You’re right Anito, pushing harder on the bars actually feeds energy into the headshake/tankslapper causing it to get worse in some instances.
There’s two ways to approach this problem.
The first is to increase the weight on the front wheel in order to increase the forces trying to straighten out the wheel after the tankslapper starts. You can also increase these forces by increasing the trail dimension by using the street fork angle setting if your bike has this adjustment. Shifting your bodyweight forward will load the bars downward to reduce the tendency for the headshake to start, and to keep going once started. Of course, this is hard to do when you’re accelerating out of a corner so that’s the time when headshake is most likely to begin.
The second approach is to increase damping with an adjustable Ohlins unit. Damping forces are velocity dependent, so the higher the velocity the higher the damping force opposing it. Consequently, when you crank-up the damper to damp out headshake (a high velocity oscillation, called wobble) you also reduce the bike’s ability to transition into corners (a low velocity movement of the bars) and more important, you increase the tendency of the bike to weave from side to side at high speeds.
For those of you who haven’t experienced this phenomena, see one here:
http://www.randtclub.com/Video/cedwa...pper_tt99.mpeg As you increase steering damping you gain increased control over steering oscillations that are set up by uneven road surfaces and even side wind gusts. As the side-to-side speed of the steering increases, so does the damping effect. This results in a smooth easy-handling ride at low speeds combined with heavier dampening during extreme situations The trade-off between handling feel and steering stability is a personal choice.
When collecting information for our Ducati Suspension and Setup Guide I came across these informative tidbits:
Tankslappers A tankslapper is a potentially dangerous phenomenon that has been haunting motorcyclists for decades. It’s called a tankslapper because the handlebars suddenly seem intent on battering the fuel tank into submission as the front wheel thrashes from side to side .
There are two linked forms of motorcycle instability: Wobble, which occurs at low speed and causes the front wheel to rapidly flip back and forth like that of an unruly shopping trolley; and weave, the fish-tailing effect that happens at high speed
An outside influence is needed to spark these phenomena. Subtle undulations accidentally introduced into a road surface during its construction can be enough. These need be no more than a centimetre in height and stretch over just a few metres, so long as they have precisely the right wavelength between peaks to "tune in" to the wobble or weave dynamics of the bike and its rider - values determined by intrinsic mechanical properties.
Other factors need to be present too. The bike has to be travelling at just the right speed. It must also be taking a corner, with the bike leaning at a particular angle. Together, these elements enable the vertical oscillations caused by the bumps in the road to become amplified and transmitted to the bike’s steering - like a tuning fork applied to a guitar string. The magic combination sets loose the unseen forces behind the tankslapper.
Engineers have experimented with ways to reduce the extent of the problem. For example, they have found that heavier riders are less susceptible to the problem than lighter ones. The amount of weight on the front wheel is important, so tankslappers often occur when exiting corners under power when weight transfer off the front wheel occurs. (Ref 5.)
Steering Damping The stock steering damper is not adjustable but provides a fair amount of damping that is suitable for most road and track applications.
Supplied on some models, the Ohlins Steering Damper adjustment knob has 16 different damping positions. The recommended setting is the midpoint 6-8 clicks from full soft. Full hard is 18 clicks clockwise from full soft.
Track surfaces are smoother than typical roads, so less damping is needed. The steeper steering head angle is less stable (less self-correcting) so more damping should be considered.
As you increase steering damping you gain increased control over steering oscillations that are set up by uneven road surfaces and even side wind gusts. As the side-to-side speed of the steering increases, so does the damping effect. This results in a smooth easy-handling ride at low speeds combined with heavier dampening during extreme situations The trade-off between handling feel and steering stability is a personal choice.
By its very nature a steering damper will spoil your bike’s steering a little. It’s main value is to provide protection against tankslappers (a severe case of an instability called wobble.) A tankslapper is a rapid side-to-side motion of the handlebars caused by a combination of whacking the throttle open exiting a turn, thereby reducing the weight on the front wheel, and encountering bumps that start the steering oscillations (that often grow violent, especially at high speeds.) (Ref 4.)
References:
(4.) Road Racers web site
http://www.roadracers.co.uk/dampers.htm (5.) Farrar, Steve, Avoiding Tankslappers