There is a long-standing debate...
There is a long-standing debate as to which type of caliper is best: cast or billet. It all comes down to the design. The elimination of heat is one of the major goals of the caliper. The open-bridge design allows the heat to radiate from the top of the caliper. Some of the manufacturers are using stainless steel pistons and heat shields, because they do not transfer heat as readily.
The new pad materials are not as detrimental to the rotors. The pad manufacturers are creating friction materials that transfer a little of the material to the rotor. This way, the pad is working against itself and not biting into the rotor. As the materials become better at stopping the car, the pad generates more heat. This is causing the brake pad to develop a taper. As the pad taper increases, less of the pad surface is making contact with the rotor. When this happens, you lose stopping power.
To counter this, the brake manufacturers developed differential-bore calipers. They use a smaller piston at the front of the caliper to decrease the clamping force, and a bigger piston at the rear to increase clamping force. This compensates for irregular pad wear. With a differential-bore caliper, the pads wear evenly and live longer. Obviously, the braking force increases, because the entire pad surface is in contact with the rotor.
The size of the caliper determines the size of the brake pad. Pads that are longer, wider, and thicker dissipate the heat better, and you will get longer pad life. The front brakes on a pavement car do 75- to 80-percent of the braking. The newest brake pads have a higher coefficient of friction. They generate so much heat that the caliper manufac-turers have developed different approaches to keep the heat from transferring through the piston to the brake fluid. Some use stainless steel heat shields to act as thermal blocks. Others ceramic-coat the inside of the caliper and the piston, to insulate the brake fluid from the heat.
If the racer uses a quality competition brake fluid that is good up to 570 degrees F, it should not boil under normal racing conditions. The bigger problem is the piston O-rings. Although these are high-temperature O-rings, they are only good for around 300 degrees F. If you have a brake rotor that is running 1,000 degrees, it is very easy to have the caliper run 300 to 400 degrees.
That heat is transferring from the brake pad, through the piston, into the caliper, and is deteriorating the O-rings. It used to be you could run 10 to 15 races without replacing the O-rings. Now with the severe heat caused by the better brake pads, the O-rings start to degrade, break down, and stick. This causes the pistons to not retract properly and generate more heat. It is a vicious cycle. Some racers replace O-rings before every race.
For racing, a vented iron...
For racing, a vented iron rotor is best. The vanes are either curved or straight. The curved vanes achieve more surface area than the straight vanes, so the rotor will cool better. A curved-vane rotor will also pump more air through the rotor. The number of vanes, and their thickness, length, and shape vary according to the racer's braking requirements.
When purchasing a rotor, you must consider the temperature range you will be running, and how often the rotor will see heat spikes.
"Rotors are made from three mate-rials. Iron is the most-used rotor material in racing. It is very stable," says Wilwood's Doug Burke. "It operates over an impressive temperature range. We make recommendations based on the operating range, the length of time spent at a continuous temperature, and thermal cycling."
The rotor provides a surface for the pad to work against and to remove heat. For racing, a vented iron rotor is best. You want to have the largest rotor you can fit inside the wheel, because it has the greatest amount of mechanical leverage.
There are two types of vented rotors: straight vane and curved vane. A curved-vane rotor is structurally stronger than a straight-vane rotor. It can achieve more surface area than a straight-vane rotor, so it will cool better. A curved-vane rotor will also pump more air. The number of vanes and their thickness, length, and shape vary according to the racer's braking requirements.