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

[Chuck78]

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

So it seems the previously most popular front ends to swap onto our bigger GS's have been 93/94(?) GSXR1000 (mentions of using 88-ish gsxr1000 triples on some swaps?), and Bandit 1200 43mm forks (steering stem too long - needs swapped or 89-90 GSXR1100K triples used - see Jim aka posplayr's posts on parts vs rake&trail corrections).

Both of these forks are a proper height for our bikes, as far too many modern fork swaps just bolt up a modern front end with an All Balls conversion bearing set and call it good without any regards to bike geometry, and often end up with USD (upside-down) forks or even RSU (right side up) forks that drop the front end so low that any speed bump or driveway approach smashes their exhaust into the ground, or else they end up with a bike that steers very heavily or is very twitchy due to not evaluating the ride height, rake change, and their relationship with triple clamp yoke offset / front tire radius changes / resulting trail measurement. Sure, you get phenomenally better dampening and brakes, and can move the modern wheels over to the GS, but adapting the rear wheels will take at least some custom spacers, offset sprockets &/or 520/525 chains, brake mods, etc., and we're here to help each other out with info so that you are all armed with knowledge to build better geometry/handling to go with that awesome cartridge dampening & modern braking!

My goal here is to bring to attention the common disregard for proper rake and trail on a vintage bike upgrade/conversion, as well as share my findings on what I learn about the best cartridge fork swap candidates and issues regarding them.


More to come...




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EDIT - So if you don't make it through my ranting and rambling, here's my current conglomeration of opinionated info and research copied from below on conventional RSU cartridge fork options, will update this (Need some 93/94 GSXR1000 fork info):



Ultimate swap for slightly lower front, best dampening, fully adjustable, opposed piston 4/6 pots:
*CBR600F4/F4i forks and modded VMX12 93-05 or custom billet triples


Excellent dampening and close to stock ride height, 310mm brakes and 4/6 pots:
*Bandit 1200 43mm forks (no external dampening adjust, need longer shocks and slight drop in front height to get respectable stable trail with 34mm offset GSXR 89-90 triples or other similar triples as discussed by other members - Posplayr etc - see their thread for gen 1 vs gen 2 b12 fork details, different triple width I believe)(custom billet triples will make this a GREAT geometry upgrade/converson)(Suzuki models seem to run the calipers inwards more, need triples spaced 2.5+mm wider than Honda options if brake/spoke clearance issues)


41mm cartridge fork with external rebound and preload adjustment, near stock ride height, 4/6 pot brakes:
*Honda VTR1000F SuperHawk (Firestorm non-USA) 775mm tall forks, PERFECT with the scarce GS1100GK triples, may be able to adapt the stem on VTR-width late model 90's/00's CB750 Nighthawk triples, slightly clearance calipers inboard side for extra assurance), same possibility on 1984 Honda VF1000F Interceptor triples but they are 190 spacing, must adapt to CBR600F2/F3/VFR750 non-abs calipers - great swap if you go to that length) (dampening could use some mods on these or Racetech gold valve upgrade, same as most of the other forks here really to get dampening perfection) $325-$700 custom billet triples will solve all research/modding hassles!


41mm cartridge forks near stock ride height, much easier brake to wheel clearance with sliding 2 piston calipers:
*CBR600F2 41mm forks
*CBR600F3 41mm forks
*VFR750 41mm forks non-ABS '94-'97
same triple options as the VTR1000F Superhawk although the 1984 VF1000F Interceptor triple, IF the stem can be adapted, would be a great candidate, as well as the newer retro CB750 Nighthawk triples IF stem height can be adapted. $325-$700 custom billet triples will solve all research/modding hassles!


43mm cartridge forks external rebound/preload, A++ factory dampening, shorter than stock @727mm for GS550/650/400-425-450-500/GR650:
*94-97 RF900R 43mm forks in custom triples, 727mm tall - shortest you can run on a GS without offset triples.


43mm cartridge forks, fully adjustable rebound/compression/preload, shorter than stock longer than RF's @ 745mm:
*89-90 GSXR1100K forks and triples, 1"+ taller rear shocks as typical to help reduce rake and trail to an appropriate improved geometry
(These are a substantial upgrade to any GS, but Racetech says that the dampening is rather crude for a cartridge fork, but they can custom modify their parts to vastly improve the dampening for a reasonable labor charge)



So far that covers most of the models that I am aware of, with emphasis on RSU (conventional appearance) forks closer to 775mm height as to retain ground clearance.

