanfordalumni.org> For less than million dollar bikes this is easy to fix, whether it corrects the cause or not. If a bike veers to one side when ridden no-hands, it can be corrected by bending the forks to the same side as you must lean to ride straight. This is done by bending the fork blades one at a time, about 3 mm. If more correction is needed, repeat the exercise. The problem is usually in the forks although it is possible for frame misalignment to cause this effect. The kind of frame alignment error that causes this is a head and seat tube not in the same plane. This is not easily measured other than by sighting or on a plane table. The trouble with forks is that they are more difficult to measure even though shops will not admit it. It takes good fixturing to align a fork because a short fork blade can escape detection by most measurement methods. Meanwhile lateral and in-line corrections may seem to produce a straight fork that still pulls to one side. However, the crude guy who uses the method I outlined above will make the bike ride straight without measurement. The only problem with this is that the bike may pull to one side when braking because the fork really isn't straight but is compensated for lateral balance. This problem has mystified more bike shops because they did not recognize the problem. Sequentially brazing or welding fork blades often causes unequal length blades and bike shops usually don't question this dimension. However, in your case I assume the bike once rode straight so something is crooked
Subject: 8e.2 Frame Stiffness From: Bob Bundy <bobb@ico.isc.com> As many of you rec.bicycles readers are aware, there have been occasional, sometimes acrimonious, discussions about how some frames are so much stiffer than others. Cannondale frames seem to take most of the abuse. The litany of complaints about some bike frames is long and includes excessive wheel hop, numb hands, unpleasant ride, broken spokes, pitted headsets, etc. I was complaining to a friend of mine about how there was so much ranting and raving but so little empirical data - to which he replied, "Why don't you stop complaining and do the measurements yourself?". To that, I emitted the fateful words, "Why not, after all, how hard can it be?". Following some consultation with Jobst and a few other friends, I ran the following tests: The following data were collected by measuring the vertical deflection at the seat (ST), bottom bracket (BB) and head tube (HT) as a result of applying 80lb of vertical force. The relative contributions of the tires, wheels, fork, and frame (the diamond portion) were measured using a set of jigs and a dial indicator which was read to the nearest .001 inch. For some of the measures, I applied pressures from 20 to 270 lbs to check for any significant nonlinearity. None was observed. The same set of tires (Continentals) and wheels were used for all measurements. Note that these were measures of in-plane stiffness, which should be related to ride comfort, and not tortional stiffness which is something else entirely. Bikes: TA - 1987 Trek Aluminum 1200, this model has a Vitus front fork, most reviews describe this as being an exceptionally smooth riding bike SS - 1988 Specialized Sirus, steel CrMo frame, described by one review as being stiff, hard riding and responsive DR - 1987 DeRosa, SP/SL tubing, classic Italian road bike RM - 1988 Cannondale aluminum frame with a CrMo fork, some reviewers could not tolerate the rough ride of this bike TA SS DR RM ---------- ---------- ---------- ---------- ST BB HT ST BB HT ST BB HS ST BB HT diamond 1 1 0 2 2 0 2 2 0 1 1 0 fork 3 11 45 3 9 36 4 13 55 3 10 40 wheels 2 2 2 2 2 2 2 2 2 2 2 2 tires 68 52 66 68 52 66 68 52 66 68 52 66 total 74 66 113 75 65 104 76 69 123 74 65 108 What is going on here? I read the bike mags and this net enough to know that people have strong impressions about the things that affect ride comfort. For example, it is common to hear people talk about rim types (aero vs. non-aero), spoke size, butting and spoke patterns and how they affect ride. Yet the data presented here indicate, just a Jobst predicted, that any variation in these factors will essentially be undetectable to the rider. Similarly, one hears the same kind of talk about frames, namely, that frame material X gives a better ride than frame material Y, that butted tubing gives a better ride that non-butted, etc. (I may have even made such statements myself at some time.) Yet, again, the data suggest that these differences are small and, perhaps, even undetectable. I offer two explanations for this variation between the data and subjective reports of ride quality. Engineering: