Brake Upgrade - Stop It!

A Little Extra Padding
Though a big-brake kit's massive rotors and multi-piston calipers generally hog all the attention, brake upgrades actually come in many shapes, sizes and-luckily for most of us-budgets. Remember Chen's comment earlier about keeping an upgrade proportional to a car's performance level? For many, a simple brake pad upgrade will provide all the braking boost you need.

Pad technology is complex enough to warrant its own article, so we'll try to keep it simple. The two main characteristics you're looking for in a performance pad are its temperature range and coefficient of friction. Several brake companies, such as Endless USA, Mintex Racing, and Wilwood, provide pad-specific temperature and friction coefficient data on their Web sites to help you choose the right pads for your application.

The pad's temperature range is just that-the operating temperature at which it provides its optimal grip. If you're looking for a track-day pad with resistance to fade at high temperatures, this is a telling factor. But you need to watch the other end of the range, too, especially if you're upgrading a street car. If you live in Wisconsin and choose a pad that works best between 30 and 700 degrees Fahrenheit, that first stop on a winter morning could be more thrilling than it should be. Temperature range is one of the biggest reasons why you shouldn't run race-level pads on the street.

The pad's other characteristic, friction coefficient, is a good indicator of its initial "bite," said Chen. In general: the higher the number, the stronger the bite. But also pay attention to the pad's coefficient rating range. "Friction coefficient is sort of like a bell curve," he explained. "It's not linear through the temperature range. The first number indicates what the pad's initial bite will be, and the second is what it will top out at, not what it will reach at the end of the range, but the highest it will reach." The narrower the coefficient range, the more consistent, or predictable, the pad's bite will be throughout its temperature range.

Rotor rooting
Combine a pad upgrade with new brake rotors and braking performance takes another jump.

"We talk to people in terms of good/better/best upgrade options," said Stillen's Bernal. "At the 'Good' level we recommend the original calipers with a higher heat-range pad and original-size rotors, but rotors that are heat treated, possibly cross-drilled or drilled and slotted. It's a pretty low budget step up; in some cases it's no more expensive than going to dealer and getting replacement parts there."

The slots in a rotor's face (also called slits by some companies) are there to shave the face of the brake pad, helping to "keep the pad faces free of burnt compound elements and help to prevent pad glazing," said Wilwood's Bush. Added Brembo's Valskis, "Rotor slots can also lead to increased disc life. Because they continuously clean and refresh the brake pad surface, the pads won't harden" and wear the rotor surface.

And then there's rotor cross-drilling, one of the biggest areas of disagreement there is among brake companies. Drilling a rotor was originally intended to lighten it for racing applications, and to provide an outlet for gasses that were vented by certain types of racing brake pads as they got hot. Like slotting, cross-drilling does some pad-face cleaning. Beyond that, the benefits of drilling are hotly contested.

There are, however, other rotor design characteristics that provide definitive performance benefits that all our experts agree on. One is to step up from a one-piece iron rotor to a two-piece rotor with an iron disc that's mated to a hat or bell-which mounts the rotor to the hub-made of a lighter material, such as aluminum. This design reduces the rotor's overall weight, which lightens the car in a critical area, since rotating mass is several times heavier than stationary mass. Using aluminum for the hat also helps protect the wheel hub from heat damage, as aluminum dissipates heat better than iron.

The biggest advantage to a two-piece rotor, though, is that it allows the use of a "floating" hat assembly, where the hat is held to the disc with clips, pins or some other device that allows "movement radially, toward or away from the center, between the hat and rotor, but keeps them fixed in the direction of rotation," said Barnes. "The benefit is that the rotor expands evenly on both sides, rather than taking on a slightly conical shape, as can happen when the friction surface is heated with one side solidly connected to a hat that is at a lower temperature. Rotor coning can lead to uneven pad wear that will prevent a solid pedal feel and confident on/off response."

Improving pad wear, lightening the rotor and reducing the risk of warpage all benefit overall brake performance. But if what you're after is an increase in actual stopping power, there's only one way to take a rotor: bigger.

Of course, rotor size is ultimately limited by wheel size. And there isn't a hard-and-fast rule about how much rotor you can fit behind certain wheel diameters. "In general, a 17-inch wheel will accommodate up to a 332-mm (13.1-inch) rotor, a 355-mm (14.0-inch) rotor will require an 18-inch wheel, and a 380-mm (15.0-inch) rotor needs a 19-inch wheel," said StopTech's Barnes. He was the only one of our experts who would commit to any kind of size estimate.

So how do you figure how large to go with your rotors? Check with your brake retailer first, as he or she may have first-hand experience with your wheel application. If that's not the case, many brake companies offer downloadable templates, made from CAD drawings printed to scale, that you can hold up against| the inside of your wheel to check fit. And remember, like many other performance items,bigger isn't always better when it comes to rotors. "In general, rotor size should be determined by the energy absorption and dissipation requirements the vehicle places on its brake system," said Barnes. "If you choose a rotor larger than is required, its greater mass will make the car slower."

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