More modern cartridge fork options - retaining GS wheels & proper/revised geometry

[Chuck78]

Ok. Maybe got quite the treasure trove of restomod parts tonight.
Two 85-87 GSXR 18x3.5 rear wheels and one 85-87 18" front wheel.
And a 1989 1100 GSXR front end. Complete.
Is that angels I hear singing?!.

Ive got a Bandit rear end too.
Whats the smartest/simplest way to upgrade my 83 GS1100E suspension and especially the front brakes without losing the ground clearance for the 4-1 Supertrapp?.
And radial tires.

Wow... quite the score. The triples will give you a lot of trail if you run the 18" front wheel, but even with the 17" front wheel, due to the geometry of the GS1100E frame, you will have a good bit more trail than what is desirable.

I would measure the spacing on the gsxr1100k triples, and compare to the 2nd Gen vmax1200 tripkes. I believe I posted the width in this thread. They will get you exactly what you want in terms of ground clearance and sporty steering geometry. Your fork springs may still need upgraded with the 1100k front end mounted. It is possible though that you could do some calculations and chop a decent amount of coils out of the front fork springs to stiffen the rate, and find suitable tubing stock to shim the shorter spring afterwards.
I'd highly recommend sending the fork to Matt Wiley at Racetech to have him revalve it for you. It will totally transform that 2st gen cartridge system.

The gsxr1100k forks are 43mm, correct? I have read a slight bit of conflicting spec information on them. I will have a pair in the mail here shortly myself! The slightly taller height and older age (vintage racing regulations) swayed me
I won't need to offset my custom triples downward to fit the clipons on top of the upper triple with these.

If I were you, I'd keep the GS1100E swingarm and get a nice set of $500-900 rear shocks custom sprung and valve for you (Works, YSS, or the top of the line Gazi). I would not mess with a Bandit swingarm conversion when you have such a sweet swingarm as is.
If you do rip it off the bike, contact me, I'll buy it off of you!

 

[Chuck78]

With Chucks advice on this thread I am going to figure out how to use 14" ZRX shocks. Then I can swap shocks around with my ZRX as needed, and I have 3 nice sets.

Don't quote me on this, but I believe the ZRX piggyback shocks are the ones my friend was referring to when he told me that they are decent shocks but the springs are far too stiff for my applications.
The big ZRX models must be substantially heavier than my 480lb modded GS750 & the other 550/650 projects I have.
You can combat that very easily by changing the shock mounting position and angle. Laying the shocks down at more of an angle (gives longer travel also) or bringing the lower amount more forward if you use a bandit swingarm would do just that. Allows you to use a stiffer spring.

 

[TiiMuch]

Hey. Thanks for the great info and inspiration.
I've been thinking of which way to go with this.
I did some preliminary measuring this am and it looks like the 18" gsxr wheel will bolt right into the gsxr 1100K fork. Basically replacing the front wheel.
And yes. Thinking of now keeping the gs1100e swingarm and running the wider gsxr 18" wheel. Running radials and keeping as much ground clearance as possible.
Weird but with a little looking the right parts kind of fell into my lap. Locally even?!.

Wow... quite the score. The triples will give you a lot of trail if you run the 18" front wheel, but even with the 17" front wheel, due to the geometry of the GS1100E frame, you will have a good bit more trail than what is desirable.

I would measure the spacing on the gsxr1100k triples, and compare to the 2nd Gen vmax1200 tripkes. I believe I posted the width in this thread. They will get you exactly what you want in terms of ground clearance and sporty steering geometry. Your fork springs may still need upgraded with the 1100k front end mounted. It is possible though that you could do some calculations and chop a decent amount of coils out of the front fork springs to stiffen the rate, and find suitable tubing stock to shim the shorter spring afterwards.
I'd highly recommend sending the fork to Matt Wiley at Racetech to have him revalve it for you. It will totally transform that 2st gen cartridge system.

The gsxr1100k forks are 43mm, correct? I have read a slight bit of conflicting spec information on them. I will have a pair in the mail here shortly myself! The slightly taller height and older age (vintage racing regulations) swayed me
I won't need to offset my custom triples downward to fit the clipons on top of the upper triple with these.

If I were you, I'd keep the GS1100E swingarm and get a nice set of $500-900 rear shocks custom sprung and valve for you (Works, YSS, or the top of the line Gazi). I would not mess with a Bandit swingarm conversion when you have such a sweet swingarm as is.
If you do rip it off the bike, contact me, I'll buy it off of you!

 

[limeex2]

Sorry for the misquote Chuck. One of the perils of working midnights. lol. There was a previous thread of the handling benefits of a 14" shock. I thought it would be nice that 3 of my bikes had interchangeable shocks, but it may not be worth the trouble. I believe YSS has a very nice, very adjustable shock that in the end would be easier to deal with. Upper mounts on the ZRX are incorrect also.

 

[bobgroger]

Is there a list of more modern wheels that will work with 17" sportbike tires? Particularly ones with provisions for a speedo drive? My research is just starting, but I am leaning towards a Gen1 Bandit front, I believe that wheel has a speedo drive. I already have a RF900 lower triple and a Bandit swing arm. I don't want clip-ons so the Bandit upper triple makes the most sense. I don't totally understand the whole geometry thing yet but does this seem like a workable plan?

