head shake - this is new...

[VladTepes]

Well it's either new or I've only just noticed it.

When riding at say 30kph + if I let go of the bars the head starts shaking. It's disconcerting and I think if I left it for long enough it'd develop into a decent tank slapper - so obviously I don't let that happen. 

Tyres
Rear - worn in the middle but plenty left on the sides. It's not a square profile or anything extreme like that yet. But pick the commuter. 
Front - somewhat worn esp on RHS of centre (as appears typical)

Any idea where to start at trying to diagnose the cause here?

[Horse]

I would start with the head stem bearings , barring tyre issues it will be something loose in the frame/ suspension ie axles , swingarm pivot but every time I have experienced this it has been the head stem bearing play . If all of that is not an issue the tyre could be suspect but it has not been my experience

[gsxbarmy]

First try the same trip - but without your topbox (if you have one on) as this can cause a headshake under certain conditions (as the top box sits quite a way back off the rear tear, as opposed to more over the rear tyre).

If it stops doing it - then the topbox is the cause and is a known issue - no way around it.

If it carries on doing it - check rear wheel alignment and tyre pressures. Also (and this may sound strange) check your chain adjustment.

[VladTepes]

@horse - any easy way to to check the head stem bearings?

@gsxbarmy Hmm I did change the topbox recently to a slightly larger one.
I'd have never thought of that - will give it a go.

As for chain adjustment - it's gone from well adjusted to pretty loose in just 3 weeks, thus my other thread re chains and sprockets.

Wheel alignment - I'm hopeless at that, I must admit but it seems pretty damn close.

Tyres - tyre pressures seem to be OK / what I usually run.

[Hooli]

My topbox always caused exactly that until I had to bolt the box on, now it doesn't move the steering doesn't shake.

I'd go for tyre wear from how you describe the front one.

If you hold the front brake on and rock the bike back n forth, any clunk or movement in the stem is too much. I tend to lean the bike slightly on my hip and check with my left hand's fingers just touching the stem and top of the frame in front of the tank. You'll notice smaller amounts of play that way.

[Kiwifruit]

Tyres for me, l'd be checking for an abnormality. If you spin the wheels by hand you may feel a small bump. Sounds like the tyres might be nearly done.

[Grumpy old man]

I would bet on it being the front tyre 

Michelins did this on my Tiger Sport when 1/2 worn Metzeler and Pirelli no problems even when almost thread bare
MY ZX 14 did that on new Mich road 4's

I always change a set even if 1 still has good tread

[KiwiCol]

You wanted Road 5's anyway Mike . .  now's your chance.

[grog]

Agree with tyres, they are worn so need replacing even if no shake. Head bearing adjust, also something to do. If you adjust you then know correct. Thats my thoughts.

[Horse]

@horse - any easy way to to check the head stem bearings?

@gsxbarmy Hmm I did change the topbox recently to a slightly larger one.
I'd have never thought of that - will give it a go.

As for chain adjustment - it's gone from well adjusted to pretty loose in just 3 weeks, thus my other thread re chains and sprockets.

Wheel alignment - I'm hopeless at that, I must admit but it seems pretty damn close.

Tyres - tyre pressures seem to be OK / what I usually run.

As has been said one way is to rock on the front brake on feel if there is any play or get the front wheel in the air and grab both fork lowers and rock back and forward also checks free play but as per the manual there should be from memory 300-400 grams of preload on the head stem at the handgrip With the wheel off the ground.

[Hooli]

get the front wheel in the air and grab both fork lowers and rock back and forward

That is also a good way to spot play in the fork bushes, as you can feel/hear where the movement is easier than from above.

[DP1400]

I`d stay with the front end and check the easy stuff first, ie. head/wheel bearings, but its worth considering whether you have a brake defect developing - a very slightly warped disc binding on the pads maybe? I had this problem on a `Blade once, the slower I rode amplified the feedback through the bars. Easiest resolution was to keep the front wheel airborne..... Sorry, couldn`t resist the last bit!!

[VladTepes]

Brake discs replaced not too long ago. Doubt its that.

You wanted Road 5's anyway Mike . .  now's your chance.

True But I've gone off the idea of Road5's (only because I've always had Michies and want to try something different) so the Bridgestones which come recommended on here  a lot are a good chance.

[mlivkovich]

Maybe tire cupping makes front end shake at low speed

[Eric GSX1400K3]

Vlad,

Have you checked that your bar ends are still fitted tight? I lost one somewhere , did not notice it until i took my hands off the bars and the bike started to want to go left.  I ordered new ones that night, heaviest i could find, as i run aftermarket Eaton tapered bars which are lower and wider.  Makes the steering nice and light.  Worth a check i think.