Any ideas on this guys? 091K gixxer stock suspension, forks are flushed, 7mm shim in the rear, Power One V&B, 40mm sag front, 25 mm rear. We are getting massive head shake when powering down the straights at high RPM. It is bad enough we are short shifting to avoid the issue. We cranked up the Ohlins damper to try and compensate until,we can figure this out but it did not help much. I spoke to two different tuners and one said go to 5mm in the rear, the other said to much rear compression and it is Power One issue. Any help to get us moving in the right direction would be appreciated. I want to make one change at a time as avoid the mess of multiple changes at once. Thanks
i think its more of a geometry issue. i think its going to be the issue of the shim in the rear over to much rear compression.
More weight on the front end will help the headshake in a straight line under power, I would either raise the rear with a shim, or drop the front of the bike (more forks sticking out the top of the clamps) like others have said. Both will effect swingarm angle in different directions, which will effect drive grip.
Check steering head bearings, check swing arm bearings, make sure the wheels/tires are balanced and no bent wheels or bad bearings. The steering damper only alleviates the symptom, doesn't correct it.
? You've just made the thing twitchier. Steeper rake, less trail. Try lowering the entire bike, front and rear, equally, this will stabilize it.
OP said on the gas 'powering' down the straight, he is getting headshake, to me that would unweight the front (giving the bike more trail) and as a result he is getting headshake. But hey, I am new a this motorbike thing so who knows, go with what Rick says :up:
My R1 settled down after I softened the rear spring up a bit. Much better now. Was too stiff by 60 lbs. Must have been acting like a pivot, instead of squatting a bit.
FWIW..... I would try steepening up as well, also if you don't have one get a bum pad to push the rider forward. I don't have the suspension or tyres you have so this may not be that relevant but I have 15mm fork through the clamps with 30mm Ohlins, TTX rear with no shim but ride height raised a few turns (cant say exactly the shock length without taking it out) and N-Tec slicks. Smooth as up to 175, haven't been (much) past that
1/2 way down the straight when under power in upper RPM's. Short shifting solves the problem but is costing time. Bike is great throughout the entire corner, no issues. The only issue so far is the head shake on the straights.
if the bike is finishing turns really well, i'd back of 1 click on rebound on forks and add 1mm of rear preload to the spring.... seems to be as the bike picks up in power the front isnt really staying in contact with the ground firmly enough. cheers.joe.
This is what Dave Moss did to my ZX6 with the same issue. I also lowered the clip ons a bit. Seems to have helped.