These data are all static measurements and perhaps only applicable at the end of the frequency spectrum. Factors such as frequency response, and damping might be significant factors in rider comfort. Psychology: There is no doubt that these bikes all look very different, especially the Cannondale. They even sound different while riding over rough roads. These factors, along with the impressions of friends and reviews in bike magazines may lead us to perceive differences where they, in fact, do not exist. Being a psychologist, I am naturally inclined toward the psychological explanation. I just can't see how the diamond part of the frame contributes in any significant way to the comfort of a bike. The damping of the frame should be irrelevant since it doesn't flex enough that there is any motion to actually dampen. That the frame would become flexible at some important range of the frequency spectrum doesn't seem likely either. On the other hand, there is plenty of evidence that people are often very poor judges of their physical environment. They often see relationships where they don't exist and mis-attribute other relationships. For example, peoples' judgement of ride quality in automobiles is more related to the sounds inside the automobile than the ride itself. The only way to get a good correlation between accelerometers attached to the car seat and the rider's estimates of ride quality is to blindfold and deafen the rider (not permanently!). This is only one of many examples of mis- attribution. The role of expectation is even more powerful. (Some even claim that whole areas of medicine are built around it - but that is another story entirely.) People hear that Cannondales are stiff and, let's face it, they certainly *look* stiff. Add to that the fact that Cannondales sound different while going over rough roads and perhaps the rider has an auditory confirmation of what is already believed to be true. Unless anyone can come up with a better explanation, I will remain convinced that differences in ride quality among frames are more a matter of perception than of actual physical differences.
Subject: 8e.3 Frame repair From: David Keppel <pardo@cs.washington.edu> (Disclaimer: my opinions do creep in from time to time!) When frames fail due to manufacturing defects they are usually replaced under warranty. When they fail due to accident or abuse (gee, I don't know *why* it broke when I rode off that last motorcycle jump, it's never broken when I rode it off it before!) you are left with a crippled or unridable bike. There are various kinds of frame damage that can be repaired. The major issues are (a) figuring out whether it's repairable (b) who can do it and (c) whether it's worth doing (sometimes repairs just aren't worth it). Kinds of repairs: Bent or cracked frame tubes, failed joints, bent or missing braze-on brackets, bent derailleur hangars, bent or broken brake mounts, bent forks, etc. A frame can also be bent out of alignment without any visible damage; try sighting from the back wheel to the front, and if the front wheel hits the ground to one side of the back wheel's plane (when the front wheel is pointing straight ahead), then the frame is probably out of alignment. * Can it be repaired? Just about any damage to a steel frame can be repaired. Almost any damage to an aluminum or carbon fiber frame is impossible to repair. Titanium frames can be repaired but only by the gods. Some frames are composites of steel and other materials (e.g., the Raleigh Technium). Sometimes damage to steel parts cannot be repaired because repairs would affect the non-steel parts. Owners of non-steel frames can take heart: non-steel frames can resist some kinds of damage more effectively than steel frames, and may thus be less likely to be damaged. Some frames come with e.g., replacable derailleur hangers (whether you can *get* a replacement is a different issue, though). Also, many non-steel frames have steel forks and any part of a steel fork can be repaired. Note: For metal frames, minor dents away from joints can generally be ignored. Deep gouges, nicks, and cuts in any frame may lead to eventual failure. With steel, the failure is generally gradual. With aluminum the failure is sometimes sudden. Summary: if it is steel, yes it can be repaired. If it isn't steel, no, it can't be repaired. * Who can do it? Bent derailleur hangers can be straightened. Indexed shifting systems are far more sensitive to alignment than non-indexed. Clamp an adjustable wrench over the bent hanger and yield the hanger gently. Leave the wheel bolted in place so that the derailleur hanger is bent and not the back of the dropout. Go slowly and try