All ceramic bearings are not created equal. Just as there are various ABEC grades of steel bearings that rate smoothness and rolling resistance, a similar rating system applies to ceramic bearings. There are two types ceramic bearings—hybrid ceramic bearings and full ceramic bearings. Within those categories there are gradations based on smoothness of both the balls and the races, and in the uniformity of size.
Hybrid ceramic bearings have steel races and ceramic balls. They are a bit lighter than steel bearings only because of the weight difference in the balls alone. They roll a bit faster than even the best steel bearings because the balls are smoother, harder, rounder, and more uniform in size, and the steel races are often ground smoother as well.
The friction in a typical bearing with silicon nitride balls and steel rings is about 10 percent less than in an all-steel bearing of the highest quality.