Feels like oscillating

[alke46]

Today was my 1st ride since upgrading the suspension on the GS. Have installed new Hagon shocks on the rear, set to the middle of three settings and new sonic straight rate 1.1 springs in the front forks. 10 wt. fork oil. Currently running Shinko Tour Masters with less than a thousand miles on them. Still have the nubs on them.

On a road with some moderately sweeping curves, I found when taking a left sweeper, the bike felt good. The issue was when taking a right curve at aggressive speeds the bike felt like the front end was oscillating. And if the road surface had any sort of roughness the feeling was darn near scary.

I need help sorting this problem. Is this a problem that a fork brace would correct or am I looking at something else to fix the oscillating feeling?

Thanks for reading.

[alke46]

Just as a side note, the whole suspension feels a bit stiff to me. Small bumps in the road feel rather harsh. I think I need to go down to the 1.0 springs.

[mmattockx]

What are your laden sag numbers? It is hard to say much without knowing that as a starting point.


Mark

[alke46]

Sag is good at only 1/4". Before the new upgrades, the sag was 1/2".

[Ray916MN]

Are the steering head bearings and swingarm bushings in good shape?

Static sag typically should be about 1.25" (~ roughly 1/3 the total suspension travel) measured from full extension to settled while sitting on the bike without it being on a stand.

[alke46]

Can't answer for certain about the bearings. I have not done any checking personally but I do know when traveling at just about any speed, if I take my hands off the handlebars, there is no wobble at all and no pull to either side. It just continues on a straight path as though I never let go of the bars.

Concerning the sag, I contacted Jeff at Sonic and he never stated the need for more sag. He just told me that the new springs would definitely be stiffer than the old 37 year old originals. As I mentioned, I think I need to go down to the 1.0 springs. Just a hunch on my part.

[Ray916MN]

Can't answer for certain about the bearings. I have not done any checking personally but I do know when traveling at just about any speed, if I take my hands off the handlebars, there is no wobble at all and no pull to either side. It just continues on a straight path as though I never let go of the bars.

Checking the bearings is easy.

Put the bike on the centerstand. Grab the rear wheel and try to shove it side to side. If you feel any movement, the swing arm bearings/bushings are bad. When these go bad the bike will oscillate when in sweeping turns with a trailing throttle. Applying the gas typically helps reduce the oscillation.

To check the steering head bearings, get the front wheel in the air (eg. have someone sit on the rear seat while the bike is on the center stand). Grab the lower fork legs and try to move them backwards and forwards. Movement indicates the steering head bearings are bad. Move the steering through its range paying particular attention to how it feels when crossing the straight ahead position. Any feeling of notchiness and the steering head bearings are bad.

[alke46]

Yes I understand about the testing for wear, I just have not done it yet. Will do tomorrow and report what I find. Thanks.

[posplayr]

Are the steering head bearings and swingarm bushings in good shape?

Static sag typically should be about 1.25" (~ roughly 1/3 the total suspension travel) measured from full extension to settled while sitting on the bike without it being on a stand.

And that is only one end.

[Sandy]

Sounds like you don't have enough sag, as mentioned it should be about an inch give or take. Suspension HAS to be compliant to work, too stiff can be worse than too soft with these old bikes. Too stiff can transfer too much load to our flimsy frames. A common mistake in chasing down wiggles and wobbles can be assuming it's front end related. Sound like you have too much spring on the front and not quite enough damping which can cause some funky problems. The setup the works for me on my '79 GS1000 is Progressive springs which are probably a little soft for me (200lbs on a good day) and maybe equivalent to a 1.0 Sonic or maybe even a bit less and 15W fork oil give it a little more dampening over stock. Sag would be around an inch give or take and doesn't bottom under extreme braking. Put some tie wraps around your fork tubes to measure what's happening.

[mmattockx]

Sag is good at only 1/4". Before the new upgrades, the sag was 1/2".

Concerning the sag, I contacted Jeff at Sonic and he never stated the need for more sag.

I was talking about laden sag, which is measured with you sitting on the bike in your riding gear. You want the front sag to be ~25-28% of total fork travel and the rear to be 30-35% of rear travel. For my 82 1100E that equates to around 40-45mm of sag in the front and 30-35mm in the rear. Adjust accordingly if your suspension travel is significantly different than mine. You will need help to measure laden sag, it is at least a 2 person job and a third to balance the bike while you sit in your riding position doesn't hurt. When you measure the laden sag make sure you bounce the end you are measuring a few times to let it settle with as little stiction effect as possible. In front you adjust the sag by cutting your preload spacers to whatever length you need to get the desired amount. In the rear you use the preload adjuster on the shocks.


Mark

[alke46]

OK here is what I have as of now. "Laden" sag is only 3/8" on front forks. The swingarm feels like new, no looseness at all. The forks move full turn right to left very freely with no feel of any notching anywhere, however, grabbing the bottom of the fork legs I can detect a very slight movement forward to backwards. I would say it moves 1/16" or less. Not much but maybe could be causing this condition?
I think my next move is to change the spacer in the forks to create more sag.

[bonanzadave]

I can detect a very slight movement forward to backwards. I would say it moves 1/16" or less.

Did you change the bushings in the forks. When I read your first post I thought you were talking about your Honda. Police STs in the UK had issues with high speed wobbles.

[Ray916MN]

OK here is what I have as of now. "Laden" sag is only 3/8" on front forks. The swingarm feels like new, no looseness at all. The forks move full turn right to left very freely with no feel of any notching anywhere, however, grabbing the bottom of the fork legs I can detect a very slight movement forward to backwards. I would say it moves 1/16" or less. Not much but maybe could be causing this condition?
I think my next move is to change the spacer in the forks to create more sag.

Should be zero movement grabbing the front forks and moving them backwards and forwards. Steering stem nut isn't properly tensioned. Tighten it to the proper torque and try the front steering head bearing check again. My bet is you'll feel notchiness as the steering moves through the center. Without proper torque on the steering stem nut you don't feel the notchiness because the front end is hanging on the top stem bearing. When the bike is loaded, most of the load gets taken by the bottom bearing. When the steering stem isn't properly torqued, the steering stem moves up and down when you hit bumps, smacking and flattening the lower steering head bearing and race. Properly tightened, you feel the ruined bearings because the steering stem is now supported by both the upper and lower bearings. Bad steering head bearings can definitely be the source of your problems.

With respect to measuring sag, make sure you are measuring the sag from when there is absolutely no load on the front end (full extension) to when the bike is sitting on its wheels only with you on the bike and your feet off the ground. Takes at least 2 people if not 3 to do this properly.

[Nessism]

1.1's are pretty stiff. Did you go though the spring calculator on the Sonic website?