Good question. I assume you mean steel rings and ceramic balls as opposed to full ceramic bearings. Ceramic bearings are marketed as better due to lower friction between balls and raceways (the grooves on the inner and outer rings that the balls run in) and longer life. The balls are lighter and harder and generate less friction when in contact with steel than steel to steel contact. What does this mean for the cyclist? Well, it does mean longer life. Ceramic bearings will usually last a lot longer but then they cost a lot more so are there benefits elsewhere?

The effort required to rotate a bearing depends on various things (http://www.smbbearings.com/SMBtechda...ictionaltorque). Most ceramic bearings on the market are made in China with tolerances that are not as good as a good quality Japanese or Western made bearing. The inferior roundness means they will not turn as easily. If they happened to have a poor choice of lubricant (e.g. a high viscosity grease) and the wrong seal type, you could have a much less free-turning bearing than some of the cheap bearings with steel balls.

If you want a bearing to last longer, get the ceramic ones. If you want superior performance, that is more difficult and you would probably need a bearing torque tester to be sure. I would say that a high precision all-steel bearing with correct lubrication and seal type would give less rolling resistance than most of the ceramic bearings out there. We are looking at ceramic bearings but we intend to get some comparative testing done against the precison all-steel type before we decide. Of course to buy an expensive bearing is only really worth it if you perform at a high level on road or track where fractions of seconds make a big difference. If not, save your money and get a standard one.

I hope that helps.