You need to know your drive tires rotations per mile, most tire manufacturers list tires specs online, search for your model/size tire. Multiply rotations per mile by the axle ratio, then multiply that by 16 (16 teeth on the VSS ring). That will give you total pulses per mile. Once you know the pulses per mile, you need a computer with Caterpillar ET, you adjust pulses per mile in the VSS parameters.