 

[Chuck78]

My drive for adrenaline and thrills has me always seeking out viable mods to make the best corner carvers possible out of these classy vintage beasts.
My love for vintage classic standards of course has me always trying to run GS wire spoke wheels. Dan aka Salty_Monk popularized the use of 296mm Honda CBR/VFR/etc 6 bolt rotors as a bolt on kit using 2 simple adapters he sells for the rotor spacing and lower caliper attachment of Kawasaki Ninja 2 piston sliding calipers.
'93 CBR900RR rotors on gs forks with ninja/gs500 calipers:

I've made my own factory-appearing version of that (photo above, welded extra material to steel bracket to be a direct bolt on to GS forks, buddy machined aluminum top hat 5mm rotor spacers for me) and figured when going the extra mile beyond the massive upgrade of cartridge emulators, stiffer springs, and tarozzi fork brace (which all greatly improves GS stock forks to a very pleasing upgrade performance/comfort level), I would look into maintaining a proper, stock, and/or revised performance geometry using some of these 78mm bolt circle 6 bolt Honda rotors (they come in 296mm & 310mm diameter) and utilizing the Showa/Honda forks that many of these rotors are compatible with.

I'd read of Greg here in Columbus (OhioCafeRacers on here & DoTheTon.com, OhioCafeRacers.Com as well ) having great success running Honda VTR1000F Superhawk forks (Firestorm outside of the USA) on his Dunstall GS1000 restomod, as well as meeting Jim aka DiamondJ at AMA Vintage Motorcycle Days, who also is running Superhawk forks with great success. These are 775mm extended length approximately, right in the range of stock GS1000 forks, etc., and running 4 piston Nissin calipers with a big interchange list of better 4 and 6 piston Honda/GSXR Tokico & Nissin 62mm mounting pattern calipers.

Mine with gsxr1000 6 piston calipers on bench (the 4 pistons stock have clearance issues to wire spokes with 193mm width triples) and Rickman fender mocked up:



Nate B aka Blackhammer has also now utilized these VTR1000F forks on his beautiful GS1100/1150 build:

*I should note that running 17" rims, as Nate has in this beautiful wire spoke wheel build, combined with 1"-1/25" longer rear shocks, will make triple clamp selection far easier - as you can get a snappy quick steering 3.8-3.95" of trail using the modern bike triples... For those running 18" wire wheels or early GSXR wheels, I have been doing A LOT of research to help us all out, which will benefit those running GS 19" 90/90-19 front wheels as well but they will only be able to get slightly less than stock GS trail figures.

I planned to do an ultimate road racer/canyon carver build with an old neglected/repaired ex-race bike Rickman CR900 frame modded for GS1100E engine mounts... the spare upgraded 3.50x18 & 2.50x18 relaced/upgraded GS1000 spoke wheels I had instantly got a new home, and the Superhawk fork was slated for this. Well, I should've done my homework... the rare Rickman CR750/900/CRE's are elusive in finding much info on, but after asking another forum member to measure his, turns out they used 28.149"/715mm long Betor 38mm dual disc forks, which shoots down my stock GS length VTR1000F fork upgrade, and now the GS750 is going to get its fully built up 35mm GS650 dual disc forks swapped for Superhawk forks! The Rickman frames are built around a lazy 28 degree rake and forks are basically THE SHORTEST you can possibly run on an 18" wheel. makes my goal of a modern ~25 degrees of rake almost out of reach...

To be continued...

 

[Chuck78]

"The VTR1000 forks work nicely in terms of length on a GS1000. I used those forks with the stock calipers and a CBR600F2 wheel. Triples are CBR600 lower with a custom aluminum top clamp. In retrospect I could have probably bolted on a Bandit 600 triple clamp assembly"

-Jim aka DiamondJ's bike, superhawk forks/brakes.

(I might add that those CBR wheels DiamondJ used are perhaps the most appropriate looking modern mag wheels I have ever seen in terms of looking correct on a vintage bike retrofit. Great job... I dislike most futuristic looking mags swapped onto classic styled vintage bikes, but this one here is my top pick for modern wider 17" radial tire wheels by a longshot...)

OhioCafeRacers Greg's Dunstall GS1000 with VTR1000F Superhawk forks (mild rebuild thread on here, more info on dotheton.com or caferacers.net):

Superhawk owners complain about the stock springs and cartridge dampening, but there are a few homebrew mods to improve them. The cartridge kits available from Daugherty and Racetech fully transform them to the most compliant and awesome dampening available.

These vtr1000f forks are near stock GS1000 height with a useable steering stem length (a hair shorter that a GS750 8v stem) in a nice quality triple clamp yoke set, and the VTR1000F has externally adjustable preload and rebound, and 296mm rotor spec (many many honda floating rotors available that fit GS hubs) with a fairly universal 62mm spacing modern caliper mounting setup!

