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Steel -cheap, most common -very good durability -easy to weld(cheap production cost) -flexier. The ride is more forgiving, but wastes more energy. I usually recommend someone who is below 180 to ride a steel frame -unless the frame is very expensive, it's usually heavier than aluminum -will rust Aluminum -slightly more expensive than steel, but coming down in price -some people question durability, however, frames have lifetime warrenties, so you shouldn't let this hold you back -slightly harder to weld/bond, but can be done -very stiff. The ride is rigid, power can be delivered more directly, however, the ride is harsher -usually lighter than similarly equipped steel bike -come in all sorts of cool colors and won't rust when exposed to the environment(Note, aluminum will oxidized, but this is differen't than rust) Titanium -one of the most expensive frames, good stuff -durability is very good, assuming you find the right builder -it's very hard to bond, if the builder is experienced, the frame will be great. If not, you might be in trouble -some frames can be made to have the horizontal stiffness of aluminum but with the vertical flex of steel frames, making this one of the more desirable material. However, if not done properly, the frame can feel dead, much like any other frames -usually about the same weight as the aluminum frames, sometimes a bit more, sometimes a bit less Carbon Fibre -very expensive also -durability is ok. The fibres can unwoven/break microscopicly by each bump. At the end, the unwoven spot will fail by breaking. -it's usually molded -some people find these frames flexy. However, some manufactuer will use carbon main frame only with al lugs and rear triangle. CF tends to be flexy at times, however, like any other material, it can be made to be very good. -usually very light. I'm sure a lot more people will add stuff/correct me. Please do! John Stevenson [email@example.com] Preamble: there are no bad materials, only bad applications. Almost any material you can think of can be built into successful mountain bike frames, providing the engineer who does the design work knows the strengths and weaknesses of the material, how to use and compensate for them, and, most importantly, how to translate those concepts into production processes that build reliable bike frames. All materials are available in different grades, with stronger grades usually being more expensive. Plain carbon steel, as used for department store junkers, has an ultimate tensile strength of about half that of the heat-treated alloy steels used in very high-end steel frames.Stronger steels make for more expensive frames because, while the raw material is relatively cheap, its very strength means that shaping it into tubes, cutting and joining those tubes is more time consuming and hence costly. Price ranges Rather than saying a material is/is not cheap, why not do it like this: Bike cost ($US): 0 500 1000 2000 4000 8000 | | | | | | Frame materials: <------steel------> <---aluminium------------> <--------titanium----> <----carbon fibre------> and so on. You might like to get the right US price bands, as I don't have easy access to that info >Steel >-cheap, most common >-very good durability >-easy to weld (cheap production cost) >-flexier. The ride is more forgiving, but wastes more energy. I usually >recommend someone who is below 180 to ride a steel frame Bzzzt! 'wastes more energy' definitely unproven, probably unprovable, probably untrue. There have been some very long, tedious and circular discussions of the whole issue of the actual effect of frame flex on efficiency in r.b.tech. Given the calibre of the minds there that have failed to reach meaningful conclusions, I think it's safer for you and me to leave this one alone rather than repeat folk misconceptions. I will say that it's very hard to imagine that, say, Henrik Djernis could have ridden steel frames to three world championships if they wasted any significant amount of energy. The fact that world titles and world cup races have been won on virtually every frame material under the sun implies that the differences between materials as far as energy transfer efficiency goes are negligible at best and nonexistant at worst. >-unless the frame is very expensive, it's usually heavier than aluminum Have you actually weighed a low-end aluminium frame recently. Some of them are getting very heavy >-will rust > Unless looked after. >Aluminum >-slightly more expensive than steel, but coming down in price >-some people question durability, however, frames have lifetime >warrenties, so you shouldn't let this hold you back A broken aluminium frame waiting for a free replacement is still a bike you can't ride. Bit of a bummer in June. >-slightly harder to weld/bond, but can be done Actually, quite easy to bond, which is why it's often done in preference to welding. >-very stiff. The ride is rigid, power can be delivered more directly, >however, the ride is harsher It should be said here that this is a property of the application not the material. Aluminium is more flexible than steel and has the annoying property of lacking a definite cyclic stress fatigue limit. This means that however small the repeated stress it is subjected to, an aluminium part will eventually fail because of metal fatigue. A steel part, on the other hand hand, has a cyclic stress level, below which it will last forever. To get round this, designers build aluminium frames so their cyclic stress levels are as low as possible to maximise their lifespan. In practice this means using large-diameter, thin walled tubes, which also happen to be light and rigid. In theory you could also build very light steel frames by using thin-walled, large diameter tubes, since the fatigue limit stress of good steel is usually higher than that of the aluminium alloys typically used in bikes. However, thin-walled steel is hard to weld and tends to be rather easy to crush. Aluminium's lower density means it's tubes are thicker-walled and less prone to crushing. >-usually lighter than similarly equipped steel bike >-come in all sorts of cool colors and won't rust when exposed to the >environment (Note, aluminum will oxidized, but this is differen't than >rust) In certain environments, particularly salty ones, aluminium is prone to corrosion. Certain aluminium alloys must be painted or they will corrode on contact with air. > >Titanium >-one of the most expensive frames, good stuff Actually the quality now varies almost as widely as steel and aluminium. There are some quite inexpensive titanium frames on the market, but they tend to use lower grades of material than the 3 percent aluminium, 2.5 per cent vanadium alloy that's used by quality builders such as Merlin and Litespeed. >-durability is very good, assuming you find the right builder >-it's very hard to bond, if the builder is experienced, the frame will be >great. If not, you might be in trouble Gary Helfrich will be along in a moment to claim that this is bollocks and that titanium is only slightly harder to weld than steel and much easier than aluminium. Also you're confusing welding with bonding, two totally different processes. >-some frames can be made to have the horizontal stiffness of aluminum but >with the vertical flex of steel frames, making this one of the more >desirable material. Sorry, but this is just plain bollocks. Bike frames are damn nearly perfectly rigid in the vertical plane, whatever they are built from. There's no doubt that there are material/configuration factors that affect how a frame feels, but these are probably to do with the way the frame dissipates or transmits vibration, rather than the Young's modulus of the material. However, if not done properly, the frame can feel >dead, much like any other frames I've never understood what people mean by a 'dead' frame. I suspect it's another piece of bike culture folk bollocks. >-usually about the same weight as the aluminum frames, sometimes a bit >more, sometimes a bit less > >Carbon Fibre >-very expensive also Priced a Giant carbon fibre bike recently? >-durability is ok. The fibres can unwoven/break microscopicly by each >bump. At the end, the unwoven spot will fail by breaking >-it's usually molded Er, half. Carbon tubes are usually molded, but are then joined into frames by bonding into lugs. Trek, Giant use this process and they must account of the majority of carbon frames out there. >-some people find these frames flexy. Some people can convince themselves of anything in order to pander to their prejudices. Which isn't to say that carbon frames aren't flexible, no doubt some are, but this is just more repetition of 'lots of people say this so it must be true' bike folklore bollocks.