GS 1000 ST : the weave is back

[John Kat]

I just finished rebuilding my GS 1000 ST from the bare frame up and yesterday I went for my first ride.
Everything works fine except that in the medium fast to fast corners, the bike will go into a slow weave
Some of you might remember that I had this issue some time ago with the same bike until it disappeared after changing the fork tubes.
http://www.thegsresources.com/_forum/showthread.php?t=173347
The differences between yesterday and today are the following:
1) I went back to the 18*2.15 rear wheel versus the 17*3.0 GS 1100 wheel.
The rear tire is a 120/90*18 ContiGo versus a 140/80*17 BT45.
2) I went back to the original steel swingarm versus the Aluminum one from the GS 1100
3) the front mudguard was changed from the steel version to the plastic version coming from an 1100.
The test was done without the quarter fairing.
I'll reinstall the GS 1100 rear wheel first to see if it improves or not...
Here's a picture when 95% done

 

[John Kat]

Instead of changing the rear wheel, I started by installing a period fork brace.
Never thought they were really worthwhile but this was a good opportunity to test one
I also retorqued every nut and bolt and specially the swingarm where the slightest play can hurt the roadholding in a big way.
Now the road test!
Big improvement but the weave is still lurking it's ugly head when you roll off the throttle in the middle of medium to high speed corners
Another annoying trait surfaced as the rear tire is very sensitive to longitudinal road irregularities...
No doubt, I have to go back to the GS 1100 3" wheel with it's 140/80 BT 45 tire.
To be tested tomorrow if the weather allows.
Here's the brace and the before and after pictures of the rear wheel:

 

[oldgrumpy]

I just finished rebuilding my GS 1000 ST from the bare frame up and yesterday I went for my first ride.
Everything works fine except that in the medium fast to fast corners, the bike will go into a slow weave
Some of you might remember that I had this issue some time ago with the same bike until it disappeared after changing the fork tubes.
http://www.thegsresources.com/_forum/showthread.php?t=173347
The differences between yesterday and today are the following:
1) I went back to the 18*2.15 rear wheel versus the 17*3.0 GS 1100 wheel.
The rear tire is a 120/90*18 ContiGo versus a 140/80*17 BT45.
2) I went back to the original steel swingarm versus the Aluminum one from the GS 1100
3) the front mudguard was changed from the steel version to the plastic version coming from an 1100.
The test was done without the quarter fairing.
I'll reinstall the GS 1100 rear wheel first to see if it improves or not...
Here's a picture when 95% done

...................hi luv your tank!!!!!! regards oldgrumpy

 

[Kiwi Canuck]

Steering head bearings

Steering head bearings

Have you checked your steering head bearings? either loose or worn?

 

[Nessism]

Wheel alignment?

 

[Guest]

Tyre pressures ?

Cheers , Simon .

 

[GelandeStrasse]

Have you checked your steering head bearings? either loose or worn?

+1 for head bearings

 

[eddie21]

+1 for head bearings

+2 for the steering head bearings - my 79 1000S was very unstable until I had new ones installed. Felt like a different bike after that... in a GOOD way!

Hopefully it is that simple.:-\\\

 

[John Kat]

Thanks for the comments
The wheels were perfectly aligned, the head bearings are almost new, the tire pressures were checked before the ride...
I believe there is a mismatch between the front and rear tires having a BT 45 upfront and a ContiGo at the rear but before going for the ride with a BT 45 at the rear, I rechecked the tightening of the head bearings by carefully going through the proper sequence.
I want to demonstrate, I'm listening to you guys!
In any case, just back from the ride and...no weave anymore!!!
These GS 1000 STs are really some bike!
The engine just loves to rev and I can't imagine what the Yoshimura version was like in those days...
As a side note, I really love the Bridgestone BT 45s, you can lean and lean it over with great confidence and then feed in the power until the next corner.
A true pleasure.