not to overshoot. The goal is to have the face of the hanger in-plane with the bike's plane of symmetry. Just about any other repair requires the help of a shop that builds frames since few other shops invest in frame tools. If you can find a shop that's been around for a while, though, they may also have some frame tools. * Is it worth it? The price of the repair should be balanced with * The value of the bicycle * What happens if you don't do anything about the damage * What would a new bike cost * What would a new frame cost * What would a used bike cost * What would a used frame cost * What is the personal attachment If you are sentimentally attached to a frame, then almost any repair is worth it. If you are not particularly attached to the frame, then you should evaluate the condition of the components on the rest of the bicycle. It may be cheaper to purchase a new or used frame or even purchase a whole used bike and select the best components from each. For example, my most recent reconstruction looked like: * Bike's estimated value: $300 * Do nothing about damage: unridable * Cost of new bike: $400 * Cost of new frame: $250+ * Cost of used bike: $200+ * Cost of used frame: N/A * Cost of repair: $100+ * Personal attachment: zip Getting the bike on the road again was not a big deal: I have lots of other bikes, but I *wanted* to have a commuter bike. Since I didn't *need* it, though, I could afford to wait a long time for repairs. The cost of a new bike was more than I cared to spend. It is hard to get a replacement frame for a low-cost bicycle. I did a good bit of shopping around and the lowest-cost new frame that I could find was $250, save a low-quality frame in the bargain basement that I didn't want. Used frames were basically the same story: people generally only sell frames when they are high-quality frames. Because the bike was a road bike, I could have purchased a used bike fairly cheaply; had the bike been a fat-tire bike, it would have been difficult to find a replacement. The cost of the frame repair included only a quick ``rattlecan'' spray, so the result was aesthetically unappealing and also more fragile. For a commuter bike, though, aesthetics are secondary, so I went with repair. There is also a risk that the `fixed' frame will be damaged. I had a frame crack when it was straightened. I could have had the tube replaced, but at much greater expense. The shop had made a point that the frame was damaged enough that it might crack during repair and charged me 1/2. I was able to have the crack repaired and I still ride the bike, but could have been left both out the money and without a ridable frame. * Summary Damaged steel frames can always be repaired, but if the damage is severe, be sure to check your other options. If the bicycle isn't steel, then it probably can't be repaired.
Subject: 8e.4 Frame Fatigue From: John Unger <junger@rsg1.er.usgs.gov> I think that some of the confusion (and heat...) on this subject arises because people misunderstand the term fatigue and equate it with some sort of "work hardening" phenomena. By definition, metal fatigue and subsequent fatique failure are well-studied phenomena that occur when metal (steel, aluminum, etc.) is subjected to repeated stresses within the _elastic_ range of its deformation. Elastic deformation is defined as deformation that results in no permanent change in shape after the stess is removed. Example: your forks "flexing" as the bike rolls over a cobblestone street. (an aside... The big difference between steel and aluminum as a material for bicycles or anything similar is that you can design the tubes in a steel frame so that they will NEVER fail in fatigue. On the other hand, no matter how over-designed an aluminum frame is, it always has some threshold in fatigue cycles beyond which it will fail.) This constant flexing of a steel frame that occurs within the elastic range of deformation must not be confused with the permanent deformation that happens when the steel is stressed beyond its elastic limit, (e. g., a bent fork). Repeated permanent deformation to steel or to any other metal changes its strength characteristics markedly (try the old "bend a paper clip back and forth until it breaks" trick). Because non-destructive bicycle riding almost always limits the stresses on a frame to the elastic range of deformation, you don't have to worry about a steel frame "wearing out" over time. I'm sorry if all of this is old stuff to the majority of this newsgroup's readers; I just joined a few months ago. I can understand why Jobst might be weary about discussing this subject; I can remember talking about it on rides with him 20 years ago....
