SM>Can someone please explain just what a "gear inch" is and how to measure
SM>it?  I know it has something to do with how far the tire moves for a given
SM>pedal input but I'm not clear on the details.
"Gear-inches" is a term used to describe how far one will travel for one
revolution of the crank. The term comes from the time of the
"high-wheeler" when the pedals were attached directly to the front
wheel. "Gear-inches" would be the apparent diametre of the wheel - thus
a gear ratio of 60 gear-inches would give the same foward distance per
pedal revolution as with a 60" diametre wheel. To find the gear-inches
of your various gear ratios, you divide the number of teeth of the chain
ring by the number of teeth of the rear cog, and multiply this by the
diametre of the rear wheel.
An equivalent system is call "development" in which the true
circumference of the rear wheel ( outer edge of tire ) is multiplied by
the result of dividing the tooth number of the chain ring by the tooth
number of the rear cog. This give the actual forward distance per
revolution of the crank.
Sound compicated? See John Forester's Effective cycling for a very lucid
explaination.
 * SLMR 2.1a * Phil, the cyclist from Scarborough...
--- Maximus/2 3.00
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