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

[John Kat]

John, did you have any drawings that you had posted previously for those 15 mm to 20 mm axle adapters?

Did you ever figure out why the first GSXR 1100 K Fork was so stiff? You said you swap the fork tubes. I wasn't sure if you just meant the Chrome upper tubes, or the entire fork leg assemblies. You also mentioned some different oil viscosities. Have you just put too stiff of oil into it? 2.5 weight was best? In Bel-Ray?
How did the GSXR 1100 K Forks compared to the Bandit damping?

Those two forks get the vote for me because they look almost exactly like a GS Fork, whereas they very awesome performing CBR 600 F4 Fork has the modern style caliper mounts with the lower projecting rearward an inch-and-a-half further. This is probably not a big deal at all, but I like the fact that the first two that I mentioned look very much like a GS Fork.

Thanks!

Chuck

Chuck, you will find in attachment the spindle adapter required to fit a 15 mm spindle in a GSXR/Bandit front fork.
Please triple check all measurements as this is not the document I gave to the machinist...
Any further questions are welcome!
As for the GSXR forks I believe I used BelRay 2.5 W but I need to check my notes.
Remember that the Japanese discovered compression damping with the cartridge type forks.
In that respect the Bandit forks are a better choice from a comfort standpoint but you need to consider the fact that they are longer than the GSXR's that are adjustable.
The world is not perfect!
To me the ideal 18" wheels are those from the 1st gen GSXR.
They are very light and fit on the 15 mm spindle for the front.
Difficult to find overhere BTW!

PS: I can't load the PDF file so please send me your email
No don't worry, I'll take a picture later on!

[John Kat]

Here's the spindle adapter.
The recommended 15 mm spindle is the one from the early 1986 GSXR 1100 (model G).
Beware it moved to 17 mm the following year!

IMG_1151.JPG

[Chuck78]

Thanks John, I emailed you from my Yahoo address.
And then afterwards, I looked at the rest of this thread and saw that you posted a photo of your sketch! Is that what you gave the Machinist?

[John Kat]

Thanks John, I emailed you from my Yahoo address.
And then afterwards, I looked at the rest of this thread and saw that you posted a photo of your sketch! Is that what you gave the Machinist?

It was a long time ago and I believe that minute changes were made while discussing with the machinist.
You need to examine very carefully the length of the threads both internal and external to ensure the engagement will be made fully.

[John Kat]

I measured the OEM triples coming from my GS 1100 Katana and I can confirm that the Vstrom triples should fit.
It's a bit confusing as the landings are closer on the Katana stem but the bearings are well 151 mm apart.
The Katana P/N fiche mention a 30x40x1.5 mm spacer below the lower bearing.
I believe two would be needed to raise the lower bearing as high as possible.
A question: does the lower bearing come with it's dust seal?

[limeex2]

Yes Chuck that is a GS1000. Had to cut off the steering stops to make it fit. Its my basement test mule. It will have that front end. Bandit swinger. Using ZRX1200 shocks with upgraded internals. I will need help/recomendations on rear shock placement to get frame geometry into modern standards.

I'm trying to go after this look. I have a built 4v 1166 or fresh, strong "stock" 4v 1100 to use.

https://www.pinterest.com/pin/831688256158082119/

This is a 2nd option as I am doing 2 bikes. It would need to have street ergos but you get the idea.

https://i.pinimg.com/originals/37/7e...6ec4929c43.jpg

[Chuck78]

They both look great! The first picture made me realize that maybe it was just the silver that put the futuristic looking body work on those katanas over-the-top for me, that one looks a lot more appealing in red and white.

Second one I like A LOT! The open triangle on a functional bike (i.e. non-hipster art project/1st attempt at welding & sawzall use) caught me off-guard though, it looks very out of place without side covers or number plates on it! On a functional true race bike!

