Eli5: Why do speed wobbles happen on bicycles travelling around 40mph or higher?
In: 8
Essentially your bike, as a system, gets into a mode with a resonant frequency. Due to the bike being slightly flexible the forces can cause it to vibrate like a piano string. For this to happen the forces have to be high enough that the frame will actually flex, so it doesn’t happen at low speeds.
It doesn’t happen while pedalling because a changing system doesn’t have a resonant frequency.
[This is a good explanation.](https://cyclingtips.com/2020/07/bicycle-speed-wobbles-how-they-start-and-how-to-stop-them/)
> Data from this latest study shows something less obvious too: oscillations at the seat stays are out of phase with those on the top tube. In other words, when the front of the bike is accelerating in one direction during shimmy, the back of the bike is accelerating in the opposite direction, effectively twisting the bike beneath you.
> The fork, meanwhile, twists slightly upwards in the direction the wheel is facing during shimmy. The handlebar twists downwards in the same direction, creating torsion in the front steering assembly.
Latest Answers