What constitutes a motorised bicycle and what constitutes a motorcycle. I've looked at some race videos and want to ask questions. As a new member, I might have something to say which may already have been thought of, but I'll throw it in anyway. All sports evolve and, currently, what I see racing are motorised bicycles. It would be extremely easy for evolution to turn them into analogues of the early racers, with longer wheel bases, improved engines etc. If it's important to retain the bicycle-ness of the machines, would it be appropriate to suggest instituting a rule that limits the maximum length of the bikes, and a have minimum frame height? In addition, perhaps minimum wheel diameters and maximum tyre sections? If it's all been talked about before, ignore me and carry on as usual.