Spin Doctor Tech Tip – Maintaining Ceramic Bearings
February 24, 2010 2 Comments
In the search for more speed, the cycling community works on defeating the 3 main forces that try to slow riders down: wind, gravity, and friction. There are wheels, helmets, frames, and forks to beat the wind, components & parts to make bikes lighter, and smoother, more fluid parts to reduce friction.
To reduce friction, the industry has now turned to ceramic bearings. Modern external steel-bearing bottom brackets have tested drag of ~4% of power output. Ceramic bearings generate only ½%, helping to save 4 watts per 100 watts generated.
The friction and heat generated by ceramics is lower for a number of reasons:
- Ceramic bearings are rounder and less compressible (50% harder) than the highest quality steel bearing. This allows parts to be made to tighter tolerances giving a smoother motion with less vibration.
- Ceramics do not conduct electrical current and are chemically inert so they do not oxidize and rust like steel bearings.
- Ceramic balls are less porous than steel so they have less rolling friction.
- Ceramics handle heat better than steel (lower coefficient of thermal expansion). Ceramic bearings will expand and contract 35% less than steel bearings in like conditions. In tight tolerance conditions, added heat can cause bearings to expand and cause binding.
- Ceramic bearings are also 40% lighter than steel bearings creating less rotating mass, allowing for faster acceleration and deceleration.
In our new 2010 Scattante road bike line, ceramic bottom bracket bearings are included with the 2010 Scattante CFR Pro Shimano Dura-Ace Di2 Road Bike and the 2010 Scattante CFR Team Dura-Ace 7900 Road Bike.
But one common complaint about ceramic bearings is that when used with steel races (hybrid ceramic bearing) they are so hard that they cause premature scoring and pitting of the steel tracks. At the core of this issue is a lack of maintenance. This is considered a pro level component and requires pro level maintenance. Just like race cars that are rebuilt after every race, ceramic bearings are not an install and forget about it component.
Hybrid ceramic bearings need regular maintenance and that begins with silicone grease. Silicone grease handles temperature better than other grease and it will not degrade rubber seals. FSA recommends inspecting the bearings:
- After each riding season or after 8,000-10,000 KM, whichever comes first
- After use in rain, mud or wet conditions
- After drive train has been cleaned with solvents or sprayed by high pressure water jets
- Anytime rotational smoothness, evidence of corrosion, or seal damage is apparent
Most manufacturers warn that ceramic bearings can NOT be acceptably maintained unless the cartridges are removed from the bike component, e.g. hub shell, BB cup, etc.
Here are the steps that FSA recommends to remove the bearings:
- Remove bearing cup from bike.
- Use a bearing press to remove bearing cartridge from cup (HS, BB, Hub). Enduro Fork Seal makes a good tool for removal/installation of bearings from external BB cups, http://www.enduroforkseals.com/id114.html.
- Use an Exacto® knife or preferably a seal pick to remove seal. Be careful not to damage or bend the round metal stiffener in the seal.
- If possible, carefully remove plastic ball retaining cage from cartridge. The balls will remain in the cartridge. For some bearings this may not be possible. If you are concerned about damaging the retainer, cleaning and relubing can be accomplished w/o removing it.
- If you have removed the retainer cage, slide bearings to one side and pull inside race out toward you as you clean around the bearing.
- Clean dirt and old grease from bearing. Use a gentle solvent. Do NOT use alkali or acid based solvents.
- Let bearing dry completely.
- Grease bearing using silicone grease. FSA recommends using a grease syringe. [If you use a syringe, use it only w silicone grease- don’t mix grease types.]
- Rotate bearing to better distribute grease.
- Carefully reinstall seal(s).
- Reinstall bearing in cup.
But remember, if you’re not ready to try this on your own. . .
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