>If you attempt to do these calculations by reference to
>circumference you will introduce unavoidable errors into your
>calculations because circumference bears only a loose correlation to
>revolutions per mile conditions for any given tire. Revolutions per
>mile is the only thing that matters as far as your gears are
>concerned. For accuracy, it is best to use manufacturers' stated
>revolutions per mile at X MPH for each tire and IGNORE both tire
>height and IGNORE tire circumference information. A revolutions per
>mile number that matches what one would get by calculating that
>number based on either tire height or circumference is almost
>certainly not accurate.

All dependent on tire inflation pressure and vehicle mass. Lower
pressure means greater indentation (smaller radius) at contact patch,
therefore higher RPM.
--
Andrew Grebneff
165 Evans St, Dunedin 9001, New Zealand
<andrew.grebneff@stonebow.otago.ac.nz>
Seashell, Macintosh, VW/Toyota van nut