Measured "running" tire circumference VS Manufacturer's numbers
I have a dilemma that I can't seem to get my head around. . .
In calculating gearing options for a modified vehicle, I am using the measured distance from the ground to the center of the axle of a pneumatic drive tire.
I figure that is the lever arm and is the ONLY number that should be used to determine my distance traveled.
(Radius (distance from ground to axle center) X 2) X pi)) = "running" circumference.
However, several folks keep telling me that I [U]must[/U] use the tire manufacturer's calculation for that size tire (which is not the same as the one I have measured).
While the differences are slight, they do change the final ratio, and I'd like to know if I am misunderstanding things, or am correct in my calculations.