Subject: 8e.5 Frames "going soft" From: jobst.brandt@stanfordalumni.org (Jobst Brandt) Date: Mon, 20 Apr 1998 15:31:32 PDT > I have read accounts of "frames going dead" in cycling literature in > the past. If you have information that debunks this, I'd like to > know about it. The explanations I have read claim that the flexing > of a metal causes it to heat up and harden, making it more brittle. > Eventually it will break under stress. In fact, I read recently > that aluminum frames are coming out with warning stickers stating > "this frame will break someday". I have also read that this happens > to titanium and steel. It was in print, therefore it is true! Also known, is that a freshly washed and polished car runs better. Just the idea that the car is admirably clean makes this concept appear true for many drivers. The same psychosomatic mechanism is at work when a bicycle racer thinks it is time for a new frame. I even suspect that some frame builders assisted in spreading this idea to improve frame sales. Metal fatigue and failure occur, but they do not change the elastic response of the metal. Steel (and of course aluminum and other common metals) have been metallurgically characterized over more than a century to a precise understanding. None of this research has shown the possibility of perceptible change in elastic response from any stresses to which a bicycle frame might be subjected. You mention brittleness. Brittleness describes the failure mode of a material and is not a perceptible unless the material breaks. Hardness is also not perceptible unless you exceed the elastic limit and permanently bend the frame, exposing the metal's yield point, the point at which it no longer rebounds. If not, it springs back unchanged as do most ceramics such as a dish, or a glass that is dropped without breaking. If it breaks, it does not bend and none of the shards show any distortion. It either breaks or it doesn't. That's brittleness personified. What escapes the believers of material change is that neither "softening" or "hardening" effects the elastic modulus of the metal. A coat hanger and a highspeed steel drill of the same diameter have the same elastic bending stiffness. For small bending deflections, both are equally stiff, although the hardened steel can bend farther than the soft steel and still spring back unchanged. The stress at which it permanently deforms is the measure of "hardness" of the metal, not its elasticity. Classically, when bicycle parts or frames fail, the rider usually notices nothing before hand. This is true for most thick cross section parts and often even frame tubes frames. The reason for this, is that to permit any perceptible change in deflection, all the added elasticity must come from a crack that has practically no volume. So the crack would need to open substantially to, by itself, allow perceptible motion. Since this is not possible without complete failure, the crack grows in length, but not width, until the remaining cross section can no longer support the load, at which time it separates. > If these ideas have been widely disproven, I'd appreciate knowing > how. I've read all six parts of the FAQ and did not see it mentioned. The reason this was not in the FAQ may be that the whole subject is so preposterous to engineers, metallurgists, and physicists, that they, the people who might explain it, are generally not inclined to bother discussing whether "the moon is made of green cheese" or not. > PS. If what you're objecting to is the use of the word "dead" as > opposed to brittle and inflexible, I'll grant you that. The objection is that you present something for which there is no iota of scientific evidence, nor any even slightly credible explanation, as though it were fact. It is as though bicyclists have a different natural world, where the technical laws are entirely different from all other machinery, and the most perceptive technical insights come from the strongest bicycle racers. "After all who knows more about bicycles, you or the world champion?" is a common retort. Jobst Brandt <jobst.brandt@stanfordalumni.org>
Subject: 8e.6 Inspecting your bike for potential failures From: richkatz@cruzio.com (Keith Bontrager) Handlebars are probably the one component that deserves the most respect. Easton recommends a new bar every two years. I don;t recall if they include an "if you race" preface. I'd say that's probably about right. Same for our aluminum bars. Yearly would be good on bars that have not been engineered for extended fatigue lives. Of course, if you don;t race, if you have more than one bike, if you are a smooth rider, if you like to do "skyshots" you need to work this in to the estimate. Getting tougher, eh? Many people could ride on the good quality bars into the next millenium without a problem. How do you sort it out? I don't know. Many parts (not bars or forks) will give you ample warning if you bother to inspect your bike regularly. Clean it. Look at it. There are "hot spots" all over the bike that deserve carefull attention. Fork crown. Welds if a rigid fork, crown material if its a sus fork. Steerer. Hard to look at, but once a year, especially if it's aluminum or if you've crashed hard with a big front impact. Also if there are noises from the front of the bike when you climb or sprint, or if the bike starts handling funny. Be careful when you change lower head set races so you don't gouge up the steerer at the bottom. If you have an AHS stem/steerer look at the steerer at the point where the stem and HS bearings meet. Critical! Stem. All of the welds and the binder. Especially if you are a 200lb sprint specialist. Down tube/head tube joint of the frame - underneath. Top tube/ head tube joint - same location. Seat tube - near the BB shell and near the seat binder clamp slot. BB spindle. Hard