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. 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. As a result, the automatic transmission may not shift correctly and the speedometer readings will not be accurate (as required by law).