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Bicycle Bottom Brackets with Ceramic Bearings
Good, Bad or Just Expensive?

Life would be so easy if we all had an unlimited bank account or a corporate sponsor to buy all the newest in bicycle part technology, but reality sets in and choices must be made. What I want to know is if the hype about ceramic ball bearings used in bottom brackets, hubs and headsets is really worth looking into or is this just another over priced gadget that is great to talk about over a beer?

Ceramics are relatively new to the bicycle industry. With the exception of a few companies like FSA, cranksets and other bike parts have typically used "steel" bearing. But ceramics have been around in the industrial arena for a number of years for cutting tools, turbines and even in satellites.

Companies like SKF spends millions of dollars on bearing research and have even sponsored the Ferrrari racing team since 1947 to give themselves a platform to test their new technologies. Did you know that today's Ferrari F1 racers contain over 150 SKF bearings and seals? And you better believe that if just one-half horspower can be gained through reduced bearing friction, then racers will be having serious discussion about bearing technology. Anyways I'm getting a little sidetracked but here's a list of why a serious racer might want to consider ceramic bearings like those used in some of the FSA cranksets.

So what's the big deal?

35% less Thermal Expansion:
Think of putting a coke in the freezer. You have to allow for its expansion or you'll blow the tin. Steel bearings are like the tin of pop. Ceramics on the other hand change size significantly less then steel with a given shift in temperature, thus raceways, rings and seals from a typical bearing can be made to much greater tolerances. They can even be fabricated with a smoother finish so vibration goes down and stability goes up.

50% less Conductivity:
Ceramics are electrically NON-conductive, and chemically inert, thus do not suffer from oxidation and the rust that degrades the surface of a traditional steel ball bearing. They suffer less heat damage since they don't heat up as easily. This helps to maintain the spherical geometry of the ball bearings and significantly reduces your repair time.

60% less Weight:
Since silicon nitride is only about 40% of the weight of bearing steel the savings are obvious. Think about tying a heavy rock to the end of a rope. Its hard to get in motion and hard to stop. The lighter the rock the easier it is.

The issue of bearing weight is the same story. The heavier they are the more effort it takes to get them rolling and stopping. Thus ceramic bearings, with less then half the weight, and thus less rotating mass, will be much more responsive in acceleration and deceleration, with much less effort.

50% Higher Modulus of Elasticity:
that's just a fancy way to test how easy it is to deform something. Ceramic has a 50% higher modulus of elasticity, so it takes a lot of work to alter its original shape. That gives you a much longer life expectancy in a hard wear zone like a bicycle's bottom bracket.

Cold Welding:
Steel on steel has a nasty habit of welding itself together, that's why you use anti-seize on some fittings. In a bearing the lubricate helps to prevent this but when bearings sit over the winter this can happen. Ceramic is NOT able to weld itself to steel. Steel and Ceramic are incompatible in that respect so cold welding is another difficulty you can avoid with ceramic ball bearings.

So what does this mean to a company like FSA that has chosen to make some of its bike parts with ceramic bearing? Studies by a number of cycling magazines, FSA and even bearing companies like SKF have repeatedly shown extended life expectancy.

Research suggests that FSA Bottom brackets equipped with ceramic bearings have a 5-10 times longer life. Industrial literature might suggest ceramics add 3-5 times the life expectancy. Either way we know they'll be there longer than their carbon steel cousin.

Equally exciting, in tests with Olympic and professional racers and in controlled lab tests with wheels, ceramic bearings repeatedly show significantly less friction, making for faster speeds, acceleration and deceleration with less force.

So whats not to like? Only the price. Ceramic Bearings are easy to justify with longer life, less vibration, more speed but at maybe 5 times the price of traditional bearings the questions still remains as to whether you can justify the added cost?

Approximate values: Silicon Nitride Zirconium Oxide Steel
Density .11 lb/in3 .21 lb/in3 .28 lb/in3

Hardness (Vickers Hardness Scale)
1580 kg/mm2 1300 kg/mm2 700 kg/mm2
Maximum Use Temperature 1000C 1500 C 300F
Corrosion Resistance Excellent
-Chemically inert
  Poor

 

Related Articles:
Bicycle Cranksets Components: Bottom brackets, cranks & chainrings

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copyright Jan. 2007