F800 GS "Head Shake"

[petecam]

So.....
Recently purchased a lovely F800GS 2012.
It's running Metezler Karoo 3 front and rear.
Hyperpro front springs. (standard length)
Standard rear spring.
Heavy duty tubes with tyre gunk.
Just did a quick trip to France. Above 140KMH (90MPH) the head shake is quite violent.
I have checked the head bearing torque and this is correct.
Tyre pressures are as per the manual. (32 & 36 PSI)
I have done some reading on this and there seems to be conflicting theories with regard to suspension. Some say the forks should be raised up the clamps and the rear pre-load increased adding weight to the front of the bike.
The other theory is the opposite. Push the forks down the clamps and reduce the rear pre-load thus raking out the front forks increasing the wheelbase.
Just wondered what the elders of the internet think (thumbs) or if anyone has had similar issue on a F800GS?
I'm wondering if the tubes and tyre slime are part of the problem? Should I get the front balanced? Or is there an issue with the tyre?
cheers
Pete

[fraserdog]

Sounds like a tyre not suspension issue of some sort to me.

[sledgegreen]

How heavily laden were you on your trip to France? And how was the weight distributed?
Poor loading of luggage can cause this sort of problem. Too much weight high up and far back (e.g.. in a top box) can cause this sort of problem. If the problem has cleared up since you got home (and unloaded the bike), I would be inclined to put it down as a lesson to be remembered next time you go on a long trip on the bike.

[Dave DRZ]

Mine does the same when it goes above 110. Always assumed it was down to tyre choice and rear suspension. To be honest, I've solved it by staying below 110 (thumbs)
Dave

[Helicoptermanr22]

Pete. its the preventative gunk causing this in the front, when the bike was left the gunk would form a sort of wheel weight at the bottom,causing the wheel to bounce up n down. im guessing as it was left for a while.

[Mike54]

Once the slime gets warm it will self balance the tyre, it's not that.
Could be the tyre itself, could be the rear preload is not set correctly. It's unlikely to be the forks (but lets not rule it out yet).
Stick a different front tyre on (a road tyre, preferably) and test it

[petecam]

Thanks all for the comments
To answer the points.
When I went to France I only had a ruck sack no luggage.
I was thinking of swapping the tyre and tube tomorrow just to see what that did.
Currently the forks are set at the default height in the triple clamps (there is a mark about 8 mm down from the top)
The preload is set to near Max which did seem to help however I dont think it the right way to go. Im not a heavy person (78kg) and the manual states the default preload should be set to min.
Rebound is set to default (1.5 turns from max)
I know dual sport tyres are not the best at high speed but this head shake is quite violent. My KTM adventure had TKC80s and that never shook at all, although to be fair it did have a steering damper!
cheers

[Cone]

This may sound daft, but was it windy, do you have big hand guards on. Gusting can make it feel a bit wobbly, my f800 does it sometimes.

[Seminole]

Check the Sag front and rear, body shape can effect weight distribution, if you have a short torso/arms you will load the front more, vice versa for long torso/arms

[Andi_Archer]

Id suggest starting with the basics and rechecking your front wheel balancing and perhaps checking the axle bearings for wear.
If you lean forward on the tank does the wobbling reduce, which would seem to indicate loading issues on the bike?