I think you missed the entire boat!
The thread title is "What caused the tank slapper"! The wheelie landing created the head shake. From there it developed into a monster slapper. What made the bike go from head shake to slapper? If you have ideas, I'm happy to listen and learn?
I think we all know landing a wheelie with the tire off center will create head shake. Help us out on how to avoid the slapper once we have headshake. We have two good examples of bikes with headshake. One bike settle down and the other was quickly out of control. What made the difference in these two bikes? How would your bike act in a similar situation?
That was a very nice and almost to the point response, and I appreciate it. Yes, I have ideas, but I am not trying to "teach" anyone with my "absolute knowldege" which is rather limited, but I am always in a quest to better understand things. Just trying to sort things out in a logical way.
A. Let me make a statement about the objective of suspension which I think we all should agree with no issues -
this is to have traction at all times.
B. Let me make a general statement about the objective of fixing the misaligned front wheel (I am purposefully avoiding calling it a headshake or a tankslapper to avoid ambiguity) -
this is to have a straightening force of just enough magnitude (let's call it the S-force which is the result of rake and trail) applied to the front wheel so that the front gets aligned. Notice that too big S-force creates such a strong turning momentum for the steering that the front does not stop at the point when it is straight - it's the opposite - at this point, it has the maximum turing speed.
C. When the bike settles down with the front misaligned and the front tire regains traction, the S-force attempts to bring the wheel into an alignment. Let's freeze this point in time and analyze it. If there was no traction at all (for the sake of argument), the S-force would not exist, and on the other hand, the better the traction at this point, the stronger the S-force will be. So, the logical conclusion is that the better suspension you have the greater the S-force will be. And it's feasable to think that the S-force maybe too powerful because of the good suspension. What can reduce the S-force at this point to a more reasonable level? It's the steering damper.
D. OK. Thanks to the S-force, the front wheel was given a turning momentum and it now passes the point of alignment (i.e. when the front wheel is almost straight). According to ideal scenario from item B, it would be nice that the S-force is only strong enough to bring the front straight. Unfortunately, a better suspension would provide a too strong S-force. Thus, a good suspension plays a negative role at this point of time.
E. Now, what can possibly counter act this turning momentum of the front steering, exactly at the point when we need it most - when the front is aligned? Since the wheel is almost straight, no matter what traction the front wheel has (i.e. good or bad suspension), the S-force at this point is almost zero. Well, the answer is almost obvious - the steering damper is the only force trying to keep the front straight.
F. Because of the turning momentum created by the S-force in item D, the steering and the front wheel start swinging away from the aligned position. Let's see what forces try to stop the steering from swinging into a more misaligned position. A good suspension will provide better traction, thus making the S-force (now acting in the opposite direction) to slow down the swing to the other side. Here, a good suspension plays a positive role. Another force which tries to slow down the swing is the steering damper. Unfortunately, even the positive role of the S-force here is reduced by the fact that the S-force is initially zero when the front is straight (and when we want the S-force to be big) and grows as the wheel is more and more misaligned.
G. Such swings of the front wheel - side to side - will only subside when each consequtive swing is reduced at least by a little bit compared to the previous one. There are only two forces involved in this process - traction related S-force, and the force provied by steering damper. The S-force plays a negative role half the time, and the positive role another half the time. A better suspension only increases the S-force. While the steering damper force always works to our advantage.
So, I can only conclude that if a headshake developed, I would not want to rely on my suspension only, but also on a steering damper.
Now, I have to make an important point about a good suspension during normal riding. Since a good suspension would provide a better traction cornering over bumps, when the front is light on strong acceleration out of a turn, etc., a bike with a good suspension will not even go into a headshake where as a bike with poor suspension will. The reasoning is simple - the moment a bike with poor suspension loses traction for just a moment, the steering input from the rider (which is alway present in a turn - although very light), immediately misaligns the front wheel, and when the next moment the traction comes back we got the S-force working again.
During normal riding where the initial misalignment of the front wheel is not excessive, it would seem that a good suspension would prevent a headshake from happening altogether, or if it does happen, the S-forces will bring the front into the alignment.
However, when landing a wheelie, the misalignment of the front wheel combined with hard landing produce the initial S-force of such magnitude that the front wheel swings to the other side even further which in turn creates even more powerful S-force in the opposite direction ultimately causing a tankslapper.
So, it seems both a good suspension and a tight enough steering damper play a role in overall stability. But it seems that a steering damper is more important for landing wheelies.
I think I tried to conduct a logical analysis. I need another bloody merry...
)
Sorry SteveO... had to say it..
lease:
:stoopid: 
Just like every knee down turns into a highside!