 

[Chuck78]

The Bandit 1200 forks are 775mm same as a GS1000 height. I looked up two of the older gsf1200 Bandit specs 95/96-2000, & they run dual 310mm rotors, so 2 years of CBR900RR 310mm 6 bolt 78mm bolt circle rotors (98-99???) can be run on GS hubs and spaced appropriately to work with those years of Bandit brakes. The Bandit rotors are 5 bolt, did not look up center diameter specs.

Bandit steering stems are too long and need a gs1100e stem pressed in place, or need machined down in height. 89 gsxr1000 k triples work with them, or one GSR member is running ghe lower triple clamp from an RF900R and the upper triple clamp from the Bandit 1200 with a very minor bit of fab work to get them working great. Other 80's gsxr triples may also work.


Aside from the early bandit 1200 forks, 94-97 vfr750, all vtr1000f superhawk/firestorms, and 93-94 gsxr1000 are the good right side up modern forks to swap onto vintage bikes if you care about ground clearance, geometry, and proper handling/suspension setup, they are the tallest of the options for modern fork conversions. Reading vfr750 forum threads about fork upgrades is a good way to dig up information on which modern forks are taller to fit our vintage bikes, since the vfr's run the same height range of forks...

 

[limeex2]

Chuck, thanks for opening another thread on this subject. Your last one got me thinking, and this is what I came up with. These are off a 95-97 Triumph Sprint. Back to back comparison looked same. Length a little longer to compensate for above upper clamp clip-ons. Bolted right up, only issue was steering stem nut came approx. 3mm short of being able to tighten properly. I will Check free length now that I have a spec. It looks like your rotor spacers are aluminium. Ok to use aluminium for salty monk application?

 

[Big Rich]

Chuck, allow me to throw in some more info to the mix regarding Bandit steering assemblies....

I tried going with an early model 1200 lower triple with 05 calipers.....come to find out the fork spacing is different between the generations of Bandits. So I bought a lower triple from a 1250 (same lower triple from 2001 to 2011), and upper clamp from an 01-05 Bandit 1200. As mentioned above the steering stem was way too long for my GR650. After a little research I found that a 98-06 Katana stem fit the Bandit upper and lower triple perfectly.

I don't have measurements handy (or maybe at all), sorry.

 

[Guest]

Appreciate the info, taking along for reference.

 

[Chuck78]

relocating from another thread (I hijacked!), will edit this in next few days:
...anyway, the VTR1000F Superhawk forks will now go on my GS750-920cc, and I discovered two great setups for that. The 1990's (& late 80's/early '00's?) CB750 Nighthawk used the same axle as the VTR1000F, and 41mm forks, and has (from my Photoshop approximations) the exact width of Superhawk triples and around a 45mm offset vs the meager VTR triple (i.e. shallow offset/way too much trail on the VTR's). We may have a winner here! I'm not sure at all on the steering stem height yet, but I'm going to assume it's in the ballparks.

Also the PC800 cruiser/tourer triples run a similar axle in the GS1100GK width that fits Superhawk forks, and has an approximately (i.e. Photoshop scale guesstimation) of 5mm offset, another great candidate, but requiring brakes spaced in further if the steering stem height works out great.

VF750 Magna triples give 4mm offset, look really cool (chromed lower, billet looking cast top, some with indicator lamps built in), but are about 215mm width - big rotor spacers needed but zero fuss on these or the pc800 with caliper to wire spoke wheel clearance. Magna axle also looks to be of same Showa style as the VTR axle, and matching width for the Magna triples.
84 vf1000f interceptor triples look to be 190mm (1.5mm less caliper to spoke clearance, may need even the 6 piston gsxr1000 calipers clearanced) but are 41mm and 48mm or so offset. The nighthawk triples will require 4 piston caliper clearancing (angle milling one edge) or 6 piston gsxr1000 01-02 calipers but will clear for sure.


https://www.rbracing-rsr.com/advchoppercalc.html (use 0 degree triple offset, we're not building a raked chopper)
(GS750 58.7 wheelbase 27? rake 4.21" trail ((2.17" offset stock? Reverse engineered that, garage is frigid!)) 26.1 diameter 3.25x19 tire 26.4 diameter 4.00x18 tire)
(Tire diameter specs: http://www.avonmoto.com/products/street-bias/roadrider - don't forget if changing sizes, use the **RADIUS(half of diameter)** not diameter to figure ride height changes via subtracting from fork length with the "new fork length" option - subtract more if you add longer rear shocks, 1" rise in rear (or 2" larger rear tire) = 1" drop in front = subtract 1" equivalent new fork length)
Smaller front tires (110/80-18, 100/90-19) will lower excessive trail figures. A 110/90-18 looks appropriate for our bikes in modded form, but gives more trail (if you're going for an aggressive modern 24.5? rake this may help)
Lots of ways to manipulate this basic program to get more number crunching abilities out of it as-is if you get your head deep into it.

