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High speed front end wobble

F

flipper

Joined Oct 2007
3 Posts | 0+
Aberdeen
Hi all just joined this site as recently got me hands on a 2003 fs650. Luckily enough to have got one that has been tuned by DCR in Preston. Cant believe how mad this thing is I love it. Had a CCM R30 3 years ago and that wasnt a patch on the berg.
Got a problem that hopefully some suggestions might be heading this way.
Bike is for the road only and when I hit approx 75mph the front end starts to wobble, at 80mph its starts to get pretty violent.
I am pretty handy with my tools and have checked everything, forks and wheel are straight, caliper is secure and is ok. New pair of street goldspeeds just fitted.
So ant ideas would be appreciated.
I will keep trawling the forum for any info, no luck yet.
Cheers
JB
 
welcome to UHE flipper

i don't ride SM or street so someone will be along soon to help you i trust.

please try and put your bike and location in your signature. good luck!

regards

Taffy
 
flipper said:
Hi all just joined this site as recently got me hands on a 2003 fs650. Luckily enough to have got one that has been tuned by DCR in Preston. Cant believe how mad this thing is I love it. Had a CCM R30 3 years ago and that wasnt a patch on the berg.
Got a problem that hopefully some suggestions might be heading this way.
Bike is for the road only and when I hit approx 75mph the front end starts to wobble, at 80mph its starts to get pretty violent.
I am pretty handy with my tools and have checked everything, forks and wheel are straight, caliper is secure and is ok. New pair of street goldspeeds just fitted.
So ant ideas would be appreciated.
I will keep trawling the forum for any info, no luck yet.
Cheers
JB
Click to expand...
a worn steering bearing?
On a stand you have a 'dip' while steering
 
RE: Re: High speed front end wobble

Can you accelerate through it? what i mean is when you get up to say 85-90 does the wobble go? if you can go through it ;This may sound odd but i have had to "balance" a motorbike wheel. mark the rim and spin the wheel if it has a tendency to return to the same place then something is acting as a weight {tyre imperfection , something in the tyre like a stray nut etc} If you cannot go through it; it sounds more like a damaged ball bearing or dented bearing race.
 
Re: RE: Re: High speed front end wobble

I had a similar problem with the front wheel on mine recently and after much searching - removed front caliper, replaced front tyre (used same tube), checked steering head etc etc. Finally removed front tyre again and replaced tube - problem solved. I too have found the need to balance the wheel as well.




Scouser said:
Can you accelerate through it? what i mean is when you get up to say 85-90 does the wobble go? if you can go through it ;This may sound odd but i have had to "balance" a motorbike wheel. mark the rim and spin the wheel if it has a tendency to return to the same place then something is acting as a weight {tyre imperfection , something in the tyre like a stray nut etc} If you cannot go through it; it sounds more like a damaged ball bearing or dented bearing race.
Click to expand...
 
RE: Re: RE: Re: High speed front end wobble

In the past I have also felt this high speed wobble on my 05 FS650E around 80mph.

Wind blast on your chest and too firm of a grip on the handlebars can generate minor steering inputs that help enable this high speed wobble. Try to slide your butt more forward or more rearward on the seat to see if this has any effect.

Another item to check is proper rear suspension sag. If the sag is set incorrectly this can have an effect on steering stability at high speeds.

Also check your wheel balance and tire pressures. Different tires/pressures can also have different effects. Generally speaking we run 25psi on our lightweight SM bikes.

A steering stabilizer can mask this wobble but it's only masking the issue.
 
