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DC Crew
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Here is a link, but the good text is below. This is some REALLY good info.... covers drilled/slotted rotors.

A big thanks to Ray "RT66Z06" for having a big brain and sharing this.:thumbsup:

http://www.digitalcorvettes.com/forums/showthread.php?s=&threadid=295


In 1995 Chevrolet included RPO J55 "Heavy Duty Brake Package" on all models. Previously it had only been available with RPO Z07 and RPO Z51. Source: Corvette Black Book 1953-2002 pp 102. The brakes on the 1996 GS were RPO J55 with black-painted calipers and Silver "Corvette" lettering. Source: Corvette Black Book 1953-2002 pp 105.

Road tests which include braking data are all over the map in terms of braking distance since each tester has different reflexes, the sufrace conditions and temperature vary, and the condition of the vehicles and tires vary dramatically. This is componded by the fact that some rags (er, sorry, magazines) test from 60mph, while at least one tests from 70mph. I have seen a high of 121 feet from 60mph to a low of 104 feet from 60mph.

Believe it or not, braking distance in cars today is more a function of the grip of the tires, the amount of brake bias, the amount of weight transfer, and not a function of the brakes themselves.

Practically every car produced today has disk brakes capable of easily locking up all four wheels because the tires are, beyond a certain limit, unable to handle the decelerative forces and will begin to slide. Sliding friction is not as high as rolling friction so a sliding tire produces less decelerative force than a rolling one. That is a secondary reason for having an ABS system.

The primary purpose of ABS (contrary to popular belief) is to permit the tire to brake (threshold-braking) while turning. Braking introduces one set of forces into the tire, while turning introduces a second set of forces. The tire can usually handle both up to the limit of adhesion, at which point the tire stops rotating. ABS senses the reduced rotational speed of a tire/wheel in this situation and reduces the brake pressure to that caliper by allowing brake fluid to bypass the caliper and return to the master cylinder. This reduces the decelerative force on the tire to the point where it will continue to roll while still dealing with the turning force induced by the steering.

Braking on the street or drag-strip is much different than braking in autocrossing or road racing. In these environments the problem is not so much braking ability as it is brake fade.

Brake fade is caused by several different things all initially caused by heat. The brakes slow the tires, the tires stop the car. The brakes convert the kinetic energy of motion into heat energy. That heat must be disappated, and in autocrossing or road racing it must be disappated quickly.

The primary cause of brake fade in a stock vehicle is boiling brake fluid. The brake pads generate friction when they squeeze the rotor. The rotor gets hot, the pads get hot, and that heat is transferred to the caliper. The brake fluid runs through the calipers and picks up heat. It can eventually pick up so much heat that it will boil, producing gas bubbles. Gas is compressible, hydraulic fluid is not. When the gas bubbles compress they produce a mushy-feeling brake pedal. In extreme situations the brake pedal will go all the way to the floor and the vehicle essentially has no brakes. Changing to a brake fluid with a higher boiling point will help a great deal (e.g., Motul 300 C, and it takes one and one half cans to completely flush the brake system of the old fluid).

Another cause of brake fade has to do with the pad surface. Some compounds actually melt and produce gas or liquid which acts as a lubricant between the pad and the rotor. This problem can be ameliorated or eliminated entirely by slotted or cross-drilled rotors. The slots or holes allow the gas/liquid a place to escape to so that it no longer remains between the pad and rotor. Cross-drilled rotors must have the holes chamfered to reduce (it can't be eliminated) stress cracking of the rotor around the holes.

Vented rotors have curved vanes which radiate out from the center of the rotor. Their pupose is to dissappate heat from the rotor. Some owners confuse vented rotors with cross-drilled or slotted rotors.

Getting cooling air to the braking system goes a long way towards disappating heat. The front brakes perform the overwhelming proportion of braking so they get hotter. The C5's brake cooling vents in the front help but need to be augmented for road racing. The rear brake cooling ducts on the Z06 are a nice visual addition but do little since the rear brakes (on front engine cars) do relatively little work, even in a race car. That's why all cars have a brake bias valve and a brake proportioning valve. The rear brakes actuall apply slightly before the fronts (while there is still weight over them) and pressure to the rears begins to be reduced as weight transfers to the front suspension in order to avoid rear-wheel lockup (bad car, produces oversteer on corner entry, felt as "twitchiness" at the rear).

Baer racing produces cross-drilled rotors with chamfered holes and an anodized finish to prevent rusting when they get wet (the rust gets sanded off the first time you apply the brakes but it's visually unappealing).

Many companies produce brake pads with compounds that resist melting (e.g, Porterfield Racing) made from a variety of materials including carbon-Kevlar but be aware that they generally squeal when cold and produce prodigious amounts of brake dust which is corrosive if left on the wheel too long. Caveat car-nut.
 
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