Speed Vibration

[Uber Dave]

*Speeds attained at work on private land.... ah the joy of playing on airfields!*

This is difficult to explain, but I will start off by saying I recently had a new tyre fitted to the front.

Basically when I reach 100mph the bike starts to very very lightly shimmy about under me, at exactly 105mph the shimmy turns into a vibration which I can initially feel under my feet in the foot pegs. Get to around the 110 region and the vibration gets stronger still and I can feel it through my seat. Around the 120mph mark it gets quite violent and I have to back off the throttle because it quite honestly scares me a bit!

The reason I am asking is that I have shed a front wheel balancing weight before on my previous bike and all the vibration was through the yoke and bars not the main part of the bike as I have explained hence why I am not sure if its the front or something else which may be causing it.
The only time before that I rode it at any speed was at work about a week before the tyre change and I hit 158 without it vibrating at all, other than the odd bit of wind moving me around but definitely not any vibration like this so something is wrong without a doubt.

I am looking at doing a track day in a month and a bit so this needs sorting really!

Any Ideas?

[spudgun]

get both the wheels re balanced, if it makes no difference you can rule it out

do you have a steering damper?

bar ends still fitted?

[Uber Dave]

No Steering Damper and the bar ends are indeed still fitted.

Meant to say in the original post, there is NO vibration in the bars at all or that seems to come from the front end it is entirely from the pegs seat and gives the impression that its the back of the bike which is the problem. Could an out of balance front tyre do that?

[Jon_W]

I'd check a few things.

Rear wheel balance
Rear wheel roundness
Chain tight spots
Rear sprocket
Distorted rear brake
Head stock bearings
Axles are tight
Wheel alignment

[Scotty]

Dave, if the tyre's the only thing that's changed recently then it's likely to be the source of the problem - first thing is to check the balance, just because whomever fitted the tyre "balanced" it doesn't necessarily mean they did a proper job of it (working for Phase One in the past I've had to re-balance wheels with tyres freshly fitted and balanced by the Dunlop crew before we could consider using them). Whilst checking the balance, spin the wheel and check for run-out; an egg-shaped tyre or possibly a bent rim could cause your problem. Let us know how you get on...

[jonnydangerous]

yup, agree with Scotty....id check the front balance....also, the new balance weights may not have stuck, or been knocked off and would cause the problem.

also front "sticky" bearings dont give a true picture when balancing the wheel, so check they arnt a bit "notchy" (or compressed too tight onto the spacer between the bearings) it may have balanced up fine when the tyre was fitted, but a tight spot on the bearing may mean that extra weight was added when it wasnt needed, this would LOOK like the wheel was balanced but it wont be balanced at bike speeds.....

check the back also if the shake is still there after the front is balanced, as a weight may have come off the rear wheel.....(im sure weve all spent ages chased a "Coincidence" fault before)......just in case!!!

[silly_simon]

Also I would check the front wheel axle nut hasn't been done up too tight [smiley=thumbsup.gif]
Also check the tyre has been seated on the rim correctly

I have had it in the past where some tyre centre's seem to think that the axle nut should be done up as tight as they can get em >
Bloody gorilla's :-/

[Mark_Able]

Pretty much guaranteed to be wheel balancing. Either they've cocked up the front, or you've lost one off the rear. Name and shame, who did the fitting? I'll tell you now, I will NEVER use Protyre in Westbury as long as I live. Had a puncture that could not be repaired. Stopped in with my students at 9.30am to get a new tyre fitted. Wouldn't sell me one tyre as they didn't have my make, and wouldn't mismatch tyres (never been a problem in the past when I've done it). Had to buy two. Took them until 12.00pm to fit two tyres! I'm seriously pissed off now cos my pupils are losing valuable training time which I will have to make up at the end of the day. Fitter says I should just run it up the road to make sure everything is right! I'm thinking 'surely you should know if everything is ok'. Anyway, I trickle out of the place (knowing to be careful on new rubber) and nearly highside myself. The bike's squirming all over the shop, get as far as the Ham, turn around and go back. Something is seriously wrong. Turns out to have 22psi in the front, and 15psi in the rear! Complete muppets. Tyre pressures sorted, make sharp exit. Over the next few days it becomes apparent they haven't balanced them correctly, as I suffer similar problems of being shaken out my seat when I do any kind of speed. Take to Phoenix Motorcycles, have tyres refitted and balanced, no problems after. Moral:- Stick with decent bike shops that know what they're doing. >

[Uber Dave]

As for who fitted the tyre its irrelivant as the place is in Yorkshire.

I also have the bike booked in for its 6000mile service on Wednesday at a Yamaha Main Dealers Servicing Dept and am getting them to re-check the front end. Part of the service includes stipping and servicing the brake calipers anyway so it wont be much more work to whip the wheel out and check it.

Will keep you all informed!

[Uber Dave]

Well problem is now solved. Was the front wheel which was out of balance. I have also since found out that the tyre change was just that and that didn't include balancing so its partly my fault for not checking.

Still the tyre & fitting was cheap and and balance was done as part of the service so it was free as the wheel was out anyway.

Bike is now back to normal and no longer vibrates which s good as there is a chance of a track day coming up