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Old July 12th 03, 05:06 AM
Chris B.
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Default Disc brake rotor size

On Fri, 11 Jul 2003 19:35:18 GMT, Jose Rizal wrote:

Doug Huffman:

The power of a brake is its convective heat transfer rate and proportional
to Q = UA(Th - Tc) where Q is the heat transfer rate, U the convective heat
transfer coefficient, A the area and a function of rotor diameter, Th the
temperature of the rotor and Tc the cooling air.

Incorrect. This is only an indication of the heat generated by the
brake, not its stopping power.

Maybe this is the bigger issue though. Since the OP wants to use disc
brakes for "long mountain downhills" isn't heat going to be his
biggest problem? I just took a few measurements and did a few
calculations and found that even a 205mm disc rotor has only about 50%
of the swept area of even a 26" MTB rim. I wonder whether a person
would be more likely to have a tire blow off while using a rim brake
or having the rotor warp.

The only real advantage I see to using the disc brake is that it's
performance won't decline as much in the wet. Hardly worth all the
disadvantages IMO, especially on a road bike.

Chris Bird

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