to look at, but once a year. Look near the tapers where the crank fits on. This is the weak spot. If the crank feels funny when you are pedaling (hard to describe the feeling) or if it comes loose unexpectedly, look long and hard at the spindle. Cartridge BBs that allow you to change the bearings should be treated with some respect. You can keep fresh bearings in them forever, guaranteeing that they'll be in service until the spindle fails! Cranks. Check the right hand arm all around where the arm leaves the spider. Also check the hub where the arm attaches to the spindle - especially if the arm is machined from bar (CNC). The section near the pedal threads was prone to failure on older road cranks though I have not seen this on MTB cranks (yet!). Look all over the arms on the light aftermarket cranks. Often. Twice. Seat post. Pull it out and sight down the quill. Any ripples or deformation around the area where the post is clamped in the frame indicates a failure on the way. The clamps are too varied to comment on. If you have to run the fasteners real tight to keep the saddle from slipping you should put new, very high strength fasteners in every year or so. The clamps can come loose from the quill tube sometimes (ask me how I know). Grab the saddle and give it a twist. Saddle. Rails near the seat post support pieces. Rims. material around spoke holes can pull out, side walls can wear through, side walls can fail due to extrusion defects. Some of these are hard to see. Frames around the dropouts (not a problem with newer frames as it was with older campy forged drops). Chainstays near the CS bridge and BB shell. Hubs. Flanges can pull away from the hub body. Not a problem in most cases unless the wheels are poorly built, you are running radial spokes and ride real hard, have poorly designed aftermarket hubs, or are very unlucky. Many components will make a bit of noise or make the bike feel funny before they go. Not all will. Respect this.
Subject: 8e.7 Frame materials From: Sheldon Brown <CaptBike@sheldonbrown.com> Date: Mon, 27 Nov 2000 04:10:19 GMT See http://sheldonbrown.com/frame-materials.html
Subject: 8e.8 Bottom Bracket Drop From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Mon, 10 Jul 2000 16:09:46 PDT I'm not familiar with BB drop. How is it measured and what are its limits? For road bicycles, using conventional sized wheels, BB drop (BB spindle centerline below wheel axle centerlines) has been empirically arrived upon at about [240mm minus crank length] for useful cornering clearance. Imbalance of pedaling in curves at greater lean causes side-slip. For this reason, higher BB's have shown no advantage in criterium racing while road races are practically unaffected by maximum cornering ability while pedaling. Track bicycles have certain advantages on tracks with low banking if they can ride the curves at zero speed but then that depends on track length and how it is banked.
Subject: 8e.9 Bent Frames From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Wed, 03 Jan 2001 16:50:20 PST How to determine whether a frame is straight after a crash and what can be done about it. First is visual, especially for head-on collisions on a standard steel frame, on which top and down tubes generally bend at the end of their butted section, about 50-100mm from the head tube. This usually causes cracks in the paint and can be detected by laying a straight edge on the down tube. Next, sight down the fork to determine if the fork blades are straight in the fore and aft plane, and whether their upper straight portion is parallel to head tube. Bicycles with straight blade forks (with angled crown) make the latter impossible. Another simple test is to ride no-hands and see whether the bicycle rides straight. This will show whether the fork is laterally correct. Determining whether the "rear triangle" is displaced requires measurement. The rear triangle, actually a tetrahedron (four sided figure with six edges), is not easily bent except by side force on the BB. Tubes bent by a force at midspan are self evident by no longer being straight. Bicycles with curved stays are on their own here, having no credible reason for their curvature, which becomes apparent when trying to determine whether they are "straight." Rear triangle displacement is measured by stretching a string from one dropout over the head tube back to the same place on the opposite dropout. The distance between string and seat tube should be identical for both sides. Also, because the two sides of a frame are seldom identically strong, dropout spacing will most likely not be correct, one side having yielded differently than the other. Such lateral displacements can be manually corrected by laying the frame on its side, placing the foot on the inside of the lower chainstay at the BB and pulling the dropout of the upper side toward the correct position. Monitor position change by measuring dropout spacing. After advancing a few millimeters, put the foot on top of the upper chainstay at the BB and pull the lower dropout until the spacing is correct and repeat the sting measurement. Laterally correcting a front fork is done similarly while monitoring dropout spacing. Here the critical test is whether the bicycle rides no-hands straight, which is relatively easy considering that the only the wheel need be removed to perform the bend. Otherwise, sighting down the head tube onto a dummy axle with a centerline on it can help determine whether the fork is "on axis." Forks are best straightened with fixturing but can be done without. For steel frames, these operations pose no problem if the distortion is within limits that do not peel off paint. Frames with oversized tubes generally make their fatal bends self evident by wrinkling as do downtubes of standard steel frames in head-on collisions.
