I'm changing tire sizes, 14's to 15's. What tooth# would I need to compensate for the taller tire's ?
Not possible to give you an answer, not enough information. You need exact rear tire size, rear gear ratio, and the number of teeth on the DRIVE gear(located on output shaft of transmission)
You don't need to get all that info. Just use your GPS or measured mile & stopwatch or whatever, and measure your speedo error. Then pull the speedo cable out of the trans to see what ratio the teeth on your gears have. Adjust that ratio by the error to see what it should be. Select a new set of gears close to that ratio, oh and check operation. It will more accurate than a calculated gear set (even if you didn't make an error), because it takes into account the exact rolling diameter of your tires. Bruce Roe