Tire radiuses have to be matched so that the ratio of the
front and rear axle speeds produces the correct ground
speeds. Because the front wheels are smaller, they have to
roll more quickly than the rear wheels to give approximately the same ground speed for both tires. This speed
difference is even higher because of the fact that the front
wheels usually turn slightly faster compared to the speed
value that would give exactly the same ground speed as
the rear tires. The transmission has a front axle lead ratio
(zp), defined by