Subject: 8e.10 Aligning a Fork From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Fri, 11 May 2001 16:35:42 PDT aka Bicycle pulls to one side Riders occasionally complain that their bicycle pulls to one side when ridden no-hands. That is, the rider must lean off to one side to ride straight ahead. This symptom can be from a wheel that is in crocked, something that is easily checked by observing whether the tire is centered under the brake bolt, or by just reversing the wheel to see if the wheel is improperly centered. Assuming the bicycle still pulls to one side, the reason is usually that the fork is bent from a side impact. Bent from a frontal impact this is easily seen because the blades have a rearward bend just below the fork crown where the blades should be straight both fore and aft and side to side. A frontal bend usually gives a side bend because the blades are not identical and tend to skew to one side. This is harder to fix and requires fixturing. If the fork is only bent to the side, the correction must be to the side to which the rider must lean when riding no-hands. This bend can be done carefully by bending one blade at a time. Lay the bicycle on its side, front wheel removed. Place the rubber soled foot inside the crown of the fork and pull the upper blade until the gap at the fork end increases by a couple of millimeters. This should be measured. With the foot in the same place pull the other fork blade until the original spacing is restored. Ride the bicycle and assess the difference. Repeat if necessary. This must be done with a strong arm and a bit of skill but it is simple. If you have a non steel bicycle, buy a new fork.
Subject: 8e.11 Stuck Handlebar Stem From: Jobst Brandt <jobst.brandt@stanfordalumni.org> Date: Fri, 11 May 2001 16:35:42 PDT Frozen aluminum stems were a common occurrence because conventional stems were poorly anchored in the fork, having only an expander at the bottom and the top free to pump from side to side with handlebar forces. This was OK in the days of steel stems and steel steer tubes but aluminum accelerated corrosion in this interface, expanding greatly with oxidation, in spite of grease in the interface that only turns to an emulsion in the rain from lateral pumping action. The expander bolt must be backed off about 1/2 inch to hammer the expander wedge out of engagement with the bottom of the stem. When the expander is free, the bolt should be loose with the expander dangling on its other end down in the steer tube. Now the stem should be rotatable with moderate force. If this is not the case, then it is a corroded frozen stem. Many forks have been damaged by twisting the bars forcefully in an attempt to free the stem. Don't do it. Pouring ammonia onto the gap is ineffective unless the stem is not truly frozen. The thin oxide interface to be dissolved is thousands of times as deep as thick. There being no circulation, this method works only in abstract theory. A skilled mechanic can saw off and drill the stem out until it is a thin shell, then break through one side of the shell with a grinder to extract the stem. Because aluminum corrosion expands enough to stretch the steel steer tube, it cannot be loosened by force. Riders often are happy when their stem stops creaking only to find later why it got quiet. It was no longer removable. The main advance achieved by threadless head bearings is that the stem is no longer subject to this failure. It is more a stem improvement than a head bearing improvement, although it also makes adjustment simpler and less expensive. Get it removed by a competent shop. Frame builders do this regularly.
