MXA’S AMA RULE OF THE WEEK: THERE IS ALWAYS ONE RULE-BREAKER
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(1) It requires every bike to have front and rear brakes. This rule doesn’t seem to be all that unusual, but at one time AMA dirt track bikes only had rear brakes and, even to this day, speedway bikes have no brakes. The most famous breaker of this rule was ATK, who mounted the rear brake on the countershaft sprocket to lower unsprung weight on the rear wheel. When a rear wheel brake was required by an observant tech inspector, ATK added a rotor and caliper to the rear wheel, but didn’t hook any hydraulics to it.
(2) It stops Ken Roczen from going to the starting line on his Honda CRF450 with drum brakes from a 1980 CR250. Obviously this rule was written when bikes had drum brakes (about 36 years ago) to stop an enterprising team from switching to disc brakes.
(3) It bans carbon fiber, aluminum or titanium brake rotors (and carbon fiber brake carriers). Carbon fiber brake rotors don’t work very well in the low speeds and moist conditions of an motocross track where it is hard to get enough temperature into the rotors to allow the pads to work. Coated aluminum rotors would work in motocross (and in the 1970s there were Harry Hunt rotors in use, but the expansion of the aluminum under high temps often made the coating crack). There are some riders racing with titanium brake rotors at the local level today, but the flexibility of Ti and its poor wear properties don’t make it a good rotor material in a world where the temperatures on the rotor face change constantly and dirt is added to the mix.