As far as rake/trail are concerned, with around a stock rear tire diameter of 26.1" , and a 100/90-19 front at 25.5", stock 4.00x18 @ 26.4" or my 140/70/18 @ 26.2", triples slid down 40mm on fork stanchions to run clipons on top (mill off cb750 handlebar risers), and a 45mm or 46mm offset triple, we are arriving at approximately:
25.7? rake (27? stock)
4.17" trail (4.21" stock)
58.04" wheelbase (58.7 stock)

On a wide gs750/1000 engine, I'd say it'd be better to run the forks slid just the width of the clipons through the triples, and add more length to the rear shock or a 150/70-18 on a 3.5" rear rim to get back lost cornering count clearance. Longer gs1100e swingarm will reduce the rear ride height very slightly also, bear in mind.

 

[Chuck78]

relocating this info from another thread I was rambling on and on over not the author's bike, will edit in next few days:

Jacking up the shock length/dropping the front about 1.35" additional with those tire sizes will give you a modern sports touring bike rake/trail of:
24.5? Rake
3.85" Trail
57.47" wheelbase

this will really bring your vintage machine up to modern handling specs without ruining it's cornering ability with very short inappropriate USD forks.

Also - I've learned that CBR600F2 and CBR600F3 forks are 41mm and adjust rebound cartridge also, and in almost the same height! The CBR600F4 (& efi CBR600F4i) are similar height but 43mm.

Great pair on ebay now (F2's 1992???) with Ontario moto tech Billet 30mm offset triples that are worth $150 resale to a modern sport bike owner.
Brakes may be different calipers but all run 296mm rotors that we need for GS wheels.

So add to the GSXR & Bandit 1200 fork swaps these -
94-97 VFR750
VTR1000F Superhawk
CBR600F2/F3

Very pleased to discover all this...

some GSXR750 speedo drives look to work on our hubs via ebay photos but will read low (120/70-17 calibrated), but Im looking into other suzuki cruiser 20mm axle speedo drives or modifying a VF750 Magna or VT750 Shadow A.C.E. speedo drive to fit my hubs.

Custom axle spacers will need made for any of these (& larger 20mm i.d. bearings) or GS axle adapters custom made see John Kat's thread, I believe he made adapters to run GS axle in Bandit 1200 forks)

Nate, I'm going to move most of this info into a new thread when I get a minute, but got very excited after geeking out on the GS geometry numbers to realize I can likely use the nighthawk triples, vtr axle & unmodified Coerce VTR aftermarket fork brace with my setup. My Fox Factory Shox piggyback shocks are taller than stock, so I'm going to get an awesome geometry with clips flush on top of the triples or drag bars on stock nighthawk triples & triples slid down an inch or so.

The Rickman will get 310mm 98 CBR900RR rotors & 94-97 RF900R forks, but sourcing triples with 45-55mm offset in 43mm tubes is quite difficult, may resort to $325 in the best price on billet custom triples I could find (typically $500-750)

 

[Lorenzo]

Chuck, yours is an amazing work of research but, out of curiosity, since I think it will be my next mod, have you considered/tried cartdrige emulators?
Thanks

 

[Chuck78]

Running cartridge emulators very happily in my 35mm GS650 forks with a Tarozzi fork brace and chopped springs that are about .83kg/mm - this is a pretty great handling setup that compliments a good $300-400 set of rear shocks quite well. Im just geeking out to the max with my tinkering nature. I just can't stand to leave stuff "good enough," especially when trying to build the ultimate Rickman CR900 powered by a kickstart 894cc GS750 engine.

What emulators give you is ESSENTIAL - seperate high and low speed compression dampening circuits... anything less is incredibly archaic. cartridge forks are even more refined road handlers, or better yet, road holders in aggressive riding conditions. A properly tuned set with Racetech or similar treatment will really help keep the tire in contact with the pavement in mildly bumpy conditions, which is extremely critical in aggressive cornering.

On the flipside, I was still blowing away all my buddies when I was testing 7.5w fork oil since my seals were leaking and I needed anything in there just to keep lubricating and give it some dampening. Even though my front end was hopping through bumpy turns like a pogo stick. Good tires and good riding strategy/skills goes a long way. Fancier suspension just makes things more confident and smoother. Emulators are great.

 

[limeex2]

I have emulators in all my bikes. Our roads in Minnesota are JUNK and resemble a war zone. As Chuck mentioned,good tires and skills go a long way, but with emulators you can ride like that all day,with less drama and still be able to get off your bike. A common day ride for me is 250+ miles on fun roads which are not in good shape.

 

[blackhammer]

Great thread Chuck, i think it should be a keeper really.
I should mention that i am using GS1000GK triples with the 41mm VTR1000 forks, no need for bearing changes etc. Although it then means you have to have max offset discs as well as disc/wheel spacers made up and change wheel bearings if you choose to use standard GS wheels.

