Sry for yet another gear thread but when i did a search i got too many hits. Anyway, i just fixed my speedo and its off by 10-15mph so im wondering if one of the previous owners mightve swapped gears. What the calculation where you can rotate the driveshaft (or was it the tire?) and count the number of rotations it takes to turn the tire? Also, does a bigger then stock tire have any effect on this calculation?