Re: [ST] Skill question on "Tank slap" (Brake Loss)

[pinky <dirac@xxxxxxxxxxx>]

rmasiak wrote:
> Funny you mention this now.  You must have seen the Road America race too.
> 

That would be jamie hacking I believe.

> To add to this question, the racer who experienced the "tank slap" also
> wiped out shortly later in Turn 1.  He explained later that he had brain
> fade and panic because there were no brakes.  Also, I was just reading an
> article, where the author test rode bikes on a track.  He crashed the CBR954
> because he too experienced a "tank slap" then into the next turn had no
> brakes. ??????
> 
> QUESTION:  How does "tank slap" attribute to brake loss???  I've read the
> later posts about what causes this phenomenon, but no body mentioned the
> BRAKE LOSS afterwards.

Depending on the violence of the tank slap, it might cause the pistons 
to back into the caliper a bit.  This would need to be one hell of a 
tankslapper though.  the backed in pistons would make you think that the 
brakes failed, as the first squeeze on the lever doesn't get you the 
feedback you expect.   In a track situation, where you are close to the 
limits, there isn't time to squeeze them again.   thus, you introduce 
yourself to the gravel trap.

>>
>>Just a question on "tank slap", what causes it, how can you prevent it or
>>reduce the chance of it happening and finally has anyone on the list
>>experienced it with an ST Sprint??  If so, was it preventable or could you
>>have handled it better?

you can get almost any sport machine to wiggle under hard acceleration 
(the extreme case being a tankslapper).  The oscillation frequency is 
the harmonic resonance (one of several) in the chassis.   Design 
prevents most of them (as mentioned by andrew).  under hard acceleration 
the front end gets lighter, this reduces the thrust force on the front 
end (via the castor angle).  if the rear end steps out (due to rear tire 
slippage), you can set up a wiggle/tankslapper.

rule 1.  you can't fight the tankslapper, the motor is stronger than you 
are.  My race bike is a little tiny VTR 250, and I have had one coming 
out of 8A at sears point (due to bumpy pavement).  My VTR has around 27 
hp.

rule 2.  don't brake (you will fall down).  try and accelerate through 
it.   get forward on the bike to get more weight on the front end.  when 
the bike gets moving faster (or slower), you will move out of the 
resonance frequency.  The bike *wants* to stay upright and moving 
forward.  let it try to right itself.

rule 3.  purchase new undergarments.

how to avoid most of them.  don't be hamfisted on the throttle.  if you 
see that evil pavement sealant on the road, go easy on the curves, so 
that you don't step the rearend out.

- --chuck
02 st



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