Getting a GS 1000 S to handle

[John Kat]

For the last couple of months, I've been fighting to get my GS 1000 ST ( 2nd gen) to handle properly.
The bike has been rebuilt the ground up with the frame checked.
It started 100% stock except for the Koni rear shocks.
My references for roadholding ( of this period) are a 100% standard GS 1000 EC and my GS 1000 XP I've described in another thread with GSX R 1100 suspensions and wheels.
The issue was related to a slow weave that could start in medium to high speed corners ( above 70 mph) but also in straight lines above 90 mph.
No fun at all on a bike that really wants to go faster.
I started changing the components hereafter the one after the other:
1) rear wheel from 18" with 120/90 tyre to 17" GSX 1100 wheel with 140/80 tyre
2) decrease front fork pressure to about 7psi
3) replace rear swinging arm with a GS 1100 Katana aluminum arm
4) reduce preload on Koni shock absorbers to lowest position
All of these changes allowed me to feel more confident in slow turns but as soon as the speed went up here came the weave again...
Finally, I decided to take my quarter fairing off more to determine if the forks were straight than anything else.
Guess what? The nasty weave has gone away
I can now enter the fastest turns with the confidence that the bike won't shake it's head.
What I don't know is whether this issue is purely aerodynamic or a question of added mass to the front fork that amplifies any disturbance from the front end?
It could also be a combination of both?
I want to point out that I ride without a steering damper.
Has anyone else experienced this?
My next move is to install a Racetech "Gold valve cartridge emulator" as I believe there is far too much compression damping up front.

[Big T]

Weave is generally from:

1. Wheel misalignment
2. Too soft fork springs
3. Sticky fork tubes - are you running a fork brace?
4. Bad wheel bearings
5. Bad tire

Since you don't mention upgrading your forks, I'm thinking #2.

[Rover]

If it was the fairing,one would assume that other bikes with that or similar fairing would also have this instability?

[John Kat]

The only remaining difference to my GS 1000 EC is the front fork springs that are specific to the 2nd gen GS 1000 ST.
I don't know if they are stiffer or not?
In any case the stiffness can be modulated by the amount of air in the forks.
I tried high and low pressures: no change!
The front tyre is new.
There is a fork brace in place.
I checked the wheel alignment and I measured 0.62 degrees off vertical between the front and rear wheels.
Apparently less than 1 degree is OK?
There appears to be no issue with the wheel bearings ( no lateral play whatsoever).
No, I really believe there is an issue with the fairing!
Interestingly enough the bike was fitted with a steering damper when I bought it?
Was this standard? I don't know?

[850 Combat]

I own a Norton Commando that used to weave with a headlight fairing in the 70's. I took it off and the weave went away. Later I tried a different handlebar fairing, and the problem did not come back.

This same motorcycle is extremely sensitive to rear tire wear. When the rear tire would get a small flat area worn in its center, the bike would develop a high speed slow weave that was quite frightening, particularly if I tried to continue to accelerate through it. I switched rear wheels on it to allow more selection in tires, and have not had the problem.

[John Kat]

I owned a Norton Commando myself when I was young and I can still remember when the front fork hit the stops both left and right in a 100 mph bend....
I don't know why I didn't fall off???
I appreciate your comment about the rear tire.
Allthough this is the second tire I'm testing,I will swap wheels with my GS 1000 EC that has a brand new GT 501 tire.
I will also revert to the original rear shock absorbers as I don't really like the progressive springs on the Konis ( 100 to 185 lbs/inch !!!)

[posplayr]

I own a Norton Commando that used to weave with a headlight fairing in the 70's. I took it off and the weave went away. Later I tried a different handlebar fairing, and the problem did not come back.

This same motorcycle is extremely sensitive to rear tire wear. When the rear tire would get a small flat area worn in its center, the bike would develop a high speed slow weave that was quite frightening, particularly if I tried to continue to accelerate through it. I switched rear wheels on it to allow more selection in tires, and have not had the problem.

That would be my guess as well; I would go through whatever mod you are willing to make as most will help; wider wheels and lower profile radial tires will help the most. There is so much interaction, trying to do this step by step is not going to tell you much.

[gshub]

Theres nowt wrong with handling of a Gs1000s if its set up properly, mine got a strengthend frame, Gsx1100kat swinging arm ikon shocks, Avon road rider Tyres 130/90/17 rear ,i know it should have a 120/90/18 it sit in my garage thats where its staying.
100/90.19 front, a balancer on fork legs so air preasures are the same 11/12psi .
worst thing is over tight head race bearings.
normaly tyres preasures are 33front, 38back.
also got a micron fork brace fitted.
you deffently dont need a steering damper on the road.

[81ZUKI75]

The only remaining difference to my GS 1000 EC is the front fork springs that are specific to the 2nd gen GS 1000 ST.
There is a fork brace in place....

No, I really believe there is an issue with the fairing!
Interestingly enough the bike was fitted with a steering damper when I bought it?
Was this standard? I don't know?

Well I don't know much about the 1000's...BUT if I was fortunate enough to have two so similar (GS 1000 EC,GS 1000 ST) I'd be swapping that fairing over to the '78 model just for grins and giggles . That might just clear the fairing of any wrong-doing if the behaviour doesn't move with it.

I don't believe that steering damper is "stock" so you've got to wonder why it was installed. I'd pull the fairing, fork brace, fender, and wheel and check the forks tubes for alignment to themselves and for stiction. Re-install everything in the reverse order checking the fork at each step. Hopefully somewhere in all the checks something will show up.

[TheCafeKid]

Have you checked wheel alignment? Head bearings? Replaced or need tightened? Check for tweaks in the fork assembly? Check the frame? Fork that are sticking can also lead to weave. Also did you assure that you corrected the spacers on the axle/back end for a wider wheel? They're likely different than stck depending on the width of the hub. I swapped to a 3.5" wide 1150 wheel on my 1100E and had to do a fair bit of correction. I think it ended up being an added .050" inboard of the caliper hanger and .025" outboard. If not you may not have enough thread left to properly squish the swingarm down. That will allow the rear wheel to walk on the axle, ruin your bearings, etc etc. Braking with rear will mKe it especially noticeable.

[GregT]

Was the fairing frame mounted or mounted to the forks ?

If fork mounted, there's your answer - too much mass on the forks which will magnify any existing problems and cause more too....

With our race 1000 we found the springs supplied with the Konis were far too stiff - no static sag even with the rider aboard....if there is a rear tyre problem, too stiff rear suspension is going to exagerate it.

Change the fork springs to Progressive and forget the air assist. For even race track use the standard damping with forks in good condition is perfectly OK.

Vertical wheel alignment within one degree is very good for the standards of the day, certainly quite acceptable. What misalignment is left is probably in the swingarm - they often take a pemanent "set"

[John Kat]

Many thanks to all for the valuable comments.
I've tried to use a scientific approach to this issue by changing only one parameter at a time.
As it stands today, the quarter fairing ( attached to the front fork) makes a night and day difference in roadholding.
As the GS 1000 S came out the factory likes this, the question is: did Suzuki let such a poor handling bike out and hope they would get away with it or is it only my bike that has the issue?
I found the answer in an original copy of a french magazine ( Moto Journal dated sept 20 1979) that clearly thought the bike had a high speed handling issue.
According to them the problem came from the fact that the side wings on the fairing push the front end downwards at speed , thus reducing the travel. They corrected this by adding a 30 mm spacer on top of the springs and putting a 50% mixture of ATF and 20W/50 oil in the fork legs. This modification allowed them to clock the bike at 220 km/h...
Another option according to them would be to lengthen the forks tubes by the same 30 mm.
Strangely enough this is what Yoshimura did on Wes Cooley's racing bike...

[posplayr]

Many thanks to all for the valuable comments.
I've tried to use a scientific approach to this issue by changing only one parameter at a time.
As it stands today, the quarter fairing ( attached to the front fork) makes a night and day difference in roadholding.
As the GS 1000 S came out the factory likes this, the question is: did Suzuki let such a poor handling bike out and hope they would get away with it or is it only my bike that has the issue?
I found the answer in an original copy of a french magazine ( Moto Journal dated sept 20 1979) that clearly thought the bike had a high speed handling issue.
According to them the problem came from the fact that the side wings on the fairing push the front end downwards at speed , thus reducing the travel. They corrected this by adding a 30 mm spacer on top of the springs and putting a 50% mixture of ATF and 20W/50 oil in the fork legs. This modification allowed them to clock the bike at 220 km/h...
Another option according to them would be to lengthen the forks tubes by the same 30 mm.
Strangely enough this is what Yoshimura did on Wes Cooley's racing bike...

Well yes, I have heard of similar issues but if you did the progressive springs and/or RT emulators (and or change the tires) it would have potentially gone away as well.

There is a need to balance the response of the front and rear to road inputs. General Frt/Rear imbalance can cause oscillation.

[John Kat]

I ordered some RaceTech springs today to get rid of the uncertainty of the air in the front forks.
I also checked the parallelism of the fork tubes with a 10 cm glass plate.
On my GS 1000 ST the gap is 0.20 mm.
On my GS 1000 EC the gap is 0.15 mm.
I suppose these values are within tolerance?

[TheCafeKid]

Again I will ask, did you assure that the squish in the swingarm was adequate to sandwich everything together?? While the hub on your "new" rear wheel may look the same, it may not be the same depth as the original. This is actually pretty common in the GS line from model to model. A lot of the bikes rear spacers are not the same width. I misjudged that myself and had as little as .075" of play left on the axle, side to side, and it made the bike VERY squirelly. If you run out of threads before the axle nut can compress the swingarm, the rear wheel may walk on the axle.

Your forks may have some to do with it. It's hard to tell over the web, without riding ourselves, which end it actually is coming from. It can be difficult to discern which end is causing the waggle period. The both work together to make the bike track correctly. Just give it a look.

Btw that should read seventy five thousandths. I missed a zero