Brent, et all, the static radius measurement of finding the tire revs
per mile is complete bunk. Tire pressure, even fairly extreme
variations, make almost no difference in the actual revs per mile but it
makes a huge difference in the measured static height and the subsequent
calculated revs per mile. At least at low speeds there is no meaningful
difference. I just did the "mustard" test on both left side wheels, and
then let most of the air out of one tire and did the mustard test again.
The facts speak for themselves. I will post them soon.

Mark

brent@vanagon.com wrote:
>
> I have been sitting on the sidelines on this one, but I suddenly felt compelled to add my 2 cents' worth...
>
> One of the things I have not heard anyone discuss is the difference in diameter of a tire while standing vs. while traveling at 70 mph.  Surely there must be a difference.  Also, if you think about the physics of it, a tire is not actually *round* while it it turning on a vehicle, is it?  It has a flat spot where it contacts the road.  This distortion could certainly introduce errors into a formula based upon the "static" diameter of a tire (i.e. measured while mounted on the car, or simply mounted on a wheel laying on the ground)
>
> Kinda make you go "Hmmmmmm....?"
>
> Brent Christensen