How Brake Systems Work - CHP How It Works

Industry Brake Experts Explain Rotor Design, Mega Piston Calipers, Pad Compounds, And Brake Alloys

Stephen Kim Jul 27, 2010 0 Comment(s)
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Fixed vs. Floating Calipers
Michael Jonas: "Fixed brake calipers have pistons on both sides of the rotor, while floating calipers position the pistons on the inboard side of the rotor only. The biggest difference between the two styles of design is packaging efficiency, but there are performance differences as well. When you go from a floating caliper to a fixed caliper, you may need as much as two additional inches of clearance near the inside portion of a wheel. As a result, fixed calipers require changing the backspacing of a wheel, which might necessitate stepping up to expensive billet or forged wheels. One drawback of a floating caliper is that it has to activate the inboard side of the caliper before the outboard side. On the other hand, a fixed caliper actives both sides at the same time, so its response time is a little quicker. For most street cars, however, this advantage is negligible."

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Carl Bush: "Floating-mount brake calipers are usually part of an OE compromise for overall caliper cost and wheel clearance. Since floating-mount calipers only have pistons on one side, they can be narrower overall than a fixed-mount caliper. Floating-mount calipers are also likely to move around more, with deflection at the mounting points. Most drivers can feel an improved sense of consistency in brake response and pedal feel with a firmly anchored, fixed-mount caliper. The overall rigidity, and improved pad load distribution of a fixed-mount caliper also has a direct effect on better and more efficient pad wear than a floating-mount caliper, especially those that only have one central piston."

Pad Compounds
Todd Gartshore: "The brake pad is the easiest thing to change in a brake system, and is the most influential on how the entire system works. Think of a pad as the last ingredient that brings everything together that can also be easily tuned. However, just like more cam isn't always better for a street car, a more aggressive brake pad isn't always ideal. The biggest mistake people make is trying to use a race pad on a street car, and even guys with loud exhausts can't handle the noise level of a real race pad. The best pad in a street environment is a pad that has good response but is still driveable. In a street car, having good onset friction is important. Ceramic pads fill that requirement very nicely, but still have enough flexibility to work above 1,000 degrees Fahrenheit. In contrast, most OE applications rely on high-metallic compounds for their low-noise and low-cost characteristics. The downside is they become marginal at 750 degrees. The next step up the ladder from ceramic is a carbon pad, which creates a good deal of friction even at low temperatures. Carbon is more of a race pad, and can survive at temperatures up to 1,350 degrees. However, they require more pedal pressure, wear the rotors out faster, and create lots of dust.

"The old wives tale is that race pads won't work at low temperatures. They may take more initial pedal effort and be harder to modulate until they reach operating temperature, but they still have a higher friction level. The bigger issue is rotor wear. Pads operate through either direct friction or on a transfer film. Most race pads are designed to work with transfer film technology. When a pad reaches 450 degrees and above for a sustained duration of time, a transfer film is created on the rotor surface because of the porosity of the rotor. This reduces the wear rate of a rotor dramatically. Unfortunately, if there isn't enough temperature to create a transfer film or boundary layer, the rotor will wear out very fast. In reality, there is no such thing as a dual-purpose pad. Street driving, road racing, drag racing, circle track racing, and superspeedway racing all require different types of pads. From our experience, ceramic pads are the best all-around compound for the typical hot rod."

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Carl Bush: "Brake pad compounds can vary tremendously, and it's sometimes hard to find just one style of pad that covers all conditions a driver may put his vehicle through. Typically, race pads are formulated to generate higher friction values with more resistance to fade and wear as temperatures increase. Street pads, including high-performance, dual-purpose street/track pads, push the envelope of friction and heat resistance, but also attempt to keep engagement noise and dust to a minimum. Track-only race compounds are generally very aggressive and can provide less than favorable noise and response when used at lower temperatures, such as those observed during normal day-to-day driving. It's best to avoid race-designated compounds for street driving, and pad compounds can have an unbelievable effect on response from your brake system, much like a good tire compound can have a positive effect on traction. Your pads first need to be matched to your temperature operating range, which loosely stated could be street temperatures, intermediate track use, or extreme condition competition. Then, the pad's friction value and response must be matched to your vehicle requirements. Following the pad manufacturer's guidelines and baseline recommendations is usually your best bet, but then feel free to tune with compound changes as conditions may warrant."

Sources

Stainless Steel Brakes Corporation
Clarence, NY 14031
800-448-7722
www.ssbrakes.com
Baer Brakes
Phoenix, AZ
602-233-1411
www.baer.com
MBM Brakes
Ashville, NC 28803
800-231-4125
http://www.mbmbrakeboosters.com
Wilwood Brakes
Camarillo, CA 93012
805-388-1188
www.wilwood.com

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