wphamilton

Seems plausible and may be right, but I have reservations from the beginning assumptions "two reasons: first, there is no periodic forcing that causes the high-speed wobble (in fact, it can happen on a smooth road); and second, there is not a phenomenon that shows a characteristic building of amplitude."

Rider response can be a periodic forcing due to the negative feedback nature, which conforms to the solid advice of releasing your death-grip, or loosening up as I said earlier. In my few experiences there was always a trigger of some sort, and then something that seemed like a periodic forcing input. And it is not clear that there is no "characteristic building of amplitude" - my own experience is that there is?

That said, hopf limit cycles are similar enough to resonance for our purposes, does it really make a difference? Other than academic.