Disc brakes were originally developed for race cars. Everyone knows that race cars move along at high speeds -- but they also need to decelerate rapidly. In the early days of racing, when most cars were equipped with drum brake systems, brake fade led to a number of on-track mishaps. Disc brake systems were better ventilated, and as a result, reduced some of the stress that racing and excessive heat
build-up can cause -- in turn, reducing (but not eliminating) brake fade. In time, these powerful brakes trickled down to less performance-oriented vehicles. Now, they're even found on most economy cars. Nonetheless, high-performance cars are still a major market for better and more powerful brakes, and variations on the basic brake caliper design help these brakes provide superior stopping power.
There are certain limitations to just how much the vehicle's brakes and its calipers can do to stop a vehicle; while they may be able to bring the wheels to a stop, it's up to the gripping power of the tires to do the rest, and improved brake parts can't help beyond a certain point. However, there are several ways in which brake calipers can be (and have been) improved. Some common features found in performance brake calipers include:
- Bigger pistons -- The larger the pistons are, and the greater the area over which they come in contact with the brake pads, the more clamping force they have on the rotor.
- More pistons -- Low-end floating brake calipers have a single piston, on the inboard side. Low-end fixed calipers have a single pair of pistons, flanking the rotor disc. High-performance calipers can have multiple pins or pairs of pins, mounted on opposing sides of the rotor. Six-piston models are increasingly common and even 12-piston models are not unheard of. Increasing the number of pistons also serves to increase the clamping force of the caliper.
- Less heat retention -- In a sense, your brakes can be thought of as a device for converting movement into heat. As the vehicle slows down, all of that kinetic energy has to go somewhere and most of it ends up as heat. If you want to look at it another way, all that friction between the brake pads and the rotor generates heat in much the same way that striking a match generates heat. If too much heat builds up, the brakes begin to fade, or become less effective. So, the better ventilated the brake calipers are, the better they perform. Also, the larger the surface of the brake rotor, the more the heat is spread out.
- Differential bore calipers -- As the surface of the rotor heats up, the clamping force of the pistons has to be increased to avoid brake fade. If the caliper has multiple pistons (or multiple pairs of pistons), the brake rotor surface is initially heated by the pistons pushing against the brake pad at the leading edge of the caliper, making the rotor surface hotter when it rotates back to the pistons closer to the trailing edge of the caliper. Therefore it helps if the pistons closer to the rear edge of the caliper are larger. Differential-bore calipers use smaller pistons up front, larger pistons toward the back.
All of these technologies can increase the braking power provided by a caliper. For smaller cars that typically aren't driven at high speeds, this extra braking power isn't really necessary. However, the faster and more powerful a vehicle is, the more it will benefit from high-performance calipers.
There's no need to stop now. The next page is loaded with lots more information about braking, brake calipers and other related topics -- just follow the links.