Originally Posted by FuTAnT
You've got to remember that head shake is a component of various elements.
Steering angle, front wheel weight and suspension set up. If it's quite steep it will want to slap. I dare say this has to to with the natural damping effects of the steering angle. You've also got the front wheel weight. The more weight that is over the front wheel there is less tendancy to shake. It's either weight on, or completely off so the road doesn't contact the wheel. Lastly you've got your suspension. You need to return the tyre to the road as quick as possible so it's not floating about and able to move in mid air. This is why the stock suspension is so ****. It's way overdamped and undersprung at the front. The result is it hits a bump and doesn't move then slaps like a bitch.
Essentially it's that middle ground where there is little weight on the front wheel that causes all the trouble. Ie under hard acceleration, or when you hit a bump mid corner and the suspension doesn't return the front tyre to the ground in the correct manner.
Hence the comment that tank slapper can be sorted through suspension (and they can, as my bike is fine now).
You really should take a look at Tony Foales' books. He has proven empirically that steering angle has nothing to do with instability, rather trail is the single most important geometrical aspect that affects a 2 wheeled vehicle's straight line (on smooth or bumpy surfaces) stability. Wheel weight and suspension all can contribute to the relative stability, but small trail figures = headshake and potential uncontrolled lock to lock fork movement.
While total trail is also affected by the rear wheel (ie: swingarm length and relative distances between axle/swingarm pivot etc.), it is the trail (or lack thereof) in the front steering mechanism that determines a bike's overall high speed stability. Simply optimizing your suspension does not change the geometry as the 929 (and to a slightly lesser degree the 954) have very small trail numbers with respect to wheelbase. Add extremely large static and loaded front wheel sag (in a stock configuration) and you further reduce this trail figure making the "as delivered" package a handful under the best of circumstances.
Many Blade owners get some very suspect advice and proceed to "fix" their bike by lowering the triple clamps in an attempt to make an already quick steering bike turn even quicker.
As I have mentioned before, lowering the front end (or conversely raising the rear) do not put "more weight" (well, it actually does, but such a tiny amount, that any positive effect is negligable) on the front wheel making it turn faster. It does exactly 3 things:
Reduces ground clearance
Reduces trail and increases high speed instability
Makes turning the bike require less effort from the rider
Actually, raising the rear doesn't reduce ground clearance and although it makes turning easier, it can also (depending on how far it is raised) reduce traction during corner exit and increase oversteer under acceleration.