 

[Chuck78]

89-90 GSXR1100K 43mm fully adjustable cartridge forks

89-90 GSXR1100K 43mm fully adjustable cartridge forks

These would be the 17 inch wheel forks that come after the models with anti-dive devices but before the models that were all upside down forks, 2 years only. They are identifiable by the lack of anti-dive mechanisms and the presence of a casting knob below the caliper mounts with a compression adjuster screw, and top rebound adjuster screw inside of the spring preload adjuster.

A lot of the RSU cartridge forks we're all interested in upgrading to could really benefit from a Racetech upgrade to the valving. These slightly moreso... but if you're going to buy the Racetech stuff for whatever fork you get anyways, & a 1" drop in front with 1 degree steeper rake (or standard height for a GS550/650/etc ) is what you're after, the fact that these are 43mm fully adjustable cartridge forks is very very awesome...

If you don't mind a lot of trail, the stock triples are good, around 34mm offset, & will be plenty rideable with a stock 90/90-19 or 100/90-19 front, although an 80's 18" GS or GSXR front would help a lot with getting the quicker steering. 18" GSXR wheels in the 6 spoke gs1150 style with 2.75x18 front and 3.50 or 4.00x18 rear (& GS500 cush drive sprocket carrier to align closer to gs1100& earlier engines?) with 110/80-18 front tire and 150/70-18 rear tire (can run radials on these also!) Would make for a killer handling bike, especially with 1" taller rear shocks to help with ground clearance and getting the trail number to a stable but agile zone...

A VMX12 93-05 triple with 6mm or so of shim under the lower bearing & the upper bearing area filed down slightly lower may do the trick quite well also... I'm actually looking into machining an aluminum 98-03 Gsxr600 stem to swap into the vmax triple, as it's just the right height and alumimum is much easier to cut in a lathe vs Hardened steel.



I inquired with Racetech about not seeing any Gold Valve kits on their site for these 745mm tall 43mm tube 310mm brake fully adjustable rebound/compression/preload cartridge forks that look very similar to the newer ZRX1100 Forks with the compression adjustment below the brake mounts:

Subject: 1989-90 Suzuki GSXR1100 forks

Do you offer any Race Tech gold valve fork kits for the 1989-90 Suzuki GSXR1100 forks? In your product search, it says "RT Only." does this mean that you do not have any kits available for purchase, but RaceTech can perform a revalve but requires sending the fork to RaceTech?

Thank you for inquiring. Yes these forks 43mm forks use 23mm Cartridges & should be sent to Race Tech for revlaving service. I just setup one of these for an AHRMA Vintage Road Racer & it required a lot of parts shuffling. We have valves that work well but require some modifications & use of extra parts not included in the kits that would make end user install a confusing & difficult tech support issue. The stock valving is very crude & the rebound valving should be addressed when using stiffer spring rates as OEM setup will be overwhelmed otherwise. The Race Tech rebound Gold valve that is used here requires a custom piston band be used for fitment into the cartridge.

Best option is to send forks into us at RT, our labor charge is very reasonable: http://racetech.com/ProductSearch/2/Suzuki/GSX-R1100/1989-90

Send in fork service is turn key as the completed forks are returned ready to install on the motorcycle. Typical shop turnaround time is 10 days, please use the attached form when sending the forks in for service. We will contact you with details & to confirm what you wish upon inspection of the forks.

Thank you for choosing Race Tech!

Matthew Wiley
Race Tech Suspension
951-279-6655 RT ext# 108
mwiley@racetech.com

 

[Lorenzo]

To accomodate for different racing/riding conditions, wider triples holes, could be milled and eccentric bushes slotted in, in order to have two selection of offset/ trail;
I suppose rake could also be catered for.
#limeex2
Same driving averages and road condition over here.

 

[Lorenzo]

......... .

 

[Chuck78]

Alrighty well I've done some more sleuthing... I determined that unfortunately for my situation, the RF/Bandit forks have the brake mount bosses further inboard than the Honda's, so at 195mm triple spacing, the Hayabusa 85mm wide 6 pot Tokico calipers *just* rub the GS wheel's wire spokes mounted in the 93-05 VMX12 triples. Funny that the Honda VTR1000F Superhawk forks at 192mm or 193mm width with 85mm wide OEM-VTR1000 Nissin 4 pot calipers give 44.7mm space between the calipers, where as the 195 spaced VMX12/RF900-Bandit combo with 86mm wide Hayabusa Tokico 6 pots gives only 42.5mm between calipers... So the closer spaced VTR forks give 2.2mm more spoke/wheel clearance between calipers, which would allow use of the GSXR1000 01-02 6 pots with a skimming off the back inboard sides of the calipers set up angled in a milling machine, or even some very careful and precise hand filing for clearance.



