Push the brake pedal, and your Porsche stops pretty quickly. Most don't give it much thought if they're just driving around on the street. When used aggressively, especially with repeated laps on a track, stock brake pads can't deliver the same bite when pushed past their temperature limits.
Take a look at what's happening. The brakes turn the rotational energy (of the spinning axles and wheels) into heat by clamping on the brake discs (for those of us driving newer than 1963 Porsches) with the pads. This friction is dissipated as heat, and slows the rotation, which lets the tires do the actual gripping and stopping. There are two kinds of friction. In abrasive friction, bonds between the pad material and the disc rotor are permanently broken and the harder material wears the softer (pads) away. These pads tend to wear quickly and fade at high temperatures. The other type, adherent friction uses deposits of the pad material on the face of the rotor, so at the point of contact, the pad is gripping material spread evenly across the rotor that's essentially the same chemical makeup. These bonds can break and reform. There's no pure form of either of these processes, but different types of pads can use different percentages of each type of friction.
Modern metallic-carbon racing brake pads are more adherent in nature, as are high performance street pads. These pads function well when hot, and are more temperature stable. However, racing
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pads just don't get the job done in a low temperature range - where most street driving occurs.
"When it comes to brake pads, you can't have your cake and eat it too." Tony warns. Drive your stock pads on a track, and you'll heat them up and experience fade, and probably boil the brake fluid. Conversely, if you insist on running racing pads on the street, someone pulls out in front of you and the brakes aren't up to temperature, the car won't stop anywhere near as quickly as street pads. High performance street pads have come a long way, and could be the answer - some have good low temperature characteristics and higher temperature thresholds than stock. On a back road it's always easier to back off a little if the pads get warm, but if they don't work when that garbage truck pulls out in front of you first thing in the morning, it could be ugly. If you're putting your Porsche on the track, it could be time for specific pads for events. Tony can advise you on what pads will suit your driving style, and make your Porsche stop consistently when you need it.
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Above: It's possible to go crazy with brakes on a Porsche 911. The example above is fitted with 962 style rotors and calipers. This particular car, (also running a 962 engine block) is set up for high speed runs like the Silver State Challenge. It runs racing pads.
Left: High performance semi-metallic street pads look very similar to their racing counterparts and offer performance from lower temperatures than racing pads.
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