Hypertech's Speedometer Calibrator can correct the speedometer for tires up to 54 inches (depending on the application). Simply plug in the Speedometer Calibrator into the vehicle's diagnostic port under the dash, select the tire height and/or new rear gear ratio that has been installed, and the vehicle's computer is reprogrammed for accurate speedometer readings (as required by law). The Speedometer Calibrator also reads/displays/clears DTCs and is internet updateable. The Speedometer Calibrator is emissions certified 50-state legal (application specific).