Tank slap, general comments

[desmo796]

Tank slap seems to be an issue with various models, years, and manufactures of bikes that primarily do not come standard with a steering damper.

There are a wide range of riding styles, and physical builds. With those influencing factors, along with the set up of the bike (original factory build),
it seems one needs to follow a method to make adjustments to work out the slapper kinks.

Tank slap may not be a "know" issue with new bike purchasers/riders. We could go into an analytical critique as to why manufactures do not
put more effort into making tank slap less of a problem, though IMHO they should provide general information of this phenomenon to new bike purchasers.

This is not to say that the manufacture is omitting to a problem in providing such info, however when I read about this issue from those with a new bike,
is it always something the new owner has done to cause this such as how they react to the event. Then why is it happening?

I heard a story last weekend where the rider went down. What initiated that was tank slap. This was an individual relatively new to motorcycling.
So I ask the question, when buying a new bike is tank slap something an owner should be made aware of rather than learning about it during a ride?

I do not know all the details of the incident, and there could have been operator inputs that may have influenced the mishap. I know that I have experienced this on my HYM796.

Steering dampers are not the be all end all though they do offer a good option to help greatly reduce the occurrence. I wonder why steering dampers are not standard on all bikes.

Manufactures and magazine ride reviews must experience tank slap to some extent during development/reviews right? Perhaps I'm wrong, or rather its not great enough of an issue to report?
My riding experience is extensive across various riding environments where I was enlightened many yeas ago about this. Lately I've seen a higher frequency of riders complaining of tank slap.

thoughts / opinions

D796

[speirmoor]

I think its because its not an exact science is the problem.There are too many variables involved such as riders weight,suspension settings,riding style that tank slappers can be not guaranteed to happen.

[Birbusa]

I've had this happen to me on my Hayabusa before although I would'nt call it a tank slap it was just "head shake." It went away when I had the front suspension sorted.

[dww257]

Originally Posted by Birbusa

I've had this happen to me on my Hayabusa before although I would'nt call it a tank slap it was just "head shake." It went away when I had the front suspension sorted.

Good distinction, head shake even vigorous head shake is one thing, a true slapper is something else again. Ergo "this is interesting need to work on it" as opposed to outa the seat sprained wrists "Jesus this might be the big one".
One time long ago whilst doing a hand stand on the bars noticed smoke coming off the front tire each time it touched the ground after alternately hitting each steering stop. Did not have a get off, somehow. That was the worst but there have been others.

[alpha17c]

I've had a pretty good head shake. Enough to feel like my helmet was slapping me in the face. This was on a Yamaha R1 with sorted suspension and a stock steering damper. I purchased a Ohlins damper. I never had the issue again.
If it had something to do with it or not I don't know. I've had a similar feeling however it corrected quickly with the Ohlins damper.
I feel it never happened again because of a quality damper. Worth all the money.
Has anyone noticed that the Motogp bikes have the damper slider coated like the forks. Just thought that was cool

[stryder]

Where would it end, the manufacturer's responsibility to inform riders of potential riding dangers? Have you never heard the term "caveat emptor"?

'nuff said.

[dmrst]

if you slap your tank, will it swell?

Sorry, it was just lying there...

[jcns]

I am a believer of personal responsibility and accountability.
You want to buy any device, it's your responsibility to get educated, trained, and learn the risks, the advantages, the disadvantages, how to use it, how not to use it, what to never do, etc.
If you want to blame somebody, you should blame your parents for failing to teach the very basic values of "It's your life, you take care of it".
Motorcycles, as everyone on this board knows, has been, can be, will continue to be a very risky and sometimes deadly device.

[pjonte]

Tank slap and head shake occur under different conditions. Slappers always start with head shake and can under certain conditions accelerate very quickly to full blown lock-to-lock slapping. Imagine stand riding on the back of a shopping cart as the front wheels start to caster (shake). This is because of insufficient trail and the front wheels are very lightly loaded. The side forces acting to rotate the wheel around the steering axis vs forces straighten it by the trail under light loading to are almost equal, the wheel does not know which way to steer so it oscillates wildly finding its natural frequency.

For sports bikes, trail is a trade-off between ease of handling and stability. Ever wonder why your bike "stands up" under front braking into a corner? The front end is under heavy load from deceleration and additional weight has shifted to front as the forks compress. Even modest trail will easily exceed your counter steering efforts causing the bike to straighten and stand up.

Motorcycle head shake is caused by exactly the same forces as the shopping cart. Light frontal loading from hard acceleration or the road dropping away coupled with light trailing geometry. Dampers can help to arrest the oscillation by damping the forces and shifting the natural frequency of the steering to a frequency much lower than the system can naturally sustain.

Full on tank slapping is a extreme case, and is usually assisted by rider inputs. Head shake frequency is generally to fast for the "normal" rider to arrest by applying counter forces to the handle bars or to manually damp. Instead the rider usually winds up applying counter forces which are lagging the required response time reinforcing the head shake as the rider applies force in the same direction as the shake vs counter direction as intended. Or manual damping inputs applied by the rider positively reinforces the head shake. With these assisted inputs, in as little a few cycles the slap starts to hit the steering stops as it literally starts bouncing between them. At this point its all over with but the crying, the best coarse of action would be to release the handle bars all together and grab hold of the tank. Prior to this point of no return, the rider should be lighting up on the handle bar grip, releasing the throttle to load the front end.

A slight head shake under heavy acceleration or the road falling away is completely normal but if you start to feel it in the chassis its time to loosen your grip and let up.

[badass916sp]

Originally Posted by stryder

Where would it end, the manufacturer's responsibility to inform riders of potential riding dangers? Have you never heard the term "caveat emptor"?

'nuff said.

Agreed Stryder.

There is no way in hell you're gonna get a slapper or wobbler when riding in s straight line within reasonable speed limits.

Now, if you ride a 1992 gsxr 1100 with a 50 tooth rear sprocket and thwack the flatsides aggressively in a slight bend in the road and hit a bit of uneven pavement, you definately will get a tank slapper.