Originally Posted by
BoraxKid
This passage is especially interesting to me:
https://cyclingtips.com/2020/07/bicy...-to-stop-them/
So it seems that this issue of speed wobble is much more likely to happen on those older, vintage steel frames that certain people gush over, and it's much, much, less likely (though still possible) to happen on a newer, carbon-fiber frame (aka "plastic bikes" as the retrogrouches like to say). I wonder if we'll ever see a manufacturer posting a warning label on a frame to indicate its Hopf bifurcation predicted speed at which wobble becomes a safety concern. Maybe the marketing departments can start touting how fast their company's bikes can go before they start to wobble? Or would people take that as a challenge? Interesting topic, indeed!
Not sure I agree with that. It’s a classical mechanical resonance or under damped issue where some repetitive frequency at the right frequency sets up the wobble. Depending on what’s wobbling - top tube, fork, chain stay etc... you need to damp that member. That’s why often clamping the top tube with your knees stops the wobbling because you’re changing the frequency that that member resonants at which happens to be related to the speed you’re traveling (or, more accurately, to the wavelength of the frequency). That’s also why speeding up/slowing down can help or moving your weight placement. The problem with braking is that it can increase the amplitude of the oscillations until you slow down enough to get out of the resonant/under damped frequency range. The problem with speeding up is that you eventually need to pass through that slower resonant frequency range at some point. So it’s a tricky problem and needs to be solved because if you hit it just right the amplitude of the oscillation can increase rapidly to the point of it being uncontrollable. “Uncontrollable” means to the point it’s not possible to control regardless of your bike handling skills.
So one does need to try and find the cause of the wobbling. All the advice on checking hubs, head sets, etc... are valid. And often the solutions are counterintuitive because they are frequency/wavelength related more than anything else.
That said, it’s possible to create a frame out of pretty much any material that hits resonance. I have a stainless steel frame that I’ve never seen it wobble. I used it for light touring because my other bike wasn’t available at the time, with a light load of less than 20lbs extra on the frame, I would get a pretty severe wobble at around 14-15mph. Took the weight off and it was fine and has never been an issue since. That’s why any frame can wobble under the right conditions.