Hypertech's Speedometer Calibrator can correct the speedometer for tires up to 54 inches (depending on the application), and/or non-stock rear gear ratios. Simply plug Hypertech's Speedometer Calibrator into the vehicle's under-dash connector, select the new tire height and/or new rear gear ratio, and in a matter of minutes, the vehicle's computer is reprogrammed for accurate readings (as required by law).