 

[tatu]

Thanks for the comments
The wheels were perfectly aligned, the head bearings are almost new, the tire pressures were checked before the ride...
I believe there is a mismatch between the front and rear tires having a BT 45 upfront and a ContiGo at the rear but before going for the ride with a BT 45 at the rear, I rechecked the tightening of the head bearings by carefully going through the proper sequence.
I want to demonstrate, I'm listening to you guys!
In any case, just back from the ride and...no weave anymore!!!
These GS 1000 STs are really some bike!
The engine just loves to rev and I can't imagine what the Yoshimura version was like in those days...
As a side note, I really love the Bridgestone BT 45s, you can lean and lean it over with great confidence and then feed in the power until the next corner.
A true pleasure.

It'll be back don't worry.
Its the nature of the S, you think its ironed out then suddenly its back. My weave has not been back since I dropped the tyre pressures.

 

[posplayr]

It'll be back don't worry.
Its the nature of the S, you think its ironed out then suddenly its back. My weave has not been back since I dropped the tyre pressures.

I used to have a weave on my 83 GS1100E that seemed to be a combination of rear tire sidewall flex and soft rear springs.

It was most noticeable when going through an undulating road surface in a curve.

After upgrading to 4.5" wheel and 170/60-18" and stiffer Ohlins springs it has gone.

 

[John Kat]

I used to have a weave on my 83 GS1100E that seemed to be a combination of rear tire sidewall flex and soft rear springs.

It was most noticeable when going through an undulating road surface in a curve.

After upgrading to 4.5" wheel and 170/60-18" and stiffer Ohlins springs it has gone.

I fully agree on the sidewall flex beeing the major culprit.
You can imagine that a 120/90 tire on a 2.15" wheel is an invitation to disaster.
I could distort the tire just by pulling it sideways with the wheel on the bike
This would explain, I believe, why the phenomenon is worse at speed.
The tire gets distorted when in contact with the road but doesn't have enough time to settle by the next revolution.
It just gets worse from there onwards.
Would be nice to be able to catch it on a GoPro

 

[Kiwi Canuck]

It'll be back don't worry.
Its the nature of the S, you think its ironed out then suddenly its back. My weave has not been back since I dropped the tyre pressures.

Chris, what tyres and pressures are you running?

 

[John Kat]

It'll be back don't worry.
Its the nature of the S, you think its ironed out then suddenly its back. My weave has not been back since I dropped the tyre pressures.

That observation is in line with the sidewall flex made by Jim.
With less pressure in the tire you will decrease the energy stored in the tire when getting distorted and thus it will not kick back as badly.
Less weave for sure but for how long as you rightly point out???

 

[posplayr]

That observation is in line with the sidewall flex made by Jim.
With less pressure in the tire you will decrease the energy stored in the tire when getting distorted and thus it will not kick back as badly.
Less weave for sure but for how long as you rightly point out???

Mine was a very strange effect where if you were leaning into a turn and the road undulated such that the rear spring compressed more than the front the bike would lay down into the turn but come back up as the spring rebounded.

So high speed turns above 60-70 mph could be a little spooky at times. Below that there was not the same rear spring compression that seemed to manifest the feeling.

I theorised it was rear sidewall flex exceeding front side wall flex due to the banked turn while compressing the rear more.

I had all new bearings,alignments everything so it had to do with springs and tries and nothing else.

 

[Kiwi Canuck]

Matched tires and grip levels

Matched tires and grip levels

I have heard that the new grippier tires can cause the frame to flex more as they exert more stress and forces on the frame than the original tires, which could cause the symptoms described.

When I was racing the GS1000's we pretty much only played with tire pressures, shock and fork settings. Never really had an issue as I recall with the bike weaving but I didn't know any better, just rode it as hard as I needed to.
But I do remember spending a lot of time with the mechanics going over tire pressures and trying various combinations when we needed to gain some speed or it was an important race.

