The vehicle's computer calculates your vehicle's speed based on the diameter of the stock tires.
If you've installed taller or shorter tires, or changed the rear gear ratio, the vehicle's computer doesn't know how fast your vehicle is going. Corrects speedometer readings after installing non-stock tire sizes or changing rear gear ratios;Correct speedometer for accurate readings (as required by law) for tire sizes up to 54;Large 4.If you've installed tires that are larger or smaller than original equipment tires, or if you have installed a ring and pinion gear set with a different rear gear ratio, the Max Energy Spectrum allows you to re-program for correct speedometer readings, as well as correct part-throttle shifting..