The Superhawk triple has a good stem to run in the GS frame, but modern minimal offset requiring 17" wheel or a very short 18" with much taller GS rear shocks.

The real reason I bring this up is because of the other excellent 43mm cartridge candidate, the CBR600F4/F4i (F4i=fuel iinjection, different wheels/rotor i.d.). they are a bit shorter than the 775mm VTR1000 Superhawks, but are longer than the very cool 745mm 89-90 GSXR1100 43mm fully adjustable cartridge forks.
I may make it over to the Rice Paddy to measure a $300 set of theirs, but I think I read 772mm top of stachion to bottom of fork, minus 10mm half of axle diameter minus the material below the axle. (CHUCK - EDIT IN ACTUAL AXLE CENTER TO TOP MEASUREMENT HERE)

The CBR600F4/F4i forks would work awesome with 93-05 VMAX 1200 triples and 01-02 GSXR 6 pots or the even better maybe are the F4i 4 pots (less maintenance on 4 pistons)
The VMX12/F4-F4i swap I now consider to be the ultimate RSU conventional cartridge fork option for a GS550/650/750/850/1000/1100/1150 upgrade. AND the F4/F4i forks have the same adjustable compression clicker below the brake mounts as the 89-90 gsxr1100k and the ZRX...

After doing some more reading, it seems that not only the 94-97 VFR750 non-ABS forks, but also the CBR600F2 & CBR600F3 aparently use sliding 2 piston calipers, as I read discussion on 599 Hornet guys saying go the extra mile to swap to 43mm triples so they can run the F4/F4i forks/brakes so they can get 4 pot calipers... The sliding 2 pistons are still a SUBSTANTIAL upgrade over our 1970's technology calipers, and probably even an upgrade over the very popular salty_monk twinpot mod that I and hundreds of others on this forum love.

Also I have a smokin' $20 deal ebay 41mm Honda PC800 triple clamp set coming in the mail, and I think this stem will work on the GS, has 204mm width, approximately 53-55mm of offset which will get a GS a really good trail number with a tall front tire (110/80-18 on 86 GSXR front wheel or 2.50 aftermarket rim, or stock 19" wheels). This with the VTR1000 Superhawk forks will likely make an AWESOME cartridge fork conversion without altering the geometry much at all from stock. I'd still go 3/4"-1" longer on the rear shocks over stock to get down to as low as 3.75" trail but after careful calculations, but would settle for 3.85"-3.95" trail for a long hauler bike. That's where the ebay Ohlins ride height adjusters or the YSS Shocks' +10mm ride height adjuster (that they ship with every set of shocks) comes in handy. Order shocks a good length to get 3.85"-3.95" trail, when you want a spirited ride in the twisties, add the extra length or crank up the Ohlins adjusters, and get the trail down for that extra quick steering response for the tight twisty backroads!

I still need to revisit the 84 VF1000F Interceptor triples, and the late model 90's/00's CB750 retro model triples, as both are 41mm and 193-194mm width, so they would work awesome in a GS frame with VTR1000F/CBR600F2-F3/VFR750-94-97-non-abs forks IF the welded in steering stem were adaptable.

As with the 93-05 VMX12 (VMAX 1200) triples, these are slightly too tall on the steerer for the GS, but a very thick and lightweight aluminum Hayabusa or late 90's/2000's GSXR steering stem pressed out of their triples (the ones that are 7.125" bearing surface total height, aluminum, tapered down in the middle, and run the same 30mm i.d. bearing top and bottom) can very easily be turned down in a lathe to swap into the VMX12 triples with converting to a top 15mm fine thread bolt thread vs the original VMAX top nut, shave the top of the stem off and tap the inside for threads, machine down o.d. of bottom press fit and match the o.d. and profile of the VMX12 triple on the top), or swap this modifiable GSX1300R/GSXR aluminum stem into any other aluminum lower triple candidate for that matter.
I determined that with running taller 775mm or so Bandit 1200 / F4i forks on the VMX12 triples, one could easily get one or two of the thick shims that AllBalls gives with some bearing conversions, and shim the lower bearing up to be maybe 6mm higher (still plenty of machined bearing surface above), and machine or even just hand file the upper bearing's lower bearing surface boundary area a few millimeters lower, and then successfully run the VMX12 triples in a GS frame with no stem swap at all.
The only down side here is that these 2nd gen VMAX 1200 triples are not as common on ebay. Salvage yards can probably scour their parts locator network and find some. They are a fine looking piece, aluminum uppers and lowers.

