Heat is a blessing and a curse....
Heat is a blessing and a curse. Heat, to a point, increases stopping power. Go over that point and the brakes fade away.
Heat in the braking system is a necessary evil. In order to stop a race car, the brakes must turn the car's kinetic energy into heat energy. This is done by creating friction between the brake pad and the rotor. The more heat the pad can generate, the quicker the car will stop. If you build excessive heat during the race, the brake pads will fade or the brake fluid will boil. In either case, you will lose your brakes and the race.
The key is to know how to maximize braking without producing excessive heat. The proper choice of brake components will allow you to go deeper into corners, and run longer and harder without crashing.
Let There Be Light
The first thing every racer thinks about is getting the lightest components possible. It is true that lighter-weight brake parts will lower the car's rotational weight. This makes it easier to slow down and accelerate the car. It will also lower the unsprung weight on each corner of the car. However, there is a limit on how light brake components can be.
An extremely lightweight aluminum caliper can lose clamping force, because the hydraulic pressure that is pushing against the caliper is trying to spread it apart. Too much deflection in the caliper will result in lost braking force. Instead of squeezing the pads tighter on the rotor, the caliber will bow out when you push on the pedal.
The other detrimental aspect of owning the lightest calipers is reduced heat dissipation. There is simply less material to remove the heat. This causes the brake fluid to boil quicker, which loses braking force. The excessive heat will also cause metal fatigue in the caliper. The front caliper will deteriorate to the point that it will be marginal within two seasons, and will need replacing.
The same thing will happen with lightweight rotors. Less material is available to control the heat, therefore, the pads heat up and glaze over. The extra heat transfers to the caliper and boils the brake fluid. The extreme heat will crack the rotor, forcing its replacement within one season. Lighter is not always better.
The heart of any brake system...
The heart of any brake system is the caliper, the rotor, and the brake pads. Their size is dependent on the amount of heat generated and the length of the race.
Pick up any brake manufacturer's catalog and you'll find a choice of 10 to 20 different calipers. How do you choose the right one for your application? Start with the type of caliper, then look at the piston size, and then the pad size. The last option is the weight.
There are two types of caliper: billet and cast. Which one is best depends on its design. A billet caliper tends to be stronger, but the open-bridge design has a tendency to flex more than cast calipers. On the other hand, some cast calipers are a little more superior, because of their design, than an open-bridge, lightweight caliper. It comes down to the caliper's size, clamping force, and pad size.
Its rigidity and the overall piston area determines a caliper's clamping force. If the caliper flexes, some of the effort that goes into the pedal and down the line as pressure is lost, and not available to squeeze the rotor adequately. Part of the effort is going into expanding the caliper.
The caliper's stopping power is determined by how tightly it grips the rotor. Stopping power is a function of piston area, not pad size. The piston area in the caliper determines its clamping force. To ascertain if a piston area is right for your application, calculate the area of all the pistons on one side of the caliper. The formula is: Area = (piston diameter) 2 x 0.785. (See chart.)
For instance, a caliper with two 1 3/4-inch pistons has an area of 4.8 square inches. The same caliper with two 1 3/8-inch pistons has an area of 3 square inches. The caliper with the larger pistons has 50-percent-more clamping force--even though the caliper is the same size.