headshake / tankslap

[NiteW4tcher]

in response to the post regarding steering dampers.

before i started riding big bikes, i was given some information on the best way to deal with headshake / tankslaps

first off id like to establish what produces a headshake.....

rapid power delivery? rider error? road conditions? suspension set up? tyre condition? combinations of above???

the information i was given was, to "power out" of the shake....as backing off the throttle will cause the shake to get worse.

and dont ever ride flat out...always have room to accelerate....incase of said headshake


as more experienced riders what are your opinions???


Dan

[Si]

Exactly what I was taught mate. Im quite used to the TL throwing a paddy and shaking her head. Always leave a bit in reserve to pull out of it.

[Mark_Able]

Firstly, by powering out of it, you're taking some weight off the front tyre, therefore reducing it's grip and ability to upset the bike. If you power off, it throws a considerable amount of weight onto the front tyre, giving more grip to the front (as well as steepening fork angle) and so make the 'slapper' worse. Another vital part of correcting a 'slapper' is to stay relaxed. By tensing on the bars and through your body, you'll transfer the violent shaking through to the rear of the bike. The rear is quite happily following it's given course, and it's the rear that's steering the bike, at that moment. Watch the GP riders when it gets all squirrely...

[Squashed_Fly]

Pedrosa is always a good one to watch for that!

[wiltshire builders]

I've met a few people who don't know the difference between headshake and a tankslapper. Just to clear up any confusion, if the bars wobble and you are able to bring it under control, that's called 'headshake'. If you find yourself sliding down the road on your back, that is called a 'tankslapper'. Very few people gain control of a full blown, lock to lock slap.

[Uber Dave]

The biggest learning curve for me was relaxing. Its easier said than done when your brain is telling you to hold on tight as possible and ride it out. But after some time on the R6 and its rather excitable front end it just normal to wind the throttle on and loosen the grip on the bars as well as relaxing your shoulders as well as sitting up to put some more weight over the back end.

I find most of the shakes I get though were caused by bumps in the road but specifically cats eyes, so I now just make sure I miss them when over taking!

[Mark_Able]

I've met a few people who don't know the difference between headshake and a tankslapper. Just to clear up any confusion, if the bars wobble and you are able to bring it under control, that's called 'headshake'. If you find yourself sliding down the road on your back, that is called a 'tankslapper'. Very few people gain control of a full blown, lock to lock slap.

Indeed. I had 'headshake' at Thruxton when I discovered my rear shock had given up any form of damping, whilst negotiating 'Church' at about 140mph flat out in 4th (in the red). The handlebars gave it a good wagging, while the back end was pogoing. Whereas, the 'tankslapper' I had on the 750SRAD, took me onto the wrong side of the road, into on-coming traffic, and was so violent that I could barely keep my hands on the bars. Sheer luck that I had learnt to stay relaxed no matter what, and that I kept the gas on. Would've ended in more than just tears otherwise.

[Jon_W]

A true "tank slapper" is caused by resonance in the front suspension and frame. The motorcycle can be split into systems of springs, masses and dampers. As you ride these are excited by vibrations from the road. At set frequencies these resonate. If you hit the spot on frequency the whole thing resonates as one and you get a full blown tank slapper. Often a bad shake is caused by a frequency of excitation close to resonance, but it dies very quickly as the energy is dissapated.

This is un-recoverable and has resulted in broken hands as well as throwing the rider off....

[jonnydangerous]

never a problem for me....... ;-)
if the wheel isnt on the floor it cant slap........

;-)

[Col]

Have to admit, following from Jon W, that even I have been known to shake with frequency of excitation

Course, back on topic, forgot to mention the most publicised 'wobbly' bike being the Honda ST1300 which has produced the term 'Pan weave' which, apparently, happens 110 mph+ on some earlier versions namely 2002 model. Looked this up and some test discovered a yaw in the rear wheel which caused headshake. In fact some police withdrew its use after a coroners verdict.