Date:         Sun, 6 Oct 2002 12:08:14 +1300
Reply-To:     Andrew Grebneff <andrew.grebneff@STONEBOW.OTAGO.AC.NZ>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Andrew Grebneff <andrew.grebneff@STONEBOW.OTAGO.AC.NZ>
Subject:      Re: Tire size vs. Engine RPM
In-Reply-To:  <4.3.2.7.2.20021005133236.0537ea10@pop.rcn.com>
Content-type: text/plain; format=flowed; charset=us-ascii

>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