Subject: 8f Tech Moving Parts
Subject: 8f.1 SIS Adjustment Procedure From: Bob Fishell <spike@cbnewsd.att.com> Shimano's instructions for adjusting SIS drivetrains varies from series to series. The following method, however, works for each of mine (600EX, 105, and Deore'). [Ed note: Works on Exage road and mtb also.] Your chain and cogs must be in good shape, and the cable must be free of kinks, slips, and binds. The outer cable should have a liner. clean and lubricate all points where the cable contacts anything. SIS adjustment: 1) Shift the chain onto the largest chainwheel and the smallest cog, e.g., 52 and 13. 2) WITHOUT TURNING THE CRANKS, move the shift lever back until it clicks, and LET GO. This is the trick to adjusting SIS. 3) Turn the crank. If the chain does not move crisply onto the next inside cog, shift it back where you started, turn the SIS barrel adjuster (on the back of the rear derailleur) one-half turn CCW, and go back to step 2. Repeat for each pair of cogs in turn until you can downshift through the entire range of the large chainwheel gears without the chain hesitating. If you have just installed or reinstalled a shift cable, you may need to do this several times. 4) Move the chain to the small chainring (middle on a triple) and the largest cog. 5) turn the cranks and upshift. If the chain does not move crisply from the first to the second cog, turn the SIS barrel adjuster one-quarter turn CW. If the drivetrain cannot be tuned to noiseless and trouble-free SIS operation by this method, you may have worn cogs, worn chain, or a worn, damaged, or obstructed shift cable. Replace as needed and repeat the adjustment.
Subject: 8f.2 SIS Cable Info From: Jobst Brandt <jobst.brandt@stanfordalumni.org> After Joe Gorin described the SIS "non-compressive" cable housing to me I got myself a sample to understand what the difference is. I believe "non-compressive" is a misnomer. This cable housing is NOT non-compressive but rather a constant length housing. As far as I can determine, and from reports from bike shops, this housing should not be used for brakes because it is relatively weak in compression, the principal stress for brake housing. SIS housing is made of 18 strands of 0.5mm diameter round spring steel wire wrapped in a 100mm period helix around a 2.5mm plastic tube. The assembly is held together by a 5mm OD plastic housing to make a relatively stiff cable housing. Because the structural wires lie in a helix, the housing length remains constant when bent in a curve. Each strand of the housing lies both on the inside and outside of the curve so on the average the wire path length remains constant, as does the housing centerline where the control cable resides. Hence, no length change. A brake cable housing, in contrast, changes length with curvature because only the inside of the curve remains at constant length while the outside (and centerline) expands. Shimano recommends this cable only for shift control but makes no special effort to warn against the danger of its use for brakes. It should not be used for anything other than shift cables because SIS housing cannot safely withstand compression. Its wires stand on end and have no compressive strength without the stiff plastic housing that holds them together. They aren't even curved wires, so they splay out when the outer shield is removed. Under continuous high load of braking, the plastic outer housing can burst leaving no support. Besides, in its current design it is only half as flexible as brake cable because its outer shell is made of structurally stiff plastic unlike the brake cable housing that uses a soft vinyl coating. Because brake cables transmit force rather than position, SIS cable, even if safe, would have no benefit. In contrast, with handlebar controls to give precise shift positioning, SIS housing can offer some advantage since the cable must move though steering angles. SIS housing has no benefit for downtube attached shifters because the cable bends do not change.
Subject: 8f.3 STI/Ergo Summary From: Ron Larson <lars@craycos.com> This is the second posting of the summary of STI/Ergo experience. The summary was modified to include more on STI durability and also the range of shifting avaliable from each system. As before, I am open to any comments or inputs. lars THE CASE FOR COMBINED SHIFTERS AND BRAKES. Shifters that are easily accessible from either the brakehoods or the "drop" position are an advantage when sprinting or climbing because the rider is not forced to commit to a single gear or loose power / cadence by sitting down to reach the downtube shifters. They also make it much easier to respond to an unexpected attack. At first the tendency is to shift more than is necessary. This tendency levels out with experience. There is also an early tendency to do most shifting from the bakehoods and the actuators seem to be difficult to reach from the drop position. This discomfort goes away after a few hundred miles of use (hey, how many times have I reached for the downtube on my MTB or thumbshifters on my road bike???). All experienced riders expressed pleasure with the ability to shift while the hands were in any position, at a moments notice. The disadvantages are extra weight, added weight on the handlebars (feels