Originally Posted by
Dean V
A disc brake can out perform a drum brake. This has been shown for their use in anything performance orientated for over 50 years. However bicycle discs are typically so thin and light they simply can't cope with dissipating much energy. A drum brake like an Arai, whilst being technically not as efficient as a disc, there is so much more of it that it that it can cope with dissipating more heat. If you were to put a good disc brake system on your tandem that weighed as much as an Arai drum brake I am sure you could use it as a drag brake, stopping brake, whatever, and it would cope just fine.
Stefan-Boltzmann Law:
q = σ T[SUP]4[/SUP] A
where
q = heat transfer per unit time (W)
σ = 5.6703 10[SUP]-8[/SUP] (W/m[SUP]2[/SUP]K[SUP]4[/SUP]) - The Stefan-Boltzmann Constant
T = absolute temperature Kelvin (K)
A = area of the emitting body (m[SUP]2[/SUP])
Note that there is no term for mass. Those of us who've used drag brakes much realize that they come to a constant operating temperature fairly quickly. Once there, heat dissipation is governed by the Stefan-Boltzmann Law. Note that area is a term in this equation. That's why larger discs work better - not because they have more mass, but because they dissipate heat more quickly.