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Author: hammerpe
Time: 07/04/03 00:07 PST
This is a reply to message no. 11530 by caroline7c
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Current Topic:
aluminum vs. steel in brake disc
I have done a lot of work on designing brake rotors for mountain bikes, but am very familiar with auto and motorcyle applications as well.   I found that the an aluminum/ceramic composite (metal matrix) makes an excellent lightweight rotor. It has very good wear characteristics and has good strength. Desigining the rotor correctly for thermal expansion is key as the material is brittle and thermal fatigue can be an issue. At the time I was doing research (5+ years ago) Karts were using MMC rotors and they held up pretty well.
Regular aluminum simply cannot hold up to wear. Even with ceramic coating or anodizing thermal cycles really wreak havoc on the whole system causing the coatings to crack microscopically and eventually wear through. They will work for a little while but will wear out quickly. Organic pad compunds can help reduce wear by keeping the heat down, and tend to be softer than sintered pads.
As far as analyzing this how detailed do you want to get?  An easy way to do simple testing (depending on the strength of the brake/lathe system) with just some thermocouples/pressure guages/heat gun is to use a lathe. You just have to fabricate a fixture to hold the caliper properly. You can mount the test rotors on the lathe spin them up and apply the brake.  You can get some fairly good data, enough to point you in the right direction.

Hope this helps

-Paul
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