Thanks for all the suggestions, I will check some of them at the weekend if I get time.
Cant drive through it, just keeps on getting worse.
Will be checking wheel balance, setting up suspension for road, check stearing bearings etc.
Will post up how it goes and if I can fix it.
Cheers guys

John
Aberdeen (Bonnie Scotland)
 
Hi flipper.
I experienced the same problem on my enduro before. The speed was lower but anyway.
The problem came when i changed the shockspring. And went away when i got the right springrate in the forks so it matches front and rear.
That COULD be the troll in your bike.
I hop you get it under control.
 
dont know if this is any good to you , but on road bikes particularly the gsxr 600 , it is normally the rear spring too stiff, if the bike dont sink at the rear at speed , it does'nt get the correct geometrical fork rake , making the bike unstable at speed .tank slappers at 140 aint funny when aproaching a bend, but i would have thought the same applies to dirt bikes. the greater the rake angle on the forks (with in reason) the more stable at speed the bike is .
 
i would not be surprised if this is a suspension related issue , also check for correct or even adjustment of the clickers . like rebound adj ... left fork on 2 and right fork on 10 .

when you need 10 & 10 ...yeh 8)
 
one thing not mentioned here is

front tyre pressure
front tyre manufacturer

sometimes a simple change in tyre brand is enough when on the black top.

regards

Taffy
 
Had the same thing with my 2002 650, I reset all the suspension settings to factory settings (previous owner had set every thing he could find on the suspension to max! ) and tightened the triple clamp locknut and now she's runs like she's on rails :D
 
BB

did you get your jets and stuff?

do you still want me to persue it?

regards

Taffy
 
it isn't anything as stupid as the bottom steering head bearing being knackered is it?

I had that happen and it throws the trail out at steady speed and shortens it when you brake........ grreat fun, not!
 
As supertireguy suggests, the most common cause of front end instability on the bergs, particularly 03 and 04 models is incorrect adjustment of the rear suspension. Mostly people don't have the correct sag but on top of that they've got far too much compression and, particularly, rebound damping. Look at your sag, then check your rebound damping on the rear (I bet there's too much on it) and then check the rebound damping on the front. Your suspension, after compression, should return back to normal really quickly.

The next step if there is still some instability for your liking is to lace in a 5" rear rim BEFORE you waste your money on a steering damper.

By all means check your tyres (condition and pressures) but that shouldn't be causing you violent wobbles unless the tyres are totally knackered.

Hope this helps,
Simon
 
If the wheels are true, the odds are that the major problem is due primarily to front and/or rear out of balance wheels/tires.
 
Over tight and worn/notchy steering head bearings will do it, and as Chas says, wheel balance may be a culprit.

I had a GPZ1100 B2 years ago and after changing my first tubeless tyre had to get it balanced. Had a mate with a car workshop that had a device that balanced wheels on cars, so we strapped the bike down on its centrestand and revved up the front wheel with it. The speedo indicated 130 km/h and the front axle was moving back and forwards about 30 mm. Stuck a 1/4 oz lead weight on and all was sweet.

We couldn't believe how much flex was in the forks with such a small imbalance. OTTMH the forks were 37 or 38 mm and the bike weighed about 230 kg.

Worth checking. Certainly balancing the knobbys on my FE650 has smoothed things out a bit and rim locks are heavy.

Steve
 
On the subject of wheel balancing, if you can manage to have your wheels balanced by an electronic machine it makes a huge difference. Most motorcycle tyre shops do it manually which is nowhere near as accurate. I recently had the wheels on my gixxer balanced electronically by my dyno guy and suprisingly noticed a difference at high speeds. Will get the same done to my Berg in the hope of ridding it of the rear end wobble that i get at 140ish that I've only got after replacing the rear tyre.
 
TheSav said:
On the subject of wheel balancing, if you can manage to have your wheels balanced by an electronic machine it makes a huge difference. Most motorcycle tyre shops do it manually which is nowhere near as accurate.
Click to expand...

I have to disagree with you on that one. That electronically balancing is better than manually is better is a myth. As with all things it depends on the operator, not necessarily just the machinery. With a manual balancer you can get extremely accurate balance.

It's also worth keeping in mind that if you walk around the supermoto paddock at european and world levels you'll find the tyre manufacturers all use manual balancers. You'll inevitably find the same thing going on in the British and World Superbike and MotoGP paddocks.

If a tyre is out of balance you can tell by the frequency and amplitude of the vibrations which are normally found at about 65 mph and you can ride through it. Then it can return again at a another speed (multiples of the harmonic).

Cheers,
Simon
 

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