 

[Chuck78]

Yes, taller rear shocks will steepen the rake some and that itself will reduce the trail to a more appropriate level, but when selecting tires, go with something in a smaller height or outside diameter - search the good tire options for specs, as not all 120/70-17 or 110/80-17 tires are the same measured size! Smaller tire outside diameter also reduces trail. The RF triple is designed with the offset to get proper trail on a bike with the RF900 front tire diameter AND the rake of the RF900 frame (25 degrees?). A 27 degree rake GS frame will generate a lot more trail, so a taller rear tire and longer rear shock will slope the GS frame forward more than stock which will also reduce rake and trail. Don't try to nail down the rake and trail figures of the RF900R, it is a much more advanced frame, but try to get closer to the rake and trail.

Read an article on rake and trail and how tire radius and triple offset affects that.

25.5 to 26.5 degrees rake and 3.76 to 3.9" trail is a good fun sporty feeling steering for a vintage GS.

 

[Guest]

Is there a list of more modern wheels that will work with 17" sportbike tires? Particularly ones with provisions for a speedo drive?

Pretty much all 17" front wheels will be 3.0" or 3.5" wide. The 3.0" ones will happily run a 110 width radial and the 3.5" work best with 120 width fronts. I can't say on the speedo drive, but you can look at parts diagrams on Bike Bandit or Partzilla and see which models show a cable drive.


Mark

 

[TiiMuch]

Lots of good information here Chuck.
Thanks.
Ive got all my bike stuff moved to my new home and will be able to start some measuring and figuring.
You posted some good ideas about the 18" wheels. I have those. And the gsxrK1 fork setup.
Im going to likely run the stock gsxr fork/triples with the 18"wheel and fit the 18" gsxr wheel into the stock swingarm.
Someone is gonna get a helladeal on a brand new set of Metzler Sport Klassics.
Just to make it interesting I have managed to collect a complete"thundercat" r6 front end.
Ive broken down my rough barn find 1100E and want to eventually make a 17/17 bandit swingarm 1100 out of that.. So I will be test fitting the r6 forks in a bit.
I need a gs500 rear hub for the 18/18 bike me thinks

 

[TiiMuch]

This is a YZF600r front end.
When i did a preliminary and cursory check for bearing compatability on the All Balls site it seemed that the bearings are identical bike to bike.
So. With a bare frame to try. I slipped the front end on, and it looks really good.
While the Yamaha bottom triple has the steering stops and the GS1100 has its steering stops on the top triple clamp it looks like there may be a fluke compatability.
The top Yamaha triple clamp includes a stout cast housing that holds/protects the ignition cylinder.
It looks like that will interface almost perfectly with the two bolt mounts on top/lateral aspect the Suzuki's steering head.
This could be as close to plug and play as you can get.
Will update.

 

[TiiMuch]

First test fit.

 

[TiiMuch]

[ATTA

Picture taken looking up at the underside of the top triple. Shows the cast alum triple clamp ignition housing and Suzuki bolt bosses on the top/lateral aspect of the steering tube.
The top clamp is sitting at least 1.25" higher than it will be.

 

[Guest]

This is a YZF600r front end.

<snip>

This could be as close to plug and play as you can get.

What year YZF600? How long are the forks?


Mark

 

[TiiMuch]

I will measure and post tomorrow.
Ive got the complete GS1100 fork and can put them side by side.

 

[TiiMuch]

The "Thundercat" Yamaha YZF600r was made from 1996-2007

The measurements of the forks in that lineup go:
From left to right.
Centerline of axle to top of fork tube.

YZF600f=785mm
GS1100E=787mm
GSXS1100"K"=740mm

Im thinking my first restomod GS1100E is going to be riding on the Yamaha front end. Bandit out back.

 

[johnod]

I confirm that the Bandit 1200 phase 1 forks offer a far better damping than the fully adjustable GSXR 1100 K ( 1989) forks.
Beware that the disk spacing is slightly different between the GSXR 1100 K and the Bandit 1200!
On top as the Bandit forks are much longer they will fit on the 1100 Kat's.
Here with GSXR 1100 triples and clip-ons:

What is a phase 1 Bandit, what is the difference?

 

[bobgroger]

What is a phase 1 Bandit, what is the difference?

Gen 1 might be a better description, 97-00. They have different tube spacing than Gen 2, but the Gen 2 calipers and wheel fits. If you use a RF900R lower Triple Tree and a Bandit upper you can put regular handlebars on. THe upper needs a simple bushing, I used a .750X.625 bronze bushing drilled out a bit. You can also use a Gen 1 Speedo gear assy, with a Bandit cable it hooks up to the GS speedo. Here is a pic of my in-progress conversion on an '80 1100E:

 

[johnod]

Thanks, you lost me with the bushing.
What is the bushing for?

 

[bobgroger]

Thanks, you lost me with the bushing.
What is the bushing for?

If you use the RF900 lower and the Bandit upper triple there is a space between the stem and the upper triple that I felt should be filled to stiffen things up.

 

[johnod]

I see got it now, so the stem is from the RF900, not the Bandit.

 

[HiSPL]

Has anybody considered using the V-Strom front end and wheelset?

The 1000 has a cartridge fork design, uses a 3 spoke 19" wheel, and has handlebar risers and clamps. The matching rear wheel is a 17x4.5" rim like a bandit.

They make pilot sports that fit these rim sizes too. The adventure bike market has brought back some support for a 19" wheel.