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.

I leave it as an exercise for the interested to evaluate the change in the Q
per change in rotor diameter.


"Michael" wrote in message
om...
I just noticed that Avid's mechanical disc brakes come with 160, 185
or 203 mm rotors. It's claimed that the 185mm rotor has 15% more
"power", the 203 26% more.

Does a larger rotor really provide more stopping power? Why? I could
understand less fade due to heat, since a larger rotor would dissipate
heat better. Does that translate into more "power"?

I assume that dimension is the rotor diameter. But wouldn't a change
in rotor diameter change where the caliper gets positioned, i.e. would
require a change to the caliper mounting eyelets?

I'm spec'ing these brakes for a road bike; should I expect to need
more stopping power than a mountain bike for say long mountain
downhills?

TIA