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Where the list gets tricky is when a manufacturer has to pony up for a bike that might not be raced by anyone—or typically by only one rider. For example, the Husqvarna TC125 two-stroke has been paid for and homologated so that Gared Steinke could race it in the 2016 Nationals. Note that Yamaha has not homologated any of their two-strokes, while Husky and KTM have paid for both of their 125 and 250 two-strokes.
We are kind of confused as to why any 250cc bikes are legal in the 450 class in Supercross. The last bike that Ryan Dungey would want to come up to lap over a triple is a guy on a bike with 20% less power. This must be one of the AMA’s infamous “Good Buddy RuleS” that the AMA wrote for the Supercross promoters as a hedge against not enough 450s showing up at a given race (and then they could throw a couple 250 guys in to make the gates look full)—or it is for the privateer who doesn’t have a 450 to race (mostly notably Fredrik Noren who raced a CRF250 in the 450 class while waiting for the 250 East to start). The 250s should not be allowed in the 450 Supercross class—for safety reasons.