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.

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