[John Kat]

Just to confirm that the DL 1000 triples should fit the GS 1000 frames.
The bottom bearing is now in place on the DL 1000 Vstrom triple and when positionned on my GSXR 1100 G/H frame, the top bearing landing (on the stem) protudes the seat of the bearing (on the frame) by 4 mm.
Next come the lock stops but I will open a new thread to discuss this.
Here's a picture:

IMG_1183.jpg

[Chuck78]

Revisiting this for some of my upcoming project bikes...
I now have a round column Vertical Mill, Enco 29, similar to the RF 30 and RF31 newer models, & a rotary turntable, adjustable boring head, etc for it...
I am looking at buying some 4 or 4.5" x 2.5" thick 6061 T651 aluminum bar stock & custom milling my own offset upper triple to make some of these shorter modern forks come back up to stock GS ride height by dropping the upper clamping portions of the fork tubes about 35mm offset lower.
this would allow me to run the GSXR 1100 K 1989 forks at stock ride height. it turns out that the comparison measurements for our bikes are a bit skewed because the GS upper triples already offset down a little bit, and are approximately 3/4" advantage increasing in ride height over a flat upper triple.
so just measuring the fork length from the center of axle to the top of the chrome tubes is not enough, you also need to take into consideration the steering stem length, upper triple placement, and any offset to drop the outside of the upper triple lower than the center of it...

This places a bit more stringent criteria on fork heights.

so my only serious motorcycle twisty road week long road mountains trip of the year, I was scraping left and right when fully loaded with camping gear and going through really tight twisties for a week. A little bit stiffer fork springs would help, but I already have longer rear shocks...

So now I have become very adamant about running the proper ride height on the front of a GS 750, GS1000, GS 1100, or the bigger shaft drive bikes as well if you are into those.

I will say that I think the VTR1000F with either the PC800 triples, or if the 90s and 2000 CB750 nighthawk triples or the 84 Honda VFR interceptor triples would work (steering stem height for bearing spacing is unknown) those might be the best ticket for adjustable (rebound) damping. The Bandit 1200 forks are still at the top of the list, especially considering you can run the V-Strom triples. Taller rear shocks and an 18 inch front wheel would make that set up work very ideally.

I never really looked into the suggestion of the 97-07 YZF600R Thundercat forks, but it seems that any modern sport bike that is designed to run clip-on bars on top of the triple clamps, they are going to be the taller forks that we would need. When searching for conventional forks. Or inverted forks I suppose as well.

Those YZF600R forks are 41mm, so I dont have a definite recommendation on triples other than the rare GS1100GK triples (50mm standard GS offset) or Honda PC800 triples (55mm offset, only for taller tires like stock 19" or 110/90-18), or possibly investigating 90's-2000's CB750 Nighthawk triples for steering stem height compatibility.

The great thing about them is the height, and that they have fully adjustable compression and rebound and preload, all externally! That bike is a bit lighter though (412lbs dry, 463lbs wet), so they will be a bit soft for a heavier GS and a very expensive set of fork springs would be needed, or else chop those stock fork springs slightly. They are 0.81 kg/mm. For a GS550 or 650, these would be pretty incredible as is with the right triples (GS1100GK!).

The 99-07 versions are listed separately by Racetech, although 97-98 are pretty similar. The first 2 years (95-96) are drastically different and do not look appropriate for a vintage bike

[John Kat]

Revisiting this for some of my upcoming project bikes...
I now have a round column Vertical Mill, Enco 29, similar to the RF 30 and RF31 newer models, & a rotary turntable, adjustable boring head, etc for it...
I am looking at buying some 4 or 4.5" x 2.5" thick 6061 T651 aluminum bar stock & custom milling my own offset upper triple to make some of these shorter modern forks come back up to stock GS ride height by dropping the upper clamping portions of the fork tubes about 35mm offset lower.
this would allow me to run the GSXR 1100 K 1989 forks at stock ride height. it turns out that the comparison measurements for our bikes are a bit skewed because the GS upper triples already offset down a little bit, and are approximately 3/4" advantage increasing in ride height over a flat upper triple.
so just measuring the fork length from the center of axle to the top of the chrome tubes is not enough, you also need to take into consideration the steering stem length, upper triple placement, and any offset to drop the outside of the upper triple lower than the center of it...

This places a bit more stringent criteria on fork heights.

so my only serious motorcycle twisty road week long road mountains trip of the year, I was scraping left and right when fully loaded with camping gear and going through really tight twisties for a week. A little bit stiffer fork springs would help, but I already have longer rear shocks...

So now I have become very adamant about running the proper ride height on the front of a GS 750, GS1000, GS 1100, or the bigger shaft drive bikes as well if you are into those.

