Why not full ceramic?
A question we get from customers is: Why don't you offer full ceramic bearings?
First, let's explain what a full ceramic bearing is and what a hybrid ceramic bearing is. Both use ceramic balls, so they are the same there. The difference is that hybrid ceramic bearings use a special hardened metal race (hardened to withstand the hardness of the ceramic ball) while a full ceramic bearing uses a ceramic race.
Ceramic races make for a slightly lighter bearing and can be used with little to no grease. Plus they can't rust, usually don't pit nor suffer from wear. Sounds great, right? Yes! But there is a huge catch, keep reading.
It makes sense to think that a full ceramic bearing would be better, I mean, if ceramic balls are so good, why not use a ceramic race too? A lighter, faster bearing that uses less grease is a dream bearing. But, in practice it can be a nightmare.
There are several reasons, one is the high cost, but most cyclists will pay for better performance, so cost isn't the issue. So what is the real reason that full ceramic is not good? Simple, they aren't designed for use in cycling where loads and impacts vary greatly over the course of the bearing's lifespan. Or to put it simpler, ceramic is a great, strong material for the ball, but for the race, which absorbs shocks and impacts, it is too brittle. This means that when you hit that pothole (although you should try to avoid them!) or those train tracks, the races can crack. Any type of impact or sudden load can crack a ceramic race. Did you bunny hop that obstacle in the road? Uh-Oh! Better check those ceramic races.
The companies pushing full ceramic bearings are the companies that get their bearings from large industrial bearing makers. Why is this important? Industrial bearings are designed to work in machines and controlled environments. Cycling bearings are not. So a full ceramic bearing is great for a machine that never has to withstand any impact, but not good for cycling. There are numerous reports on the interwebs about cracked full ceramic bearings in wheels and BBs. The customer likes to blame to bearing brand, and they should, but not because the bearings cracked but rather because the company sold them in the first place.
About the only safe place to use full ceramic bearings on a bicycle is the pulleys. These are not subject to impact loads like wheels and bottom brackets are. We've been testing full ceramic pulleys for a year and may release them at some point... stay tuned!