 

[Sandy]

It took me quite a while to dial in the handling on my '79 GS1000N. The setup I found that works for me is Progressive springs up front with no air, 15W fork oil, 100/90x19 Dunlop GT501 at 34 lbs. and a Tarozzi fork brace. The rear still has, believe it or not, the stock shocks (it's a low mileage survivor) with the spring set on firm, damping all the way up and a 120/90x18 GT501 at 38 lbs. The rear works great for solo riding but that's it, no adjustment left. I'm a believer that suspension set too stiff can be as big or bigger problem than suspension set too soft. Reason being if it's too stiff on these old bikes it transfers too much stress to the frame/swingarm and can induce flexing. Suspension has to be able to work to do it's job. That said the damping has to match the spring rate that has to match overall weight and riding style and also be balanced front to rear ...sigh. Can be a lot of fiddling, change one thing then you most liking have to revisit the rest. Case in point was when I installed my fork brace the bike felt better even at low speed but when I first pushed it hard it developed a fast oscillation that wasn't there before, turns out the front steering head bearing needed a minor retorque and all was well. You mentioned low speed weave. Generally low speed weave is a symptom of something not right in the rear and higher speed oscillation is something in the front. For an old bike it handles extremely well. It doesn't feel like it's on rails like the modern stuff but you have to be riding on the edge and encounter some good road irregularities to make it wiggle much. Sounds like you got it mostly sorted, hope it stays that way.

 

[bonanzadave]

Can be a lot of fiddling.

Im getting tired of fiddling.....

With everything mentioned in this thread and more my bike feels just like it did with old suspension and tires. Stock (35k miles) shocks and worn out Dunlop Elites. Now its got new Progressives and Avons, AllBalls in the head and new swing arm bearings and fork bushings. Same weave.

The head is adjusted just tight enough so it wont wander going slow. One click tighter and you can feel it at 5mph. Backing it off causes the high speed weave to go nearly tank slapper.

Im running the Avons at 35 psi cold and all suspension pre-load and dampening is about in the middle.

Strange :-k.

 

[John Kat]

It took me quite a while to dial in the handling on my '79 GS1000N. The setup I found that works for me is Progressive springs up front with no air, 15W fork oil, 100/90x19 Dunlop GT501 at 34 lbs. and a Tarozzi fork brace. The rear still has, believe it or not, the stock shocks (it's a low mileage survivor) with the spring set on firm, damping all the way up and a 120/90x18 GT501 at 38 lbs. The rear works great for solo riding but that's it, no adjustment left. I'm a believer that suspension set too stiff can be as big or bigger problem than suspension set too soft. Reason being if it's too stiff on these old bikes it transfers too much stress to the frame/swingarm and can induce flexing. Suspension has to be able to work to do it's job. That said the damping has to match the spring rate that has to match overall weight and riding style and also be balanced front to rear ...sigh. Can be a lot of fiddling, change one thing then you most liking have to revisit the rest. Case in point was when I installed my fork brace the bike felt better even at low speed but when I first pushed it hard it developed a fast oscillation that wasn't there before, turns out the front steering head bearing needed a minor retorque and all was well. You mentioned low speed weave. Generally low speed weave is a symptom of something not right in the rear and higher speed oscillation is something in the front. For an old bike it handles extremely well. It doesn't feel like it's on rails like the modern stuff but you have to be riding on the edge and encounter some good road irregularities to make it wiggle much. Sounds like you got it mostly sorted, hope it stays that way.

Fully agree with what you say: the suspension must be allowed to do it's job.
I personally use the second preload at the rear with the 2nd damping level.
It suits my 73 kg weight nicely and keeps me away from the chiropractor as there are many poor roads around here
The GT 501s are also good tires that appear to have much stiffer sidewalls than the ContiGo. My GS 1000 EC is shod with a pair of these but in 130/90*17 at the rear. Never a hint of weave on that bike!

 

[John Kat]

I have heard that the new grippier tires can cause the frame to flex more as they exert more stress and forces on the frame than the original tires, which could cause the symptoms described.

When I was racing the GS1000's we pretty much only played with tire pressures, shock and fork settings. Never really had an issue as I recall with the bike weaving but I didn't know any better, just rode it as hard as I needed to.
But I do remember spending a lot of time with the mechanics going over tire pressures and trying various combinations when we needed to gain some speed or it was an important race.

You most probably used racing slicks with a much lower profile than the /90 used on the street bike.
John Ulrich wrote in a Cycle World test of the Yoshimura GS 1000 "When I rode the Suzuki at Riverside it wobbled fiercely, yet at Willow the handling was faultless"
A strange machine the GS 1000 S but what a pleasure when you get it right