You'd be in pre-78, most of the time (it would be possible to modify a 74 model bike so it didn't meet
both the pre-75
and pre-78 rules).
I read the comment about not wanting pre-75 bikes to run in pre-78, and thought that it refered to bikes that were clearly pre-75 legal (or would need minimal, small mods to make them pre-75 legal).
If nothing else, the class is "pre-78", not "75~77". Fair enough that at the Nationals you're limited to only the one age class per bike, but there's nothing in the rules to stop you riding a pre-65 bike as an Evo,
if it was the only class you rode that bike in.
I've heard of the road-race guys having two different fairings for one bike, which makes the bike legal in two different eras - the historic road race rules specifically say that a bike will be defined by its newest major component. So changing to a later major component between races, instantly makes the one bike legal for both classes.
Not sure if I agree with the intent in that case, but I can't argue with the execution.
Conceivably, you could swap front wheels (with different hubs
) or rear shocks (with more travel) between races to change your pre-75 bike into a pre-78 one.
And a third wheel fitted with a YZ-J hub, would get three classes from the one bike.... (although a pre-75 bike is gonna get snotted in a field of pre-85 bikes).
