Originally Posted by Duragrouch

The bearing balls rotate. At the outer periphery, i.e., the outer race or cup, they roll with a surface movement at a given rate. Now transfer that same ball rotation rate to the bearing inner periphery, i.e., the inner race or spindle; You will have the same surface rate, no slipping, however because the inner race is smaller diameter, it will have a *higher rotational speed*, revolutions, than the speed differential at the outer race. If, for example, the inner race contact diameter is 1/2 the outer race contact diameter, the inner race rotational speed with be 2X the speed differential compared to between the balls and the outer race.