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

[John Kat]

I believe the R6 conventional right side up fork was 43mm but I didn't put my calipers on it. Very nice fork indeed, but 320mm rotors makes GS wheels require greater lengths to mount. Adapters on the 15mm offset Ducati rotors could be made and could even just re-drill the bolt pattern possibly, it's 80mm circle, shift it between the holes and drill ours 78mm circle. Adapter would just be a top hat spacer to locate it better on the bore than bolt-centric, & spaced out approximately 16.25 mm off hub approximately.

I did not measure the distance between the R6 caliper mounts, so I am not sure the clearance to wire spokes. With mag wheels I think you'd be good in vmx12 triples. Youll need to slightly mod steering stem to drop upper bearing surface several millimeters, or machine a gsxr/Busa aluminum stem to dimensions of vmx12 triple, use m14x1.0 top bolt instead of busa/gixxer alloy nut, remove retaining roll pin & press out vmx12 stem press in shorter aluminum busa/gixxer stem turned in lathe to dimensions of vmx12 stem diameters.

Of course, if you go your typical route, maybe you'd just get a fancy adapter made to run stock GS calipers? Going to these lengths, I'd definitely look into swapping to the twinpot calipers or just using the R6 and the Ducati rotors or custom ordering those EBC Racelite rotors but with steel floating rivet buttons not aluminum as they come. Don't get too spongy on master cylinder (bore to piston ratios) as you'll end up with immensely powerful brakes that you could lock up too easily in a panic scenario @ 320mm !

I need to absorb all this information but the plan is to use my GSXR 1100 K triples and just slide the R6 stanchions in them.
As for the front wheel I would be using the 18" GSXR 1100 H 3 spoke model.
The calipers are currently the GSXR 1100 2nd gen calipers.
This project is described here: http://www.thegsresources.com/_forum...ame&highlight=

[GSYOSHI]

I am looking into a local front end from a 2007 SV1000. Comes with brakes in good shape, he's asking 250(Can). Just waiting to hear back from the seller about length and offset. Found a length on a forum of 735mm. I am hoping to put Slabside GSXR 18" wheels on it and install risers for superbike bars. I think they are a pretty basic (not cartridge) fork but 43mm and dual disk. Any thoughts on these for a 78 GS750?

[Chuck78]

Why bother with all that work to retrofit if they are not cartridge????

[GSYOSHI]

Why bother with all that work to retrofit if they are not cartridge????

Sorry I should have put a question mark at the end of my statement that they weren't cartridge. These are the things I am trying to figure out. Anyway they are fully adjustable cartridge forks as far as I can tell from the internet. I found someone on another site that put SV650 forks on his Katana. Still digging stuff up. Anyway Seller said they are 736MM long and the offset is 36mm. Trying to get more info from the Kat swap.

[Chuck78]

36mm offset doesn't seem like anywhere near enough to run a slabside gixxer 18" front wheel, even if you raise the rear drastically, you'll still have a large amount of trail. Trail is what makes the steering stable, but too much and it will feel slow like a cruiser hardly davidson, not sporty and fun. Not much point to a swap of a sporty high tech front end to give it even more trail than stock, unless you don't ride it aggressively or have any twisty fun roads around. Stock forks with emulators, sonic springs, and 20mm-25mm longer upgraded $300-$450 rear shocks will make a nice sporty geometry and upgraded damping.
The SV1000 front on 18's will have much more sophisticated damping and better roadholding, but is not going to steer terribly well (slow).
1" taller rear ride height and a lower profile front like a 100/80-18 combined with a taller 140/80-18 rear or 150/70-18 (not as tall but taller than stock on most gs's) will get you closer to a sporting geometry. I'd speculate that'd get you back to stock GS trail specs but with the rake steepened by about 1.85 degrees.

Look at the SV1000 rake and trail, and SV1000 front tire outside diameter. Compare that to the GS spec.
Then figure that every 1" change in ride height changes the rake roughly 1 degree (raising the rear +++ combined with dropping front ---- , adding both numbers no negative/positive addition/subtraction)

That will give you an approximation of your trail . You can mock up your bike ride heights by dropping g the forks in the triples and shimming the rear tire up for simulation of taller rear and shorter front (use HALF the diameter of the tire spec as your shim height, the radius), then measure the head tube rake. Smartphone angle finders can be pretty helpful if calibrated.

Then you can use an online rake and trail calculator to plug in proposed front tire diameter, triple offset, and your measured rake simulation figure, and see where you are at with trail. 4" is good, 3.9" is a bit more sporting, 3.8" is great quick sporty steering, 3.75" is about the limit for a very sporty steering geometry before you start to compromise stability. On our old frames, it's bordering on getting twitchy there.

[GSYOSHI]

36mm offset doesn't seem like anywhere near enough to run a slabside gixxer 18" front wheel, even if you raise the rear drastically, you'll still have a large amount of trail."

Thanks allot for your reply. I have been following this thread for a while trying to figure out the best way to do this. Also John Kats posts... I have punched the numbers into rake and trail calculators that you have given here and I understand that I want just under 4" of trail to be an improvement. I have seen recommended and have been recommended myself the B12 forks but being less offset and longer than the SV1000's wouldn't they be even worse? I am getting no better than 4.4" trail with the SV's and so it would make sense that they are not what I am looking for but with the bandits I am getting 4.75" trail so if these are considered to be a working swap than either I am doing something wrong or they just are not a good option either. These are rough and dirty calculations of course but I want to get allot closer before I crunch down to fine numbers.

Thanks again. I was following the thread hopping a plug and play option would show it's head. I appreciate the work you have put into this. I am likely to just run what I have this summer and look into it further next winter. The sun is shinning and my bike is in pieces.

[Chuck78]

17" front wheel will cure it, or custom triples. I can point you to 2 affordable custom triple options.

[Chuck78]

I just got this crazy idea due to WERA vintage racing rules that I could swap GS1000 37mm dual disc fork lowers onto GS500E stanchions to have a GS dual disc fork under the 38mm max. fork diameter regulation for Formula 500 (building a 489cc GS425 to fit in that class).
Then I recalled how some Triumph Thruxton owners swap 41mm cbr600f3 fork stanchions/cartridges/etc into the triumph lowers...
Then I thought I could go as far as to swap these VTR1000F Superhawk stanchions and cartridges into some GS1100GK lowers... This would preserve the GS's 1970's classic appearance, & I could still run my salty_monk custom twinpot brake setup, & I wouldn't have to worry about adapting my GS hub to the big Honda axle (although it would be much stiffer), and no worries on the street about having to run a speedometer drive off of a 17" wheel bike (best solution I found so far was get custom gauge faces printed that have the speed markings corrected)

If this or even the cb600f3 (same as last year of F2) guts would swap into the 41mm GK sliders, that would be fantastic.
Then the only problem one would have is getting replacement bushings for the GK forks, as they are obsolete, & racetech does not list them in their catalog.
Lastly, I could make some custom 41mm triples with 194mm spacing or refer back to my notes to see if a late model nighthawk or VF1000F triple had that same width. Narrowing it would mean I could run the salty brake mod without any hub spacers.

[TiiMuch]

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.

[limeex2]

I used a 95-97 Triumph Sprint 900 front end. It bolted right up with only a upper bearing and a thicker washer on top of the bearing. Harder to find though, but I have one I use for spare parts after the motor went away. 97's are fully adjustable. They use above the triple clip-ons and have 3 different height bars, 4 with a spacer. The project is stalled for now due to summer riding season. I have a Bandit rear end I will be using. 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.

[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?