Are ceramic bearings better than steel bearings? We get this one, or a question like it, daily. The quick answer is, “Yes, they are, as long as they are properly engineered and manufactured like ours are”, but one of the big reasons why ceramics are better is not what most people expect. It’s important for you the reader the know that the reasons why we say “Yes” are practical and not the reasons given by those who hawk ceramics by showing you things like a sledge hammer striking a ceramic ball and the ball coming away unscathed, or some such nonsense. As you read this you’ll find out why this and other “tests” like it are, at best, misleading.
At this juncture, it’s vitally important that we get specific regarding this conversation on two key points. Firstly, when we say “ceramics” we mean hybrid ceramic bearings, which are made up of ceramic balls running in steel races. Secondly, we are only addressing human powered equipment which operates at relatively low-wattage inputs, at low operating temperatures, and at a measly 80-110 RPMs. I realize there are massive studs among us that can churn out 1,700 W at 120 RPMs for several seconds, but when we consider that the dynamic load rating for an off the shelf BB30 bearing (6806) is over 4,500 W at 10,000 RPMs---and this work lasts minutes rather than seconds---we see that humans put very little strain on a properly engineered bearing.
But before we get to why hybrid ceramic bearings are better than steel for a bicycle bottom bracket, let’s go over some common misconceptions about ceramic bearings.
Crappy ones don’t, that’s for sure. And it’s not ultimately the fault of the balls because making super round ceramic balls that are harder than steel is not as difficult as is manufacturing super round steel balls. This super-hardness of the balls is exactly why most hybrid ceramic bearings don’t last, simply because the balls pound the steel races into oblivion, often rapidly. Most companies that make hybrid ceramics just use the same races for everything. Steel bearings, ceramic bearings, it just doesn’t matter. But it does matter. Specific metallurgy, balanced internal tolerances, and the all-important finish polishing of the race-channels the balls run in are crucial factors in the creation of a proper hybrid ceramic bearing that will last, such as our Ceramitech line of bike bearings. These considerations and processes are not as critical on steel bearings and are the primary reason why ceramics are more expensive. So, in the final analysis on durability, or lack thereof, everything really boils down to the races, which is why the blurb accompanying our Ceramitech bearings is all about the races. And this is also why showing a hammer smacking a ceramic ball doesn’t prove anything significant.
This one is fairly silly, and we’re surprised to hear these words as often as we do. As already mentioned, just about any other application of bearings will be more demanding than in human powered equipment if we remove purely environmental factors like dirt and grim and water contamination. Someone usually cites the use of ceramics in turbochargers as proof of their high RPM/ high heat claim, but this isn’t a reason, it’s a statement. True; ceramics are used in turbos, which see upwards of 100,000 RPMs in a street car, day after day, and operate at insane temperatures, but I’ve always thought that referring to such an impressive application of hybrid ceramics as a funny way to dissuade me from desiring them. That’s like saying, “Man, you don’t want a woman that incredibly beautiful because other men will be looking at her all the time and you might get jealous a lot”. Stating how fantastic hybrid ceramic bearings are in turbos makes anyone listening think, “Gee, if it can handle all that torture then think of how good that’ll be in my bike”, and so it goes. And this leads us to the reason why ceramics are better in a bicycle bottom bracket application than are steel bearings, and that is the absence of high heat and high RPMs in your bottom bracket.
Virtually all drag in any sealed bearing is cause by the grease. Steel bearings require more grease that is of a substantially higher viscosity than do hybrid ceramic bearings if they are to survive very long because steel on steel is, of course, no bueno. This grease-drag isn’t a problem when a BB30 (6806) bearing is in an electric motor that goes from 0-7,000 RPMs in less than a second. At this speed the grease will heat up and partially liquify in just a few seconds, slashing the grease-drag by upwards of 80%. We spin bearings up on our bench tester and I can tell you that after just 30 seconds of spin at 7,000rpms the bearing gets too hot to hold with bare hands. A ½ hp electric motor doesn’t care if its bearing grease is thick, but you should. Consider that you’ll never get that bearing hot enough to liquify that grease just by pedaling your bike, and so with steel bearings you’re just churning peanut butter stroke after stroke.
Our Ceramitech hybrid bearings feature the roundest balls running in properly engineered, micro-polished races AND they require substantially less grease compared to steel bearings to maintain comparable durability. Our hybrid ceramic bearings get a 30% grease fill of an ultra-low viscosity grease that would be completely unsuitable for steel bearings. The viscosity is so low in fact that if liquification did occur it’d all run out. But don’t worry, that won’t happen because you can’t generate that much frictional heat from pedaling on a functioning system nor could you tolerate riding in a temperature high enough to cause the grease to melt.
The Bottom Line: Quality hybrid ceramic bearings are better than steel bearings in a bicycle bottom bracket application because they have rounder balls for lower resistance, better races for lower resistance, and are grease-efficient in low RPM, low heat environments for lower resistance.
I just know some smart aleck is thinking he’s just going to put a small amount of light grease in regular steel bearings to cheat The System, The Man, what have you. You can do this, and it will increase efficiency. Racers sometimes run just a smear of grease or light oil in bearings just for a crit or a TT to eke out every last watt. But for a daily rider this is impractical and will lead to extremely low lifespans for your equipment. If you want the sizable, measurable advantage of hybrid ceramic bearings, just buy the ceramic bearings. And if you want ones that last, buy Ceramitechs.
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