 

[Chuck78]

So if you don't make it through that ranting and rambling, here's conventional RSU cartridge fork breakdown:

Ultimate swap for slightly lower front, best dampening, fully adjustable rebound&compression, opposed piston 4/6 pots:
*CBR600F4/F4i 43mm forks 755mm height and modded VMX12 93-05 50mm offset or custom billet triples


Excellent dampening and stock ride height, 310mm brakes and 4/6 pots, 775mm length:
*Bandit 1200 43mm forks (no external dampening adjust, need longer shocks and slight drop in front height to get respectable stable trail with 34mm offset GSXR 89-90 triples or other similar triples as discussed by other members - Posplayr etc - see their thread for gen 1 vs gen 2 b12 fork details, different triple width I believe)(custom billet triples will make this a GREAT geometry upgrade/converson)(Suzuki models seem to run the calipers inwards more, need triples spaced 2.5+mm wider than Honda options if brake/spoke clearance issues)


41mm cartridge fork with external rebound and preload adjustment, near stock ride height, 4/6 pot brakes:
*Honda VTR1000F SuperHawk (Firestorm non-USA) 775mm tall forks, PERFECT with the scarce GS1100GK triples, may be able to adapt the stem on VTR-width late model 90's/00's CB750 Nighthawk triples, but likely need to lightly clearance (angle mill)calipers inboard side for extra assurance), same possibility on 1984 Honda VF1000F Interceptor triples but they are 190 spacing, must adapt to CBR600F2/F3/VFR750 non-abs calipers - great swap if you go to that length) (dampening could use some mods on these or Racetech gold valve upgrade, same as most of the other forks here really to get dampening perfection) $325-$700 slightly wider custom billet triples will solve all research/modding hassles.
Honda PC800 triples arrived in the mail, these are very similar to the GS1100GK triples, 55mm offset 204mm width and offset down so you can mill off bar risers & run clipons on top of the triples withour compromising ride height ground clearance in corners. Great trail number with a tall 110/90-18 & minimal rear ride height increase with these 55mm offset pc800's, could be the biggest winner for geometry & cheap availability running the VTR1000F Superhawk forks & 599 Hornet spec rotors (or non-USA CB400SF Super Four, all have greater 23mm offset in 296mm diameter).


41mm cartridge forks near stock ride height, much easier brake to wheel clearance with sliding 2 piston calipers:
*CBR600F2 41mm forks
*CBR600F3 41mm forks
*VFR750 41mm forks non-ABS '94-'97
same triple options as the VTR1000F Superhawk although the 1984 VF1000F Interceptor triple, IF the stem can be adapted, would be a great candidate, as well as the newer retro CB750 Nighthawk triples IF stem height can be adapted. $325-$700 custom billet triples will solve all research/modding hassles


43mm cartridge forks external rebound/preload, A++ factory dampening, shorter than stock @727mm for GS550/650/400-425-450-500/GR650:
*94-97 RF900R 43mm forks in custom triples, 727mm tall - shortest you can run on a GS without offset triples.


43mm cartridge forks, fully adjustable rebound/compression/preload, shorter than stock longer than RF's @ 745mm:
*89-90 GSXR1100K forks and triples, 1"+ taller rear shocks as typical to help reduce rake and trail to an appropriate improved geometry
(These are a substantial upgrade to any GS, but Racetech says that the dampening is rather crude for a cartridge fork, but they can custom modify their parts to vastly improve the dampening for a reasonable labor charge)



So far that covers most of the models that I am aware of, with emphasis on RSU (conventional appearance) forks closer to 775mm height as to retain ground clearance.


I have also read multiple mentions that the Bandit 1200 and RF900 forks, as well as the CBR600F4/F4i forks are really just about the ultimate RSU fork swap because their stock factory dampening is superior to most counterparts & has a very high level of tunability, and they have 4 pot/6 pot caliper compatibility with mounting configurations used on many highly regarded models for lots of caliper swap options. The Suzuki and Honda run similar calipers in Nissin and Tokico, but the Honda's (vtr1000, f4, etc) run a closer 62mm mount spacing with the lower mount sticking much further out behind the fork legs, Bandit GSF1100 & RF900R run 100mm caliper mounting with both mounts same distance right off the fork lower.
The RF900R / GSF1200 forks run the calipers more inboard on the forks, where the Honda F4/VTR1000F run the calipers more outboard with the rotors nearly touching the forks. So on the same width triples, the RF900R/GSF1200 forks will put the calipers several millimeters closer to the wheel spokes, where the Honda brake mounts put the calipers further away from the wheel spokes.

In the RF900R /GSF1200 Bandit fork brake options, the aftermarket $$$ Shindy Nissin 6 pot calipers give 3mm additional brake clearance @ 80mm width vs 86mm on the Tokico OEM Hayabusa 6 pots (& the VTR1000F/CBR600F4/F4i brakes & the 6 pot GSXR1000K2 01-02) calipers.







