re:  "All dependent on tire inflation pressure and vehicle mass. Lower
pressure means greater indentation (smaller radius) at contact patch,
therefore higher RPM."

Ok.  I need some help understanding this.  Isn't the radial tire tread
similar to a tank track in that its length doesn't change no matter how
heavily loaded?  (If it matters, assume steel belted.)  And that tread
must still travel its full length in exactly one revolution.  So what
difference does the variable radius have on RPM?  What am I missing?

//Jack

On 6 Oct 2002, at 12:08, Andrew Grebneff wrote:

> >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