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      11-06-2012, 06:08 PM   #72
Brigadier General

Drives: 130i
Join Date: Nov 2011
Location: QLD, Australia

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Originally Posted by MteK
Originally Posted by GaryS View Post
Well, I agree with most of that with some small quibbles.

Resistance to fade depends mostly on the choice of pads. Better ducting can help some, and better rotor design can help a little.

Heavier rotors absorb more heat, and fancy rotor designs can dissipate heat faster, but bigger rotor diameter and width by themselves have no effect on heat.
Here is some interesting info I found in regards to rotor design. Also, having a larger lever (e.g. caliper further away from the pivot point) increases torque and reduces the amount of energy used to stop the rotation. Less energy = less heat.

-The brakes function by converting the kinetic energy of the car into thermal energy during deceleration - producing heat, lots of heat - which must then be transferred into the surroundings and into the air stream.

- The amount of heat produced in context with a brake system needs to be considered with reference to time meaning rate of work done or power. Looking at only one side of a front brake assembly, the rate of work done by stopping a 3500-pound car traveling at 100 Mph in eight seconds is 30,600 calories/sec or 437,100 BTU/hr or is equivalent to 128 kW or 172 Hp. The disc dissipates approximately 80% of this energy. The ratio of heat transfer among the three mechanisms is dependent on the operating temperature of the system. The primary difference being the increasing contribution of radiation as the temperature of the disc rises. The contribution of the conductive mechanism is also dependent on the mass of the disc and the attachment designs, with disc used for racecars being typically lower in mass and fixed by mechanism that are restrictive to conduction. At 1000oF the ratios on a racing 2-piece annular disc design are 10% conductive, 45% convective, 45% radiation. Similarly on a high performance street one-piece design, the ratios are 25% conductive, 25% convective, 50% radiation.

-Repeated hard stops require both effective heat transfer and adequate thermal storage capacity within the disc. The more disc surface area per unit mass and the greater and more efficient the mass flow of air over and through the disc, the faster the heat will be dissipated and the more efficient the entire system will be. At the same time, the brake discs must have enough thermal storage capacity to prevent distortion and/or cracking from thermal stress until the heat can be dissipated. This is not particularly important in a single stop but it is crucial in the case of repeated stops from high speed
Just on your point 1 for now, more torque isn't less heat, it's more POTENTIAL heat per unit of time.

Ie, it turns kinetic into heat faster is all

It's simple more braking force, not cooling/heat dissipation.