strange at first) and expense. Lack of a friction mode was listed as a disadvantage by a rider who had tried out STI on someone elses bike but does not have Ergo or STI. It was not noted as a problem by riders with extended Ergo / STI experience. A comparison of the weight of Record/Ergo components and the weight of the Record components they would replace reveals that the total weight difference is in the 2 to 4 ounce range (quite a spread - I came up with 2 oz from various catalogs, Colorado Cyclist operator quoted 4 oz of the top of his head). The weight difference for STI seems to be in the same range. The change probably seems to be more because weight is shifted from the downtube to the handlebars. There was some concern from riders who had not used either system regarding the placement of the actuating buttons and levers for Ergo and STI and their affect on hand positions. Riders with experience have not had a problem with the placement of the actuators although one rider stated that the STI brakehoods are more comfortable. ADVANTAGES OF EACH SYSTEM. The Sachs/Ergo system was mentioned as a separate system. In fact (according to publications) it is manufactured By Campagnolo for Sachs and is identical to the Campagnolo system with the exception of spacing of the cogs on the freewheel/cassette. With the Ergo system, all cables can be routed under the handlebar tape while the STI system does not route the derailleur cables under the tape. Those that voiced a preference liked the clean look of the Ergo system. Both Ergo and STI seem to be fairly durable when crashed. Experience of riders who have crashed with either system is that the housings may be scratch and ground down but the system still works. The internal mechanismsof both systems are well protected in a crash. Both Ergo and STI allow a downshift of about 3 cogs at a time. This capability is very handy for shifting to lower gears in a corner to be ready to attack as you come out of the corner or when caught by surprise at a stop light. Ergo also allows a full upshift from the largest to the smallest cog in a single motion while STI requires an upshift of one cog at a time. Riders voiced their satisfaction with both systems. While some would push one system over the other, these opinions were equally split.
Subject: 8f.4 Cassette or Freewheel Hubs From: Jobst Brandt <jobst.brandt@stanfordalumni.org> All cassette hubs are not nearly alike. That is apparent from the outside by their appearance and by the sprockets that fit on them. More important to their longevity is how their insides are designed. Among the mainline brands, some are a response not only to the choice and interchangeability of sprockets but to the problem of broken rear axles and right rear dropouts. These failures are caused by bending loads at the middle of the rear axle that arise from bearing support that is not at the ends of the axle. The following diagrams attempt to categorize the freewheel and hub combination, and two cassette designs with respect to these loads. | H H | | H H Io-- | /-------------------\ -o\ O O------ ===X==================wX========= Axle has weak spot at "w" O O------ (Freewheel & hub) \-------------------/ -o/ H H Io-- | H H | | | | H H | | H H | | | /------------------\ /----\ O O O----O ===X==================XwX====X=== Axle has weak spot at "w" O O O----O (Hugi and Campagnolo) \------------------/ \----/ H H | | | H H | | | | H H | | H H | | | /------------------\/o---o\ O \-----O ===X=========================X=== Axle is loaded only at ends O /-----O (Shimano and SunTour) \------------------/\o---o/ H H | | | H H | | | For clarity only three sprocket gear clusters are shown. Strong cyclists put the greatest load on the axle by the pull of the chain because there is a 2:1 or greater lever ratio from pedal to chainwheel. The freewheel in the first diagram has the greatest overhung load when in the rightmost sprocket. The second design has the greatest bending moment on the axle when in the leftmost sprocket and the third design is independent (in the first order) of chain position. This third design carries its loads on bearings at the ends of the axle for minimum axle stress while the other two put a large bending moment on the middle of the axle. Common freewheel hubs have not only the highest bending stress but the smallest axle at 10mm diameter with threads that help initiate cracking. The second design type generally uses a larger diameter axle to avoid failure. However, these axles still have significant flex that can adversely affect the dropout. There are other important considerations in selecting a hub. Among these are: 1. Durability of the escapement and its angular backlash (t/rev). 2. Flange spacing, offset, and diameter. 3. Type of bearings (cone / cartridge) and environmental immunity. 4. Ease of sprocket replacement and cost. Currently the best solution for sprocket retention is a splined body that allows individual sprockets to be slipped on and be secured by an independent retainer. Screwing sprockets onto the body is indefensible, considering the difficulty of removal. The same goes for freewheels. No longer needing to unscrew tight freewheels is another advantage for cassette hubs.

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