# How does a “tank slapper” occur? Why wouldn’t a motorcycle simply fall over instead of having the wheel wobble from side to side?

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How does a “tank slapper” occur? Why wouldn’t a motorcycle simply fall over instead of having the wheel wobble from side to side?

In: Engineering

I thought they were called “speed wobbles”….but maybe that’s just bicycles

Pretty sure it’s a sudden and catastrophic change in the center of gravity which can’t be resolved.

Centrifugal forces keep the bike upright as does the body acting as a counter weight

Do you mean the death wobble?
Well because conservation of momentum. Also, the bike *does* fall over if they get bad enough. The natural way a bike rolls is straight, and the wheels *really* want to go straight, so unless you get some serious wobbles where the entire center of mass gets shot one way or another very quickly, you can usually recover from it by just slowing down.

Partly because of the rake of the forks. The wheel can rotate left to right, but only around the axis of the front forks.

But, uh that’s all I recall.

A motorcycle wants to go straight. It will naturally correct its course by going to opposite the direction that would cause it to fall over.

So if there is sudden traction with the handlebar turning to the left, the bike will lean the opposite direction, which will inevitably turn the handle bar far right to counter. Which, inevitably makes the bike fall to the left, which then will jerk the handlebar far to the left.

This occurs if coming down from a wheelie and the front wheel was turned to one side. This also occurs if the front wheel hit a pothole or a bump while turned.

Usually a tank slapper will resolve if you speed up the bike.

The wrong move to do, as a rider, is to try to counter the tank slapping by trying to hold on to the handlebar harder. This will transmit the oscillation to the rider, which will transmit the oscillation to the body of the bike, further causing instability and ultimately a crash.

A bike, when encountering a tank slapper, will generally resolve itself if the rider relax on the handlebar, and speeding up. If speeding up is not feasible, then, letting go of the handle bar completely can resolve the tank slapper.