Front Suspension Wobble on Highway

[a3dudek]

Hello all, my first post on the site. i have a 1980 xs1100 special with the air dampening front forks. i took it out for my first ride and found that the front shock was fine up to about 70 MPH. when i hit about 70 MPH the front shock began to go up and down very rapidly and cause front end shake/vibrations. i have fresh oil in the forks and have the pressure at 15psi. i was wondering what could fix this and how much air people are running in there forks. i saw that the max psi is 32. i was going to increase the pressure but wanted to know if there was anything else i could do, or if anybody else have experienced this.

Thanks
adam

[BA80]

Is your front tire balanced?

[CatatonicBug]

I had exactly the same issue, at about that same speed too. The tire was balanced, but it was actually out of round by just a tiny amount. Raise the front end off the ground and site over the surface of the tire, looking at some fixed point. Spin the tire and see if the surface of the tire goes up and down while spinning. When I took my tire back in to where I got it, they replaced it for free.

[a3dudek]

thanks for the help, i am not sure if the tire is balanced because i just got the bike but i will check asap. i will also see if the rim/tire isnt perfectly round.

Thanks guys!

[GLoweVA]

My 80G does that too at about 75. My front tire is getting close to needing replacement, so I'm assuming that mine is a tire issue and not a suspension issue. (but I do have a leaking fork seal, and some of the fork oil has leaked out, so that might be a factor too)

[BA80]

I have 4 different front wheels for my SG and 3 of the 4 are fine but there is one that appears to have no problems but it does that bouncy thing with whatever tire I put on it or how much balancing I do just between 70 and 75.

Not sure why.

[a3dudek]

i have full fluid and the fork seals are not leaking, has anybody tried to crank the air pressure up?

BA80 - does it go away once you go over 75mph?

[BA80]

BA80 - does it go away once you go over 75mph?

Yup........and it's irritating when I'm on a long trip because that's right where I need to run sometimes.

[motoman]

i have full fluid and the fork seals are not leaking, has anybody tried to crank the air pressure up?

Never a reason to air those forks over 15psi. I run 6-9psi just to force lip seal tighter against fork piston. Anything much over 36psi, and U won't have to worry bout seal removal......the air pressure will take care of it for U.

[a3dudek]

yeah i am running 15psi right now, i read 36 psi was the max and had no intention of going over that or even over 20 psi for that matter. didnt think that would rally help anyway...

[a3dudek]

do you guys think an over inflated front tire could add to the problem?

[CatatonicBug]

do you guys think an over inflated front tire could add to the problem?

Possibly, but only if there are other issues already. Adjust to 40-44psi, and ride, and see if the problem persists. I bet it does.

[Poprock]

Fork air pressure over about 10 causes "stiction" of the seal/fork leg. I had mine at 22# for a while. Front stiffer than rear made it feel like the rear was steering the bike over bumps. Now running 10# under max air on the tires, for solo riding, 7# in the forks. Rear XJ shocks at 22#, #3 dampening. Riding fairly smooth and still handles tight on curves.
Your symptom sounds like what I got when the heat (in OK) melted the sticky tape and I lost my wheel weights off the front. Out-of=roundness of tire or wheel might also do that. Speed related makes me think balance.

[a3dudek]

thanks for the opinion poprock, i am going to take my wheel in tomorrow to get balanced. i am hoping that will fix the problem. i am really hoping its not a bent / oblong rim.

[mjpxs11sh]

+

small world. i just started a thread with the exact same issue. the factory manual says 5.7psi for the frt shocks and i put 10psi in trying to see if i could correct the vibration issue and no change. let us know what u find out.