Went from the OEM 215/75R15 to a 235/70R16. From researching the speedometer accuracy question, concluded I would need to change the gear by one tooth. Read here that the speedometer can be verified with a GPS unit which I never thought of. So I checked it & much to my surprise, it was accurate! Tires are at 40% of tread life, which when replaced, might affect the accuracy but imo not enough to warrant replacing the speedometer gear.
Speedometer calibration
