Bike starts to "wobble" at higher speeds?

[posplayr]

Daltydog runs his avons at high 30-40 psi also your bike is not the same as it was 30 years ago . Springs Sag unless you have changed them. one last thing u said the guy that changed your tires said bearings were fine? Did he know u were praticing for the 24 hour speed record.how many miles on the bike ? What suspension modsz/refurb have you done?

 

[tkent02]

Actually, if a tire had 4 digits after the DOT, it would have been produced with in the last decade. All tires before 1999 or 2000 used 3 digit tire codes. So a tire produced the first week of 1978 would be written as 018. But the 8 could mean any decade ending in 8. That's probably why they changed the standard in 2000.

Except tires didn't have date codes in 1978.
Check your wheel bearings, too. In all likelihood the swingarm, steering head and wheels all have bad bearings. That stuff is all thirty years old.

 

[bonanzadave]

your bike is not the same as it was 30 years ago .

Jim, I think thats it in a nutshell. Im a selfish person to go out and act like some irresponsible kid breaking the law which would put my family in a very bad way if something went wrong. So should I just stop 3 digits ? Easy answer.....or is it ?........

Back on topic.....

The Guy who did the tires is a speed freak. I wont go into his bio. Its right here http://riverszzr.webs.com/
I was surprised he didnt ask about the wheel bearings. 35K on the bike but its a different front wheel. It did the same thing with the orig wheel tho. When I brought it up we looked them over and decided against doing them. He took the tubes out with the old Dunlaps. Cleaned up the rims and put the Avons on tubeless. Note to self: Check the tire pressure again. I forgot to mention: On last nights run I has 15psi in the forks.
Mods ? Everything on your list. Progressive frt & rear. All balls head bearings. Swing arm bearings. Fork seals and 10/15 wt fork oil. Every bolt and nut checked. Every adjustment set on 2 (frt fork pre load & dampening, back shock spring height). I would like to revisit the string alignment. I dont think I have that down to a science. When I did it both chain adjuster marks were right on 5 and a half.

Side note: I have a friend that was crewing out at Bonneville last summer. :-k

In all likelihood the wheels all have bad bearings. That stuff is all thirty years old.

Tom, I will get new wheel bearings....

What do you think about the saddle bags causing speed issues ?

 

[tkent02]

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Tom, I will get new wheel bearings....

What do you think about the saddle bags causing speed issues ?

I would say not likely with a tight bike but possible, aerodynamics is weird science.
I put a small tank bag on my BMW with a big fairing and got helmet buffeting. I don't know how a bag on a tank behind a big fairing can cause buffeting, but it did. Weird science.

More likely worn bearings are allowing the problem, and the bags trigger it.
Check all the bearings, even without that trigger, something else might do it.
Rain grooves got my old Yamaha 650 going once.
Speed wobble crashes are bad ones.

 

[posplayr]

Jim, I think thats it in a nutshell. Im a selfish person to go out and act like some irresponsible kid breaking the law which would put my family in a very bad way if something went wrong. So should I just stop 3 digits ? Easy answer.....or is it ?........

Back on topic.....

The Guy who did the tires is a speed freak. I wont go into his bio. Its right here http://riverszzr.webs.com/
I was surprised he didnt ask about the wheel bearings. 35K on the bike but its a different front wheel. It did the same thing with the orig wheel tho. When I brought it up we looked them over and decided against doing them. He took the tubes out with the old Dunlaps. Cleaned up the rims and put the Avons on tubeless. Note to self: Check the tire pressure again. I forgot to mention: On last nights run I has 15psi in the forks.
Mods ? Everything on your list. Progressive frt & rear. All balls head bearings. Swing arm bearings. Fork seals and 10/15 wt fork oil. Every bolt and nut checked. Every adjustment set on 2 (frt fork pre load & dampening, back shock spring height). I would like to revisit the string alignment. I dont think I have that down to a science. When I did it both chain adjuster marks were right on 5 and a half.

Side note: I have a friend that was crewing out at Bonneville last summer. :-k



Tom, I will get new wheel bearings....

What do you think about the saddle bags causing speed issues ?

