Originally Posted by
FL_Gator
I think the proposed explanation is that the deformation of the tire under weight is consistent for the entire revolution, thus the reduced radius is consistent for the entire revolution and therefore the effective circumference loaded is less than an unloaded circumference.
To my mind it's kinda like calculating ERD when building wheels. Hard to measure directly w/o some sophisticated tools but the concept is fundamental to getting spoke length right.
With tires on wheels, when tires aren't loaded the
effective circumference is
greater (corrected thanks to Choddo for calling me out on my error) than when the tire is loaded. It's not the distance traveled so much as the lever arm of the wheel's
effective radius when loaded that affects calculations when that variable's plugged in.