Fred I can see you have not GOT IT yet. Ok when one tire is severly deflated...as in SAND.. The PATCH on the ground gets wider and LONGER so it is in contact with the sand more than a fully inflated tire of the same size. Yes the bottom radius is changed (shorter) But the circumference has NOT changed! It takes the same amount of INCHES for both tires to turn one complete turn..
With your theory one could run his tires low and the speedometer would be INCORRECT!
Remember i is all about the circumference not the radius.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />