Getting a GS 1000 S to handle

[Roger P.]

The fork mounted fairing on the 900 Seca was responsible for more than a few brown trouser moments as well. The switch to a new frame mounted unit apparently solved the issue.

 

[gs58]

I have ridden my '79 GS 1000S at 210 kph without any noticable weave or other issues. The fairing would be the same as yours and mounted to the triple clamps as your is. I think that your problem is somewhere else, but it may be exaggerated by the fairing.

 

[TheCafeKid]

I'm not sure I understand your point Caf?Kid?

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.

I replaced the original 18" GS 1000 ST wheel with a GSX 1100 17" wheel complete with it's axle and spacers.
There was no need to change any spacer as the width of the steel swinging arm is exactly the same as the aluminum one ( to the nearest mm).
I torqued the rear axle to the recommended value and there is no play whatsoever.
Where do you measure the .075" play?

I wasn't sure if you'd used the matching axle and spacers.

Like I said I did an 1150 3.5" wheel conversion on my 1100ES. The wheels were the same appearance wise aside from the rim being wider and the Hun being narrower than the OEM wheel. I didn't have the 1150 spacers etc so I had to use the 1100 stuff. The axle was too long for the hub of the rim, and with the OEM spacers you ran out of thread on the axle to sufficiently tighten the swingarm, thus a near invisible amount of slop. It became quite apparent while cornering hard and at high speed and was downright scary under heavy rear brake. I ended up having to add 25 thousandths inboard of the caliper hanger and fifty thou outboard and she was all good. That's all inwas talking about. But obviously that's probably not your issue here

 

[John Kat]

I have ridden my '79 GS 1000S at 210 kph without any noticable weave or other issues. The fairing would be the same as yours and mounted to the triple clamps as your is. I think that your problem is somewhere else, but it may be exaggerated by the fairing.

I agree.
My next test will be with Racetech .95kg/mm springs in the front forks.
Interestingly enough, the GS 1000 ST springs are not the same as those mounted in the original GS 1000 S.
In fact when I bought the bike there was one fork leg with one type of spring and the other with the longer ST type.
I suppose this was done after a crash?
This has been corrected of course!
The question is: are the hydraulics the same on the two legs?
I compared the "fork cylinders" ( PN 51146-49000) and there were identical but what about the fork tubes themselves?
As far as I understand the compression damping is controlled by the holes in the "fork cylinders" and the rebound damping by the valves at the bottom of the fork tubes?
By the way, I also use a fork brace that should (?) minimize any unbalance between the fork legs.
Next update following the test with the Racetech springs.

 

[sharpy]

How bad was the crash? And did u get my pm? Inner fork tubs are the same. whats the codition of your tyres? Worn tyres wont help one bit.

 

[John Kat]

An update on my roadholding problems on my GS 1000 ST.
The problem seemed to be due to the bikini fairing but following a new test with another front tire I discovered that the weaving was still there in long sweeping turns allthough I was riding without the fairing
The current front tire is a BT 45 F 100/90*19 V rating.
I still plan to test the bike with RaceTech springs upfront but the french importer isn't responding since I placed my order 6 weeks ago
The problem is really puzzling me as my two other GS 1000's don't have the issue.
Until I get the front springs, I'm going to go back to the OEM rear shocks instead of the Konis that are fitted currently.
I get the feeling that as soon as the rear goes over a bump in a fast corner, the weave starts?

 

[posplayr]

An update on my roadholding problems on my GS 1000 ST.
The problem seemed to be due to the bikini fairing but following a new test with another front tire I discovered that the weaving was still there in long sweeping turns allthough I was riding without the fairing
The current front tire is a BT 45 F 100/90*19 V rating.
I still plan to test the bike with RaceTech springs upfront but the french importer isn't responding since I placed my order 6 weeks ago
The problem is really puzzling me as my two other GS 1000's don't have the issue.
Until I get the front springs, I'm going to go back to the OEM rear shocks instead of the Konis that are fitted currently.
I get the feeling that as soon as the rear goes over a bump in a fast corner, the weave starts?

I have issues when the rear shocks are undersprung that sound similar to yours.

 

[John Kat]

It's good to hear that someone has the same issue !
I noticed that your bike is fitted with Ohlins shocks?
Are you able to adjust the compression and rebound damping separately?
Do you believe the issue is related to too much compression damping or too little rebound damping?
In the 80's the engineers used shocks with very little compression damping and harder springs that in turn required more rebound damping.
Not a good idea, compounded by the fact that the first "mag" wheels were massively heavy thus making it more difficult for the suspension to control all this unsprung mass !

 

[bonanzadave]

It's good to hear that someone has the same issue !

Search Wobble or Weave. You are not alone. I cant find my thread. I think 2008 got purged... ??...anyway yes, my bike has the the weave disease too.

have I tried.......YES ! I have tried everything. My easy solution is to not go 100+ mph .

Edit: OK one thing I haven't tried that Ive been thinking about.....I want to check the compression force on EACH fork with a scale to see if there is any difference. Im thinking a digital scale and a jack....or something.....

 

[posplayr]

It's good to hear that someone has the same issue !
I noticed that your bike is fitted with Ohlins shocks?
Are you able to adjust the compression and rebound damping separately?
Do you believe the issue is related to too much compression damping or too little rebound damping?
In the 80's the engineers used shocks with very little compression damping and harder springs that in turn required more rebound damping.
Not a good idea, compounded by the fact that the first "mag" wheels were massively heavy thus making it more difficult for the suspension to control all this unsprung mass !

I have a theory and it seems to be confirmed by other riders I have spoke to. With a high profile rear tire (relatively flexible sidewall), you can develop a weave in a sweeping curve when there are undulations in the road.

As you are going through the turn, and you go over an undulation when the rear compresses there is a tendency for the bike to lay over into the direction of the sweeping turn. Each undulation and another laydown. When the rear uncompresses the bike stands back up.

I attributed the compression to an increased rear tire sidewall flex causing the bike to weave. A stiffer rear spring and stiffer side walls made it go away. Of course this was in the course of doing an 88 Gixxer upgrade.

I don't think it really has anything to do with the damping. It only happened to me when I had the SU-143 Ohlins which did not have any adjust-ability but did have an under sprung spring for my weight and load. It was really noticeable with 100 lbs of camping weight on the rear.

I later got some SU-145's fully adjustable (the ones you see on the bike) and bumped up the spring stiffness as well.


Part of the discussion was here. After rereading I realize that part of the issue was overly stiff front and under stiff rear making it worse. It is really all about getting the sag correct both front and back.

http://www.thegsresources.com/_forum/showthread.php?t=140521&highlight=Ohlins+preload&page=2

 

[John Kat]

I like your theory about the flexibility of the rear tire !
Like you I have a modified GS 1000 with GSX R 1100 K wheels and suspension and NO problem at all in handling.
In fact, your theory could be validated if the rate of weave could be correlated with the speed at which the rear wheel rotates.
In other words if the weave happens once per second at a given speed the wheel should go round one full turn in the same period.
Given a diameter of 65 cm the bike travels about 2 meters every second in the above example or 72 KM/H.
In my experience the weave develops typically above 120 km/h meaning that the weave occurs faster than once per second?
Why not?

 

[posplayr]

I like your theory about the flexibility of the rear tire !
Like you I have a modified GS 1000 with GSX R 1100 K wheels and suspension and NO problem at all in handling.
In fact, your theory could be validated if the rate of weave could be correlated with the speed at which the rear wheel rotates.
In other words if the weave happens once per second at a given speed the wheel should go round one full turn in the same period.
Given a diameter of 65 cm the bike travels about 2 meters every second in the above example or 72 KM/H.
In my experience the weave develops typically above 120 km/h meaning that the weave occurs faster than once per second?
Why not?

It could be somewhat speed related but more to do with the natural frequency of the rear spring mass system. As I recall with that particular road undulation, the weave was closer to every 2 seconds and was stable but unsettling.

Basically the rear was squatting more than the front. On a straight there would be no weave. But since I was banked, it would cause the roll motion in the same direction as the turn and in direct synchronism with the rear compression. Nothing really to do with the wheel motion.

The only thing I could figure to couple with the rear compression was rear wheel slip angle when banked.

 

[John Kat]

I just came back from yet another test ride!
This time I went back to the OEM rear shocks of my GS 1000 ST.
The configuration is 100% stock except the rear swingarm from an 1100 Katana and the rear wheel from a GS 1100 with the corresponding disk and caliper.
This is a major breakthrough in roadholding!
The bike feels much more planted and the wobbles have almost disappeared.
As the speeds are rising it's important to avoid "hanging" on the bars to keep the bike steady but apart from that I believe that for a 30 year old bike it's pretty good.
My personal preference would be to have a somewhat larger handlebar to hold the bike in "the just in case" situation...
Why is the roadholding better now?
The OEM springs are softer than the Koni's rated at 100/185 lbs/inch.
This leads to both a little more trail for increased stability and a better use of the shock absorber's travel that in turn puts less disruption on the front end.
Here's a picture of the set-up

 

[Guest]

Damping

Damping

Seems they works better as the springs are softer, yes? Maybe the Konis didn't have enough rebound damping? So the spring extends too quickly. This causes a lot of weaving. My '83 1100 Katana would do that. I was only 21 and weighed 12olbs. Heavier frinds would ride it without problems. I upped the rebound to the third and that solved it. The bolt on fairing to the forks changes loads fed into the frame. My adventure with this was a large, red, semi-clear windshield mounted to the 750 forks on my '81 GS750 with a 1200 engine. Right at 120, it would go into a weave then as I tried to power through it, it turned into a wobble and a nasty tank slapper. Luckily, I held on tight as it really did try to throw me off. It even bounced back and forth accross two lanes one the freeway until I slowed down. I think this was the Los Angeles freeway? I think running from LA to Santa Monica. Later, I found some funny, black "strings" hanging from the V&H collector. Figure out what those were?
Anyway, the load change dramatically and if raising the front end allows the weaving to disappear, then maybe the head angle is too steep for the combination or the trail is not enough. Maybe you could experiment with teh triple clamps from a gS11 with leading axle forks. This would give more trail. These old pencil forks are rather flexy as well. Even the 41mm GSXR. I would watch them on my Katana and see the axle moving up and down very little but moving front to back up to an inch. Think of what the frame does?
Okay, probably no helps but a little "fun".
Laters
G

 

[posplayr]

did you ever measure your sag before and after the shock change? Was there a length change?

http://www.thegsresources.com/_forum/showpost.php?p=1198228&postcount=38

 

[John Kat]

did you ever measure your sag before and after the shock change? Was there a length change?

