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Discussion Starter · #1 ·
what causes this? why are litre bikes more prone to this if at all? how do you correct this if it happens while riding? my r6 used to do it when i first got it if i was accelerating really hard of coming out of a turn really hard and bringing the front end up. when i made my suspension stiffer it almost completely eliminated it?
 

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Liter bikes aren't more prone to it, it's a side effect of an aggressive chassis geometry, rake and trail. If they quicken the steering by reducing the rake then instability is increased... It's no worse than a 600 but it's excaserbated(sp?) by the high power of the liter bikes.

Bikes like the CBRXX have the power of a liter bike but don't suffer the same problems because the rake is rather conservative.

No your R6 never did it or you'd be picking your ass up off the pavement or have some sort of horror story about it. What you experienced is headshake and EVERY modern day sportbike suffers this... A tankslapper is the worst thing in motorcycling, that and a highside.
 

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I recently high sided at 100+,,,, can you say TANK SLAPPERS while leaned over... OOOOPS /images/icons/smile.gif Surgery sucks. /images/icons/mad.gif

 

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Discussion Starter · #6 ·
doesn't headshake turn into a tank slapper if not corrected? i have never gone into a full tank slapper(lock to lock) but have experianced headshake.i thought headshake was more of a strong vibration or figidy(sp?) over bumps? do steering dampners eliminate this completely? once a tank slapper happens(lock to lock) can u fix it?
 

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Headshake is nothing, to be honest if headshake bothers you you are in the wrong hobby. Headshake is just when the wheel gets light and shakes a bit, usually when you are full throttle and at the top of the rev range in the lower gears.

Tankslapper is a violent episode, where your whole bike shakes like you've never seen, your bars go from lock to lock repeatedly to the point most people can't hold on anymore, the oscillations usually go through the rider into the rear of the bike and you are all done at that point.

I have a video at home of a guy that was racing at the TT and got one bad... Of course nothing worse than the one my friend had right in front of me one night.

There is also another one around recently of a Gixxer1000 after a long 3-4th gear wheelie, he doesn't have a full blown one but it's enough to dirty your underwear, and that's with a damper.
 

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Discussion Starter · #10 ·
imagine going around a corner and your rear starts to slide out and then grabs and now tilts the bike in the other direction(you were leaned over left. now pivot on the wheels so the bike is now leaned right) but in this processs u no longer are holding on because it is so violent and get thrown in to the air! a low side is when u turn and loose traction typically with the front i believe and just slide out. so u see what i am saying. if you fall to the side you are turning to u are already low to the ground ! where as if you start to lowside and get grip then get launched the other direction u high side. make sense?
 

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Discussion Starter · #11 ·
ian all i ve had then is headshake, thats not a major concern. i saw the vid of the black gixxer(i think) tha looses it and crashes under the bridge. that was sick
 

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I think that is the Isle of Man crash I was talking about, but it wasn't a Gixxer I don't think, it was a while ago. That is exactly what a tankslapper is.
 

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<blockquote><font size=1>In reply to:</font><hr>

do steering dampners eliminate this completely? once a tank slapper happens(lock to lock) can u fix it?


<hr></blockquote>


Not necessarily but I believe it depends on how you have the damper set up. I have one on my 748 (stock damper) and I still get a headshake from time to time when I come across surface irregularities or poor road/bridge transitions under throttle. They are short lived and over before you even have time to think about correcting it.

To transition a headshake into a tank slapper I'm guessing you'd have to what...be on some really crappy asphalt (bumpy) and roll off the throttle to get more weight on the front quickly and let things go from there?

When in doubt give it gas.

 
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For those who haven't experienced it or don't know the terms... I did some looking online for well written deffinitions.

A violent oscillation of the front steering. All steering systems on motorcycles have a natural frequency (or speed) where, given an initiating disturbance, they will tend to oscillate quickly from side to side, each oscillation bigger than the previous. At its worst, the steering will be hitting the stops very rapidly?thus the term ?tank slapper.? Damping prevents this from happening, by the rider?s arms and sometimes helped by a hydraulic steering damper. The newer sport bikes with their steeper steering geometry are more susceptible.

The most common scenario is to be accelerating rapidly from a corner over broken pavement where the front wheel is barely touching the ground. A combination of bumps in the pavement and the rider attempting to steer the bike while the front wheel is slightly off the ground can cause an initial disturbance that is exactly at the natural oscillating frequency of the steering and overwhelm whatever damping the rider or bike is providing. Most people, however, seem to be able to ride them out. Of course, worn steering bearings, worn tires, accident misalignment, poor suspension setup, etc. can all make the bike more susceptible to this problem.


I think the Twist of the Wrist II book had a great explaination in it with pictures to describe the physics of it and everything... maybe I'll remember to bring it in tomorrow and scan it in for ya.

Here's another good vid of a tankslapper seen from the spectator's view-point and shown in slow motion. http://www.rsvs-furman.si/Video/Moto/tt99.mpeg

 

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YZROOSTINYA, like IanR1 said, the bike geometry has alot to do with it. The reason an R1 SEEMS more prone to it is how fast it's front end lightens up on accel. What causes it on accel is the front tire leaves the ground slightly and the back tire begins to accelerate faster than the front tire and as the front tire just scrapes the ground it has to accelerate VERY fast to keep up. Each time it scrapes it leaves the ground again slightly. The sudden accelerations it what causes the headshake. That's why most tankslappers happen on decel. The front tire isn't up to speed when you get out of the throttle and when it comes down and it's not up to speed the headshake can become violent and without the right corrections it quickly can become a tankslapper. If you don't correct before it goes lock to lock, there aren't too many riders who can recover.



If you want to know how good the tail section of an R1 looks...Just ask a Honda rider!/images/icons/cool.gif
 
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