The Place

Newbie Driver and passenger, some guidance required please.
We have been to three sessions at Teesside, each time we have varying degrees of head shake when coming off the throttle and getting ready for the corners, left or right handers. Some laps its not evident, other laps it is. Obviously affecting my confidence to try and go faster. Steering damper is on the stiffest setting, this helped slightly, tyre pressures checked double checked and even adjusted without making a noticeable difference. Front suspension is Koni units, initially on middle setting, have tried on hardest setting, problem still existed. Not yet looked at rear suspension setting, single Maxton unit. How much adjustment to make on the rear? Steers in a straight line, steering head bearings have no play, very slight play in the rose bearing on the brake caliper holding plates on the front. All wheel bearings and swing arm are ok.
Chassis is a Shelbourne circa mid 90's I think, with pc25 Honda motor.

Any ideas? or is it down to driver/passenger not working properly?

If it's some laps not others then you're not far off on setup. Is it on part closed throttle or full off?
Have you spoken to the previous owner? They might be worth a call see if they had trouble, like are you running the same tyres or very different in weight?

What pressure are you running in the front?

I agree with Steve, if it doesn't happen all the time then I wouldn't have thought it was set up. Do a few trial corners, get your passenger to move before you brake & then get him to move under braking, obviously going a bit slower & see if there is a difference.

Steve,
Its on full throttle off, have spoken with last owner and he did not have this issue. We are(or I am as the driver a lot heavier than the previous owner) tyres are same as when it changed hands, pressures are 12 front, 14 back and 20 in the sidecar wheel and are Avons. Shaking is quite obvious to the bystanders at Teesside on Tuesday. Tried a different passenger but laps got cut short due to oil on track, still shaking a little with a different passenger. Will have to get my passenger to try different technique......lots of learning for both of us. Thanks

Have the wheels been balanced recently? Even if the wheel weights are still on there they might have just been stuck back on or not re-balanced when tires were changed. Might be worth checking.....

We run 14 front and back in our Avons,12 seems a bit low,especially at this time of year with the cold ambient temprature.Are you braking when it shakes its head?

Is it happening on application of the brakes or just on rolling the throttle?

tried 14, front and back. Happens when rolling off the throttle before applying the brakes.

See below.

How old are the tyres ? Could it be cold tyres , ie not getting temp into them. Does it get better as things warm up ? Can you adjust the trail on your bike?

you have to much trail if its not ajustable get some one to make so joe heys

I think Geoff has the answer put a new tyre on the front or wait for the weather to warm up so you can get heat into the tyre, if you are out on a cold track try putting a wet on the front and see if it does it then. If all else fails give it a little more trail as Joe says. It can also be that as a new team you are not aggressive enough turning in so you are not getting heat into the tyre - this can be difficult to overcome as the wobble makes you want to go slower! a good practice is to be hard on the throttle or hard on the brakes so get used to not "trailing" going into corners.

Hi Gerald, in your original post you say it shakes on some laps but not on others?
If the problem was a setup problem then you would have the shake all the time not intermittent.
I still agree with steve that you are not far off a good set up, don't go changing a host of things, that could make it worse.
Stay with the settings you have & try to adjust things slowly. I'd still look at the movement of the passenger.

Hello Gerald,I have had this problem with several bikes so we decided to put them on our jig and we found that the steering head was laying over. And the shaking was only on closed throttle and not braking, immediately they were applied the shaking stopped.I think the reason is when you shut the throttle before you brake you put only a light load on the tyre and it has heavier contact on one side, I believe this causes the wobble and when the brakes are applied the problem stops because the tyre is in better contact with the road and is not kicking on that side of the tyre. And as Joe Hays has said too much trail will make this worse. I hope that this explanations useful.