I have also read multiple mentions that the Bandit 1200 and RF900 forks, as well as the CBR600F4/F4i forks are really just about the ultimate RSU fork swap because their stock factory dampening is superior to most counterparts, and they have 4 pot/6 pot caliper compatibility with mounting configurations used on many highly regarded models for lots of caliper swap options. The Suzuki and Honda run similar calipers in Nissin and Tokico, but the Honda's run a closer mounting spacing with the lower mount sticking much further out behind the fork leg.

I was also checking out some ZRX1100 & ZRX1100 RSU forks which were a great height (765mm? Have to look up my notes), have adjustable preload, rebound,&compression, & run the same 6 pot Tokico's as the first 10 years or so of Hayabusa, & for 310mm rotors (98-99 CBR900RR rotors are a shoe-in for bolting to GS hubs!!!). These were VERY NICE RSU fork swap candidates!
Yamaha R6 RSU forks were the lightest I've had my hands on, 4lbs lighter than the cbr600f4i w/vmax 1200 43mm triples w/steel stem, 6 lbs lighter than the zrx1100 forks with a very long steel stem. R6 had alloy stem like the gsxr/Busa stem I'm using. I've also seen a crashed R6 fork split in two almost it creased so hard, the upper fork tubes are MUCH thinner than my GS750's... The R6 runs an excessive 320mm rotor, no easy bolt ons for a GS 6 bolt 78mm pcd hub. 296mm is plenty, 310mm duals is ALOTTA BRAKE, 320mm probably needs ABS to not tuck the front!

 

[Chuck78]

To accomodate for different racing/riding conditions, wider triples holes, could be milled and eccentric bushes slotted in, in order to have two selection of offset/ trail;
I suppose rake could also be catered for.
#limeex2
Same driving averages and road condition over here.

A few companies make billet triples with adjustable offset through interchangeable stem insert pieces. I have been roughly designing custom triples with a slight step down on top to fit clipons better without the forks dropped too much. When it came to rake and trail, I strapped the CR900 frame from the rafters and adjusted it for tire size choices specifically hand picked (from the 3 brands of very grippy tires I prefer) for fitment on rim & diameters to fit with my elevated rake. Then raised the rear to achieve near the maximum swingarm angle recommended. Measured rake of frame in this 380 mm shock/minimum fork height/ BT45V 110/80-18&140/80-18 simulated ride height. Came up with 25.6 degrees rake and only 4 degrees forward down slope on the seat rails, not bad! Then figured 49mm offset triples for 3.78"/96mm of rake. 95mm is a great quick steering but stable enough figure for racers. 96mm-100mm comes on most modern sport bikes. I figured with the shocks in their full +10mm extended length mode and the shocks mounted on the forward swingarm shock mounts for +8mm ride height, I was pretty good to go. Designed with rear ride height maxed out and the least trail I thought was acceptably stable but quick steering, then I have the ability to increase rake and trail for longer hauls just by moving the shocks to the rear mounts. Brilliant, Rickman 2 position lower shock mounts and YSS Suspension +10mm ride height adjusters on all their nice alloy body models.

 

[Chuck78]

The PC800 triples & axle are a total winner for the VTR1000F Superhawk forks on a GS750/850/1000/1100!!!!

^^^
A mere 1/16" shorter total bearing height top to bottom versus a gr650 tempter stem that I believe is identical to my GS stem heights... no prob at all, looks like a great fit with only steering stop alterations needed.

Both triples are offset inward toward each other, which means you could really raise them up even higher to get the 800 mm length of some of the GS katanas that have been compared in other forks swap threads. or you could mill off the handlebar riser mounts and have more than enough room for the tallest of clip ons on top of the triples, then just add rear shocks in 10 mm or 20 mm over stock to decrease your rake and trail.


this will of course take a 17 inch wheel RF900R/etc speedometer drive, and custom front wheel spacers, or just a collection of super hawk and pc800 spacers cut down to the width needed.
no other leads yet on 18 inch wheel Cruiser speedometer drives that will work for better accuracy on an 18 or 19 inch gs wheel - custom corrected speedo face vinyl graphics or electric speedometer are options, especially for 19" wheels. 110/80-18 won't be incredibly off like a 19 will. Or look into gutting the speedo drive and swapping parts from a GS? Or just adapt an early 18" wheel GSXR speedo drive to it, or a late model mechanical speedo 20mm axle Suzuki v twin cruiser drive

PC800 stem uses same lower bearing size @30mm, and 26 mm upper vs 25 mm on the gs and gr stems. No problem getting bearings to fit.

204mm or so width gives a whopping 57mm clearance between the massively huge and powerful opposed 4-piston and 6 piston calipers. Plenty enough to clear wire spoke wheels and mags alike... more details and geometry estimations later.