As far as triple digit testing...... Ya gotta do some testing just to insure the bike is safe. Just don?t make it too much of a habit

Sounds like you have been through most things. The alignment might be out a bit using swing arm marks. The string method is relatively simple. You are just extending strings froward from the rear wheel that are both parallel to the rear wheel (either side).

In this way the front wheel should be both aligned and right in the center of the two strings that are projected forward. In order to determine if it is centered and aligned though you need four equal measurements both front and back of rotor and left and right side rotors. That is so that you get the front forks straight and centered.

You have not really described the wobble. Is it from the front or the rear? Is it handlebar shake (like a tank slapper) or rear end "wobble".

If the tank bags were sticking pretty far out into the free stream velocity, then they could start developing what is known as a "vortex street"

http://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_vortex_street

When you have a "bluff body" (a rounded shape like a saddle bag), then there is a tendency for the flow to alternating shed from one side to the other. When the shedding occurs there is a increased pressure drag associated with the low pressure in the separated flow area. The alternating side to side drags, coupling with rear wheel side wall flex could be causing the issue.

I have noticed a lot of lateral dynamics on my ED, in curves from having a tall 130/90-17 tire coupled with slightly soft rear springs.

Any how without getting into a whole lot more conjecture I would not change anything else and just take off the bad and see it reduces the effect.

You can always come back and do the wheel alignment, but doing one thing at a time helps narrow down teh different factors.

 

[bonanzadave]

You have not really described the wobble. Is it from the front or the rear?

Dont know front or rear. Its as if the thing were on a hinge. Not head shake. A kind of come on slow weave.....

 

[posplayr]

Dont know front or rear. Its as if the thing were on a hinge. Not head shake. A kind of come on slow weave.....

Sounds like the rear then ; dont change anything but drop those bags and see if it helps

 

[posplayr]

We talking about these bags?

http://www.thegsresources.com/_forum/album.php?albumid=309&pictureid=1608

The main issues I had with rear wobble was too much weight and being in a undulating turn. Doesn't sound like what you are describing.

Are you carrying any weights in there ?

 

[bonanzadave]

We talking about these bags?

Yep ! and now I got a gay-rod sissy bar and a bowling bag on the back. Dont really carry any weight except for a small tool kit and a rain suit. I got the bags so I can ride the bike if the wife sends me out for grocery's .

 

[bonanzadave]

Last night I stretched a string to check wheel alignment. Around the back tire and up to the front. I spread the string apart up front so when it passed the forward sides of the rear tire it just touched but did not deflect. I then measured the gap between the string and the front tire. Both sides forward and both sides aft were the same gap. Does that sound close ?

Checked the tire pressure. 35psi in both. The 15psi I put in the forks is still there too even with a pitted fork tube. Took the Saddle bags off but left the tail pack on. Went for a "run". It felt pretty good on one pass. When it started to buffet a bit I tucked in and the buffet went away so I rolled in some more gas. I got going so fast I blew right by my exit. Coming back It started to "dance" a little at 5K so I backed off and went home. Funny thing on that last pass I had my feet on the back pegs......:-k

 

[posplayr]

Last night I stretched a string to check wheel alignment. Around the back tire and up to the front. I spread the string apart up front so when it passed the forward sides of the rear tire it just touched but did not deflect. I then measured the gap between the string and the front tire. Both sides forward and both sides aft were the same gap. Does that sound close ?

Checked the tire pressure. 35psi in both. The 15psi I put in the forks is still there too even with a pitted fork tube. Took the Saddle bags off but left the tail pack on. Went for a "run". It felt pretty good on one pass. When it started to buffet a bit I tucked in and the buffet went away so I rolled in some more gas. I got going so fast I blew right by my exit. Coming back It started to "dance" a little at 5K so I backed off and went home. Funny thing on that last pass I had my feet on the back pegs......:-k

How close, normally you would be a few mm out? You want to be within 1-2 mm.

So it felt about the same?

Anyway sounds like you are close.

Are you carrying any errr..... extra weight on the rear (as compared to 30 years ago:-\\\)?

Bumping up the preload a bit on the rear might help some. I also had my front fork with a lot of preload.

 

[bonanzadave]

Are you carrying any errr..... extra weight on the rear (as compared to 30 years ago:-\\\)?