Yes, the OEM spring on the 2nd level of preload (as tested) gave :
No load: 325 mm
Bike only: 315 mm
Bike+rider: 300 mm

The Koni spring at minimum preload gave:
No load: 325 mm
Bike only: 323 mm
Bike+rider: 308 mm

Clearly the Koni has too much preload while the initial travel is the same for both with the rider ( 73 kg) on board.
The Koni gets much harder thereafter as it is progressive...

 

[posplayr]

Yes, the OEM spring on the 2nd level of preload (as tested) gave :
No load: 325 mm
Bike only: 315 mm
Bike+rider: 300 mm

The Koni spring at minimum preload gave:
No load: 325 mm
Bike only: 323 mm
Bike+rider: 308 mm

Clearly the Koni has too much preload while the initial travel is the same for both with the rider ( 73 kg) on board.
The Koni gets much harder thereafter as it is progressive...

You are apparently way to stiff in the rear with the Koni shocks.
How about the front?

I think this is about balance between front and back so they front and rear act in unison. Part of what contributed to mine was an excessively stiff front. Yours is perhaps the opposite but also giving you undesirable effects.

Ohlins suggests:

-------------F-------------R------
Static-----15-30--------10-20----mm
Laden-----35-50--------25-40----mm

Your Koni's are:

-------------F-------------R------
Static-------????----------2-----mm
Laden-------????----------17-----mm

Your OEM springs seem just at the stiff extreme side of the Ohlins recommended range.

-------------F-------------R------
Static-------????----------10-----mm
Laden-------????----------25-----mm

 

[John Kat]

Ohlins suggests:

-------------F-------------R------
Static-----15-30--------10-20----mm
Laden-----35-50--------25-40----mm

I measured the front aswell and the results are:

Static------43----------10------mm
Laden------66-----------25------mm

If I decrese the preload to minimum at the rear I get

Static------43----------13------mm
Laden------66-----------25------mm

Clearly there is not enough air in the front suspension and the rear spring rate is too high for my weight.
What's amazing is that Cycle magazine tested the GS 1000 in March 78 and Cook Neilson used the hardest preset value for the rear shocks on the track with very good results.
I suppose the springs were upgraded after this test?
As I have some original GS 1000 EC shocks I compared them to the original GS 1000 ST shocks.
The wire diameter is the same at 7.5mm but the S version has 13 turns while the EC has only 12 turns so clearly Suzuki had already decided to soften the springs on the S model!

 

[posplayr]

I measured the front aswell and the results are:

Static------43----------10------mm
Laden------66-----------25------mm

If I decrese the preload to minimum at the rear I get

Static------43----------13------mm
Laden------66-----------25------mm

Clearly there is not enough air in the front suspension and the rear spring rate is too high for my weight.
What's amazing is that Cycle magazine tested the GS 1000 in March 78 and Cook Neilson used the hardest preset value for the rear shocks on the track with very good results.
I suppose the springs were upgraded after this test?
As I have some original GS 1000 EC shocks I compared them to the original GS 1000 ST shocks.
The wire diameter is the same at 7.5mm but the S version has 13 turns while the EC has only 12 turns so clearly Suzuki had already decided to soften the springs on the S model!

I was wondering about the front springs ; maybe if you get some progressive springs for the front (to stiffin it up), and lay off the preload with your OE shocks you will get into the proper range.

The other way is to cut off about 3"-5" and add a spacer if you want to go cheap.

 

[Sandy]

I was wondering about the front springs ; maybe if you get some progressive springs for the front (to stiffin it up), and lay off the preload with your OE shocks you will get into the proper range.

The other way is to cut off about 3"-5" and add a spacer if you want to go cheap.

I've been following this for a bit to see where it's going and thought I'd jump in. My bike is a '79 GS1000N and at one time had a factory "S" fairing, brackets, mirrors, etc. '79 "S" was merely cosmetic so it should be equivalent to yours. Right now it hasn't got the fairing anymore (I broke it) but with or without it the handling didn't change. My setup is progressive springs up front w/no air and 15W fork oil and STOCK rear shocks set usually on the stiffest setting and damping set at max. I quite often push the handling capabities of my bike to the extreme and other than the occasional wobble or weave (a fork brace fixed some of that) it handles just fine. Maybe this can be used as a baseline to get yours sorted. I think as long is the stock shocks haven't developed any leaks they should work fine. The stock front springs are known to be downright awful though.