Bonneville America Forums Forums Rider Safety Forums Riding Technique Tank slap

Years ago as I was riding across a particularly rough stretch of road, the bike started to tank slap. My only recourse during that scintillating 1 or 2 seconds was to get off. I was 23 years of age at the time, and bounced around fairly well, with no major injuries. At a brittle boned 50, I don't believe I'm as buoyant anymore...

After recently seeing two videos of bikes in the throes of tank slap, I wondered, aside from the popular emergency correction technique of "HOLY SH-- HANG ON!!!! is there any technique or specific way to correct and regain control of a bike when this happens?

For those who haven't witnessed the pure joys of tank slap, this is what it looks like
http://www.youtube.com/watch?v=LZ1srcQMa_0&feature=related
When it happened to me, it was as if all was well in one second, and in the next second a 500 lb road devil had jumped aboard and had a hold of the handle bars. Not fun.

I also wonder what causes it? I assume the rough road I was on and my vehicle speed at the time was the catalyst, but beyond that, it's a mystery. Is it having a wheel as a gyroscope mounted on the end of what is essentially a spring & hydraulically loaded tuning fork? Whatever it was, I don't want to go there again anytime soon.

It is the harmonic balance being interrupted where the weight is removed from the front wheel. It is usually associated with improper front suspension setup. Soft rubber, too much rake, worn out springs can do it to a conventional bike.

In racing is comes when a rider leaves a curve and hits the throttle hard. When the front lifts and the bike is not all the way straight all the energy is turned into a wobble. The worst thing he can do is hit the front brake. Holding on and tapping the rear brake to take off speed is his only hope. Most end badly.

It is highly unlikely a modern cruiser could ever suffer from a slapper. They don't have that type of balance and surely have no horses to overpower the front end.

Once his feet came off the pegs he didn't have a chance at regaining control.

I thought it was more of a phenomenon with sport bikes that have a really steep rake and hence are less stable. That's what steering dampers are for, no?

it happened to me on a 10 speed once.

OK so it's a short trail thing, which is another side effect of the steep rake of a sport bike... I think having wide bars helps too, just because your arms have better leverage over the steering and help dampen such things... right?

It happened to me several months after I bought my Speedmaster brand new. My first reaction was panic and grabbed the handle bars tighter and it was over before I could make any further choices. Scary and I dont know how it happened. the road is bumpy where it happened and I was hooten along

Derek

I guess in a way the wide bars make your driving sort of 'lazy' (they're easier to leverage) so you don't get into that situation as easy. There are some great rake and trail bits on the web. Here's one that talks about using a raked tree to adjust the trail street chopper

i was always told that when a tankslap happens,hit the throttle not the brakes. If u watch the GP riders when they start the wobbles, they dont slow down at all.

Isle of Man TT Tank slapper

Good thing he wasn't wearing shorts & flip flops

Here's a rake-trail calculator that I happend to come across for those into geometry and such.

Rake and Trail Calculator

the hang on method always worked for me on dirt and my old S3. If you can help it, you of course keep your feet on the pegs but that can be easier said than done. Head shake, tank slap, or whatever you want to call it can get pretty f****** violent. It's also important not to tense up when hanging on, have a firm grip and let the bike do it's thing. Trying to muscle it can have a negative effect if your body motion starts aiding the wobble, especially with wider bars (it's like a wrestler using his opponent's body weight to his advantage). Essentially what happens is you create a feedback loop. If you see someone get this in a race and get bucked off the bike, more often than not the bike will correct itself and stay up until it hits something.

Getting on the gas isn't a bad option and totally cutting the throttle can have a negative effect by slowing the back tire so much that it skips, causing the bike to high-side. Hitting the brake can have the same effect. Whether you ease off the throttle or get on it be easy with it.

As with anything, the correct thing to do is situational dependent. If you're going through a corner and get head shake, then you should accelerate as smoothly as possible through the turn. Decelerating will cause the bike to want to stand up and head for the outside edge of the corner. If you're on a straight road with plenty of room I would probably decelerate slowly and remain calm until it stops.

2 years ago I compression fractured two vertebrae because of head shake, well it was mostly my fault. Story: On the S3, passing in a no passing zone (plenty of room for how quick that bike was), on the gas on a bumpy road, the front was light, hit a bump, and suddenly head shake from ******. I eased off the throttle and held on and it began to straighten out but I still had the car to get past before I ran out of room so I got on the throttle again and the same thing happened. With the blind corner approaching fast and the bike wobbling like a 10 yr old with A.D.D. and on crack, I picked the lesser of three evils (1. attempt to ride it out and hope nothing was coming around the corner 2. not be able to ride it out and get run over by the car I was passing 3. take my chances with the berm) and 150 ft. through the air, a totaled S3, and a broken back later, the ambulance was on it's way. I still pay for that accident every day but at least I'm alive and riding again.

The point of that story is that it has been my experience that getting on the gas will not always save you. I am, however, a true believer in Gary Bailey's philosophy of "when in doubt, gas it".

I hope this helps some of you, and if anyone has any differing opinions I would be more than happy to discuss them as there seem to be many different ideas of how to handle this problem.