What actually CAUSES a tank slapper?

[misti]

This question is inspired by the thread discussing speed wobbles.....

I often hear people talk about tank slappers and speed wobbles and while they are good at giving tips and advice on what to do if one happens to occur there is little info on what actually causes a tank slapper or speed wobble.

So, what causes them to happen and what are the typical things that riders do that increase the chances of experiencing them?

Misti

[Brainfry]

Originally Posted by misti

This question is inspired by the thread discussing speed wobbles.....

I often hear people talk about tank slappers and speed wobbles and while they are good at giving tips and advice on what to do if one happens to occur there is little info on what actually causes a tank slapper or speed wobble.

So, what causes them to happen and what are the typical things that riders do that increase the chances of experiencing them?

Misti

Never experienced one, (knock wood). But it's my understanding that when the front tire lifts under acceleration and it's not inline with the bike/track/road... when it returns to the pavement it begins to "auto correct" itself back in alignment and causes the bars to slap from side to side until it "hopefully" gets back on track. Am I close? And a properly adjusted suspension and a rider weighting the front end could "possibly" help to avoid such an occurrence from happening... yes? No?

B

[DrIoannis]

Well as explained that is how it starts.Then our hand take over and things get worst.We actually accelerate the tank slapping when we apply force to the handle bars to "stop" it.Relax and things will go better...

[KrautBurner]

From what I have read it relates to the gyroscopic effect of the front tire trying to find center( auto correct ) but it oscillates too far. Basically when you are riding straight and both wheels are in line the bike will continue that way unless something is done to change the wheel track, like turning the bars. When you let got the wheels try and come back into line. If that happens too fast they can over correct and then they over correct back again but a little less. This continues until they come back into line. Sometimes they go into harmonic oscillation and the effect is magnified and it takes a good while to auto correct but most times you just have to relax and hold the bars loosely and let the bike correct itself. The steering damper ( hidden in the faring on the RR ) helps to reduce the violence with which the steering head moves and lessens the 'tank slapper' effect. Four wheel drive trucks use the same thing on the steering to keep ruts in the trail from ripping the wheel out of your hands. I would have to look up the exact definition but this is my understanding of why it happens. Lifting the front wheel off the ground in a wheelie and setting it down out of line just makes it happen very quickly. The more out of line you set it down the greater the effect.

[Stockholm]

YouTube - Terrible Bike Crash

[mateo]

A few days ago on the highway,i pick up a screw with my rear tyre and tyre started slowly flow the air.Speed were about 260 km/h ,motorcycle is started shaking like wild buffalo,i stopped after few hundred metres,happy to have pulled out alive.I was scared like never before.

[misti]

Originally Posted by KrautBurner

From what I have read it relates to the gyroscopic effect of the front tire trying to find center( auto correct ) but it oscillates too far. Basically when you are riding straight and both wheels are in line the bike will continue that way unless something is done to change the wheel track, like turning the bars. When you let got the wheels try and come back into line. If that happens too fast they can over correct and then they over correct back again but a little less. This continues until they come back into line. Sometimes they go into harmonic oscillation and the effect is magnified and it takes a good while to auto correct but most times you just have to relax and hold the bars loosely and let the bike correct itself. The steering damper ( hidden in the faring on the RR ) helps to reduce the violence with which the steering head moves and lessens the 'tank slapper' effect. Four wheel drive trucks use the same thing on the steering to keep ruts in the trail from ripping the wheel out of your hands. I would have to look up the exact definition but this is my understanding of why it happens. Lifting the front wheel off the ground in a wheelie and setting it down out of line just makes it happen very quickly. The more out of line you set it down the greater the effect.

This is a pretty good explanation, I just want to clarify something you said. You mention that the bike is stable and will continue following a line when the bike is riding straight but that if something is done to change the wheel track, "Like turning the bars," that the bike might try to auto correct.

Turning the bars won't initiate a tank slapper and the wheel won't try to come back in line if you have just turned the bike. It takes a greater force, like if you come down crooked after a wheelie or hit a big bump while leaned over that is going to initiate the auto correct response from the bike. Riders holding on too tight will also prevent the bike from auto correcting in this situation.

You guys mention relaxing on the bike but that can be pretty freekin hard to do when the bars are going from side to side in a frantic manner. What can you do with your body to help ensure that you are able to relax your arms and not strangle the bars?

Misti

[S1KBEEMRR]

Originally Posted by misti

You guys mention relaxing on the bike but that can be pretty freekin hard to do when the bars are going from side to side in a frantic manner. What can you do with your body to help ensure that you are able to relax your arms and not strangle the bars?

Use the lower half of your body. Grip the tank with your legs (outside leg if in a turn), and weight the pegs.

[Mack]

Happened with my grocery cart yesterday too. The ensuing cart slapper marked their newly shined floor up pretty good too when it oscillated.

I just can't race the damn things like I used too to the shortest checkout line no more.


Mack

[S1KBEEMRR]

Originally Posted by Mack

Happened with my grocery cart yesterday too. The ensuing cart slapper marked their newly shined floor up pretty good too when it oscillated.

I just can't race the damn things like I used too to the shortest checkout line no more.

LOL, sounds like the carts need a better steering damper. They need to issue a recall.