Tech on a Postcard - Ceramic Bearings

May 13, 2008
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Kawasaki-Shi
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What are they?
Ceramic races that hold ceramics balls to form a bearing. More common, cheaper and practical are the hybrid ceramic bearings utilising ferrous races. The ceramics used are usually silicon nitride or zirconium dioxide.

Where are they used?
Hybrid ceramic bearings were originally and still are used in machine tool spindles (e.g. CNC) which require high rpm, stiffness and reduced lubrication systems. They are also used in turbomolecular pumps, high speed dental tools and turbo chargers. Full ceramic bearings are used where electrical isolation is required. Recreational uses include bicycles, fishing reels and various skating categories.

What are the main advantages compared to steel bearings?
  • Lower coefficient of friction and lower operating temperatures
  • Lubricant free applications (semiconductor industry, full ceramic species are also used)
  • Bearings are stiffer (more accurate positioning of spindles)
  • Ceramic is less dense
  • Higher rotational speeds (some turbomelucular pumps have a standby mode of 60 000 rpm and are operational at 90 000 rpm, some bearings need to accelerate to 40 000 rpm in 100 ms)
  • High temperature usage (lower coefficient of expansion, material dependent over 1 000 deg C)
  • Highly corrosion resistant (full ceramic species used in pumps for corrosive fluids)
  • Long life (2 to 100 times experienced in industry)
  • Allows equipment to operate at its optimal speed constantly

The next development in speed has already arrived in the form of magnetic bearings (MAGLEV) that have no known rotational speed limits.

Standards
ABMA/ANSI/ISO
ABEC – the higher the number the more precise and accurate the ceramic ball i.e. tighter tolerances

What it means for cycling
Bearings are found in the headset, hubs, bottom bracket and jockey wheels. Since the bearings of the hubs work the hardest amongst them, this would be the first set to upgrade, if at all. Assume we can ride at a constant 40 km/h, that means our 700 x 23c wheel/tyre will rotate at 322 rpm and even with ceramic hybrid bearings we won't notice the reduction in friction whilst trying to overcome air resistance. Where you might notice the difference is in freewheeling, accelerating and maybe 2 or 3 extra km/h downhill. Even pedalling our wheels to a minimum constant of 3 000 rpm which is... 377 km/h, we are only likely to save 0.2 W at the bearings (at 3000 rpm full ceramic vs hybrid, the saving is 1.2 W). In terms of energy saving, 20% to 30% friction is reduced at the rolling contact which can be easily negated by overpacking the bearings with grease (those few precious grams saved will also be reduced) slowing you down.

Worth the upgrade?
In a word... No. If you've got some spare change or nothing left to upgrade or need a brag or a placebo or wonder if this is really true then why not? At the very least you’ll save a few grams (extreme weight weenie) and perhaps one or two watts on a veeeeery long ride.

Much cheaper and less exotic, but regular maintenance, keeping your bicycle clean, lubricated, appropriate choice of tyres pumped to their optimum pressure and a few beers less a week, you're more likely to experience a higher performance gain than fitting a full set of hybrid ceramic bearings.

http://www.analyticcycling.com/ForcesTires_Page.html

The first person to fit all the above, including title and URL, onto one side of a standard size Japanese postcard in their own handwriting wins a beer. Should there be a draw you'll have to share the chujokki.