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By Bill Holland
Disc brakes — or rather the merits of carbon fiber brakes vs. conventional steel rotor setups— has been a hot topic as of late. Newly enacted NHRA rules requiring carbon/carbon brakes on nostalgia fuel cars has promulgated an outcry from many racers. And while there are two sides to any story, before we get caught up in a heated discussion about carbon fiber vs. steel, there are some other safety issues that should be addressed.
According to Mark Williams, who has been manufacturing disc brakes for drag racing applications since the late 1970’s and for the last several years been the only NHRA Major Sponsor posting for brakes, the single most important problem with any brake system is not having sufficient fluid volume and line pressure. Imagine if someone stuck a block of wood under the brake pedal of your street machine and you could depress the pedal only partially. Needless to say, the time it took to stop the vehicle would be far greater than normal. When there isn’t sufficient line pressure for the pistons in the calipers to clamp the rotors forcefully stopping distance is significantly compromised. What’s more, this also causes a major heat build-up that can lead to the rotor warping or cupping —leading to a whole other set of problems.Achieving the desired brake line pressure (Mark Williams recommends a minimum of 1000 PSI for normal operation and1200 PSI for severe braking) is a function of how much force can be exerted on the master cylinder pushrod and the size of the master cylinder itself. Since most of us don’t look like the participants in “The World’s Strongest Man” contest (and it’s doubtful if any of them could exert the direct force needed to get 1200 psi) all car builders must look back to the teachings of Archimedes and resort to using mechanical leverage to obtain the necessary multiplication.