Low speed head shake

Morning, wondering if the Org can give me some guidance.

I was riding over to Oxford yesterday and at one point I was slowing under engine braking for a roundabout whilst having light pressure on the bars to resty wrists when the bard began to shake quite badly.

Putting pressure back on the bars stopped it, but I could feel the vibrations. It seems to happen, of at least can be replicated, under engine braking everytime. I can't decide if it's when it reaches a lowish RPM (2000-3000) or a lowish road speed (20-30).

I've tried a quick shake of the front end as best I could in my little sisters back garden, but nothing. I'll have to look closer when I get home but that's going Oxford to Stoke.

Any suggestions where to focus my attention first? Is it likely to be wear or I'd it normal? If it's been doing it a while, it could explain why my wrists hurt after riding

cheers

[rictus01]

bit vague, but head bearings either loose or shot, lost a wheel weight, tyre pressure? start with the cheapest and go from there.

Cheers Mark.

The shake is like grabbing the bars and wobbling them left to right quckly. It's a short movement but quite fierce. Not uncontrollable but worrying.

No wheel weights to go missing, I'll check pressure before I set off and the rest when I get back

[Spanner Man]

Good morning.


As Rictus says check the obvious first. Many such instances of 'head shaking' come from an issue at the rear of the bike. So also check your suspension linkages, rear shock absorber, rear wheel bearings, & so on.


Cheers.

Originally Posted by Spanner Man

Good morning.


As Rictus says check the obvious first. Many such instances of 'head shaking' come from an issue at the rear of the bike. So also check your suspension linkages, rear shock absorber, rear wheel bearings, & so on.


Cheers.

may sound daft but was the surface pitted hatched box paint markings? if so if your tyres are squared off could be them tracking inperfections!

I will have a good look over the weekend. I'd hope it's not linkages etc at the back as that was all stripped and regreased when it had a replacement swibgarm a few months ago. Could it be that I had all the luggage on? Top box and 2 panniers then? I'll try later with no luggage.

Seems to do it on all road surfaces.

Tyres aren't that squared and it was upright in a straight line

Originally Posted by 7755matt

Could it be that I had all the luggage on? Top box and 2 panniers then? I'll try later with no luggage.

yes...

redistribution of weight over the rear wheel pushes the back down and can "lift" the front causing a shake..

[embee]

The front forks are a castor, and just like those supermarket trollies if the various parameters are right (or rather wrong) then it can shimmy. The frequency depends on the stiffnesses and effective mass or inertia, so there tends to be a quite closely defined speed range when it will be provoked.

As the others have said, check the obvious first, and having luggage hung out the back increases the effective inertia considerably so lowers the speed at which it will occur. Tyre pressures directly affect the stiffness, and steering head bearings are a critical element of the system.

The tricky one to deal with is if the tyre carcass stiffness is inappropriate for the bike. This used to be quite a common problem with high profile tyres on older (wobbly) bikes, but modern frames/forks/tyres suffer much less usually.

If you've only just noticed it with the luggage fitted, then that'll be prime suspect.

[ixlr8]

Originally Posted by rictus01

bit vague, but head bearings either loose or shot, lost a wheel weight, tyre pressure? start with the cheapest and go from there.

Cheers Mark.

or worn front tyre?

[Bibio]

i would look at the shocky. mabee a loose top/bottom bolt. i had the exact same feeling and it ended up that it was 2 things.

1. the bottom bolt was rubbing on the dogbone.
2. the compression was to soft.

ok so i had fitted a gsxr shocky, but what you are describing is exactly the same problem i had. it also materialised at about 80mph as well as low speed.