I will say that I think the VTR1000F with either the PC800 triples, or if the 90s and 2000 CB750 nighthawk triples or the 84 Honda VFR interceptor triples would work (steering stem height for bearing spacing is unknown) those might be the best ticket for adjustable (rebound) damping. The Bandit 1200 forks are still at the top of the list, especially considering you can run the V-Strom triples. Taller rear shocks and an 18 inch front wheel would make that set up work very ideally.

I never really looked into the suggestion of the 97-07 YZF600R Thundercat forks, but it seems that any modern sport bike that is designed to run clip-on bars on top of the triple clamps, they are going to be the taller forks that we would need. When searching for conventional forks. Or inverted forks I suppose as well.

Those YZF600R forks are 41mm, so I dont have a definite recommendation on triples other than the rare GS1100GK triples (50mm standard GS offset) or Honda PC800 triples (55mm offset, only for taller tires like stock 19" or 110/90-18), or possibly investigating 90's-2000's CB750 Nighthawk triples for steering stem height compatibility.

The great thing about them is the height, and that they have fully adjustable compression and rebound and preload, all externally! That bike is a bit lighter though (412lbs dry, 463lbs wet), so they will be a bit soft for a heavier GS and a very expensive set of fork springs would be needed, or else chop those stock fork springs slightly. They are 0.81 kg/mm. For a GS550 or 650, these would be pretty incredible as is with the right triples (GS1100GK!).

The 99-07 versions are listed separately by Racetech, although 97-98 are pretty similar. The first 2 years (95-96) are drastically different and do not look appropriate for a vintage bike

My personal conclusion for GS 1000 and GS 1100 Katana is to use a first gen R6 RSU fork for the GS and Bandit 1200 stanchions with DL 1000 triples for the Katana.
Here's a pictures of the GS 1000 so equipped.
The GSXR 1100 engine further helps for ground clearance of course...

IMG_1231 (2).jpg

[Chuck78]

My personal conclusion for GS 1000 and GS 1100 Katana is to use a first gen R6 RSU fork for the GS and Bandit 1200 stanchions with DL 1000 triples for the Katana.
Here's a pictures of the GS 1000 so equipped.
The GSXR 1100 engine further helps for ground clearance of course...

[ATTACH=CONFIG]59676[/ATTACH]

I have the privilege of checking out some of the Yamaha R6 RSU 43mm forks in person at the local Japanese bike salvage yard when I was investigating fork options, and I determined quickly that they were the lightest of all of the fork offerings I was looking at. Very impressive! I very high performance machine, the R6 is... THEN at the same wreckers, I saw an R6 front end that was in a bad front end collision, and I got to see firsthand how flimsy the thin walled fork tubes were, as they had folded over and creased and cracked as if you were crushing an aluminum beverage can... not a pretty sight how weak they were in a collision. I hit a deer at 70mph head-on and my 35mm GS forks were only bent something like .028" end to end, measured in the center at the fork bushing location! My wife crashed a 35mm set of forks at a 55mph rear ending collision into a car doing maybe 15-20mph, and her forks (BIG HEAVY OBESE HARLEY DAVIDSON FXR ROAD PIG) were only bent about 1/2". These R6 forks were flimsy and absolutely crushed and creased from this particular crash, and I got to witness firsthand how thin the walls of the tubing was as it was torn at the creasing.

Due to that, I skipped on those. I also passed on the Kawasaki ZRX fully adjustable compression/rebound forks, despite them being really nice and tall (those ZRX1100/1200's are really tall bikes), because those were the HEAVIEST of all the forks that I was looking at...

So for our GS's, I honestly think these are the best two easy cartridge fork swaps, especially if staying with an 18" or 19" wheel:

**VSTROM DL1000 43mm fork triples (____ - 2013, 1000cc, 42mm offset - better with 18" wheel or 17" and taller front ride height, but slow steering with 19" front)
**Suzuki Bandit 1200 43mm forks

or

**GS1100GK 41mm triples (50mm offset) (can substitute more common Honda PC800 triples with 55mm offset if you are running 19" wheel or 110/90-18 tire) (Haven't measured a 1990's/2000's CB750 Nighthawl steering stem, may be work-able with spacers under bottom bearing)
**Yamaha YZF600-R 41mm forks 1997-2007


The GS1100GK triples are getting harder to find nowadays, but the are the obvious shoe-in candidate with those YZF forks if you can find some GK triples. The GK wider axle helps also if adapting GS or 18" GSXR wheels to the modern 20mm axle forks. The GSXR 18's can probably more easily take a 20mm i.d. bearing to run the fork's stock 20mm axle, but 20mm I.D. bearings for GS hub bearing O.D. are VERY SCARCE. I think I bought up the last 2 that I had ever seen on the internet a few years back...

