How do “Death Wobbles” on Motorcycles/Bikes happen?


In many accident videos they seem to occur without much user input, and my only knowledge on it is that you should not brake if it occurs. Why?

In: 2

Not a physicist, so can’t explain it like you’re five – sorry.

The best I can do is that it seems to be a factor of geometry (front head angle, rake, and trail in particular – although no doubt length spindle to spindle, swingarm length, etc. play into it), the weight of the bike, the the weight distribution / centre of gravity of the bike, the speed, and the acceleration or deceleration it’s undergoing. It’s also worth understanding the idea of counter steering, which in itself is a product of many of the above factors, and I believe contributes greatly to what you describe. (How hard someone grips the bars can even contribute!)

Generally a steeper head angle is twitchier, and this can be mitigated with a steering damper, but that won’t completely solve a tankslapper if it arises.

The best I can offer is that all of the factors above have a complex relationship, and the right (or wrong) mixture can likely set up a harmonic resonance within the steering. I don’t have mathematical proof, however – and I don’t know whether anyone has bothered to find any.