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(1) It bans two-wheel drive motorcycles from being used in AMA motocross or Supercross. This has never really been an issue in these two disciplines, but two-wheel drive bikes can be found in enduros and Endurocross events.
(2) It stops the manufacturers from changing the number of gears—or at least it thinks it does. MXA has tested a number of factory race bikes that rolled off the assembly line with five-speed gearboxes only to be raced in AMA motocross or Supercross as three- or four-speed bikes. Isn’t this illegal? No! For two reasons. First, the AMA rules does not state that the homologated bike must use the stock transmission — only that the “number of gear must be the same as the homologated model.” Second, since there is no clear-cut rule on what defines a five- or six-speed transmission, that means that there is no rule that defines what a four-speed transmission is either.
What does this mean? According to some teams it means that as long as the engine has a five-speed transmission in the cases, there is no rule that says all five gears have to work. Thus, factory teams have been known to build gearboxes that look like they have five-speeds, but only the gear combinations for three or four of the gearsets touched each other. Under the rule, as written, the bike technically has a five-speed transmission, but only a few of them are engaged.
(3) This rule limits the maximum number of gears to six. However, this rule wasn’t always in place and in 1977 Frank Stacy raced a seven-speed Sachs 250 in the Trans-AMA support class. It was the only bike that was ever raced in AMA competition with a seven-speed gearbox. Here is what Frank had to say about it, “The bike came with a seven-speed tranny, but first gear was so low you could climb a wall with it. We blocked first gear out and made it a six speed, but really I could only use 2nd through 6th… 7th was so tall it was geared for the Interstate! We made some good progress in testing and the bike actually started working pretty well, so they said, ‘Lets go racing.’ We picked the 1977 Trans-AMA 250 Support class, which as it turns out was about two weeks from starting. We busted everything out, everyone worked hard and we spent some cash, but we made the first race at Mid-Ohio. I finished 5th in the opener and things kinda went downhill from there. I still salvaged a 9th overall in the series. After the series was over Sachs pulled the plug on the development of the bike. I think they sold some units in Europe, but were basically done in the USA.”