Extra cargo ? Ha ! No, like then Im still about a buck 8E.

New revelation. A friend stopped by to do a carb sync (the guy who crewed at Bonneville) and we looked at the rear end in motion on the centerstand. There is a little side to side movement. I want to find an runout caliper and show you guys a video......Stiff link in the chain ?

 

[Calvin Blackmore]

not sure if its been covered but dynamically balanced wheels greatly enhance a bikes ability to feedback actual road response.

I went for years thinking an annoying reverb in my spine was the price of two wheeled glory

had a spin blance and it was like oh my god

I jus tmean that the added vibration can impact on other sources and confuse you.

 

[posplayr]

not sure if its been covered but dynamically balanced wheels greatly enhance a bikes ability to feedback actual road response.

I went for years thinking an annoying reverb in my spine was the price of two wheeled glory

had a spin blance and it was like oh my god

I jus tmean that the added vibration can impact on other sources and confuse you.

I would figure out why the wheel is wobbling though; Is it out of round or bent?

If you have that kind of imbalance you vant fix, maybe this would help.

http://gl1800riders.com/forums/showthread.php?t=201280

 

[Calvin Blackmore]

I would figure out why the wheel is wobbling though; Is it out of round or bent?

If you have that kind of imbalance you vant fix, maybe this would help.

http://gl1800riders.com/forums/showthread.php?t=201280

nope just good old improperly mounted tire witht he heavy spot enhancing the wheeels heavy spot

Does the spot go opposite the stem
so hard to gauge when you are eaten by flies and anxious to ride

 

[bonanzadave]

I would figure out why the wheel is wobbling though; Is it out of round or bent?

If you have that kind of imbalance you vant fix, maybe this would help.

http://gl1800riders.com/forums/showthread.php?t=201280

Very interesting :-k. Have yet to explore the dial caliper on the rear wheel. Still planning it tho...

Update: Made a couple runs last night with the Bags on. Not good. I thought for sure I lost air in the fork with the leaky seal. Nope. I de-aired them both and tried it again. Still bad. Got to looking at the front end and discovered the 4 bolts (up under the fender) holding the horseshoe brace were loose . This is it ! I found the missing piece ! Got those tightened up and went out again. Still bad. I went home and parked the POS. dejected .

 

[gs road racer]

Dave go here long read but may help you...

http://www.bikesetup.com/

 

[bonanzadave]

http://www.bikesetup.com/

Thanks RRer,

I just stopped working for 45 min . Thats a great site ! The newbie page & riding tips should be read by everyone on 2 wheels. The info in Braking could save your life.

Im gonna study the Setup & Suspension stuff a little more to see if it relates to my wobbles. This line got my attention..."The geometry makes a huge difference but for the most part the manufacturers have done the work for you already." I always come back to this cause out of the box this bike was rock solid at 3 digits. I gotta be missing something.....

 

[posplayr]

Dave,
I have scanned back over the thread. and see a couple of things. You say you are putting 15 psi of air into the forks. I would not run any pressure but instead add a section of PVC if you have to to increase preload.
This makes me also wonder if you have set your preloads or on the rear if you might not have the right spring on that progressive. To light of spring on the rear can give issues as well. So measuring sag would be the best way to see where you are at and then go from there.

Another thing about those bolts on the fork that were loose. Do you have a fork brace? If so did you ensure that the entire thing slides up and down (with the springs out) before tightenting? My GS750 had a very strange feel up front (like the front tire was hunting left to right about 1") to it when I first got it ; after a change of oil and setting the fork brace much of that disappeared.


Jim

 

[gs road racer]

Thanks RRer,

I just stopped working for 45 min . Thats a great site ! The newbie page & riding tips should be read by everyone on 2 wheels. The info in Braking could save your life.

Im gonna study the Setup & Suspension stuff a little more to see if it relates to my wobbles. This line got my attention..."The geometry makes a huge difference but for the most part the manufacturers have done the work for you already." I always come back to this cause out of the box this bike was rock solid at 3 digits. I gotta be missing something.....

Exactly and as POS put it sag is where to start as it determines ride height, that site is a great resource for all.