Those are the best two combinations I can come up with. The CBR600F4 and CBR600F4i forks are also really really nice fully adjustable forks as well. I have a set here for one of my project bikes that I got off ebay for $30+$26 shipping! Too cheap to not buy! Not as retro looking with the Honda typical brake mounts, vs the Suzuki and Yamaha forks having more GS-appearing brake caliper mounts, but excellent forks regardless.


The 43mm RSU forks at those V-STROM triples really are the best easy option, and the Bandit 1200 forks in my opinion are the ticket as they have a stiffer spring rate than most, basically a nice semi-sporty but still comfortable spring rate of around 0.74kg/mm. The 1989 GSXR1100K fully adjustable forks are the stiffest of any of these springs that I've looked into have not checked ZRX or R6 spring rates on Racetech application guides), at 0.80kg/mm. That's good for a light rider, aggressive riding, on a 465lb bike. A GS750 or GS1000 8v can be put on a diet to those weight figures with mods. Otherwise if you want a firm sporty ride, you're going to have to shell out some big bucks for aftermarket springs.

[Chuck78]

I believe I have the early Vstrom triples with removable handlebar fittings.
The bearing areas are both 30 mm in diameter as you stated however the bottom is slightly larger requiring a force fitting.
The bottom landing is 22.5 mm long while the top is 16 mm long.
The inner distance between the two landings is 151 mm.
Here's a picture:

[ATTACH=CONFIG]56368[/ATTACH]

John Kat
Revisiting this thread again, I think I might have solved two problems simultaneously!

Do you still have that VStrom DL1000 steering stem?
I was wondering if you could measure the press area of the bottom, from the step transitioning from the bearing seat area into the triple clamp press fit area, all the way down to the bottom.

I'm pretty certain that a GSXR or Hayabusa steering stem swapped into the V-Strom DL1000 triples would then make it the exact height needed for a GS frame.

From those measurements, what you gave totals 189.5 mm which I'm assuming you meant from the very bottom of the lower bearing area of the stem to the very top of the upper bearing area of the stem.

The GSXR stem that I pressed out of a $12 lower triple measures a total of 181mm bottom of lower bearing seat area to top of upper bearing seat area. 8.5mm shorter than your V-Strom DL1000 steering stem pictured.

PSX_20221112_143909.jpg

So on this GSXR stem, I am measuring approximately 30 mm from the very bottom point of the entire stem, up to the bottom of the lower bearing seat or top of the press-fit area.


Holding the GSXR stem up to a Suzuki GS stem, the bearing land areas are almost identically spaced!
I Believe that buying a sacrificial GSXR triple clamp off of eBay to donate the stem for the V-Strom DL1000 triples will be a very direct fit for our 43mm fork swaps

This solves another problem I had as well and is why I revisited this thread... Trying to swap '96-'98 RM125/RM250 forks (or 2000-2022 DRZ400S / '00-07 DRZ400E forks) onto a Kawasaki KDX220R... The steering stems for the Suzuki off-road bikes were not tall enough Kawasaki frame!
In order to run these GSXR 1100K forks that I have, The GSXR stem will very likely solve my problem, which will give me a spare DL1000 alloy stem that is longer in the bearing seat areas, which will solve my problem on the '98 RM125W Showa Twin Chamber 49mm conventional cartridge fork swap onto the KDX220R's!
There is a ripple effect here, as going from my markings written all over the GSXR stem, it was still a bit too tall for the Rickman frame that I have as a project on the back burner... The RM stems having an even closer bearing seat area should solve that as well!


John Kat If you have a chance to measure the press fit area all the way to the very bottom of the steering stem on that V-Strom stem, that would be appreciated. I may just buy a set of triples off of eBay since you have already successfully used them I believe with a lower bearing spacer or a stem swap, I'm pretty certain that this will solve my issue. I may have to recess it up into the Suzuki RM 125 lower triple a little bit more, but It would require the least amount of machine work of all...
Thank you for posting!

[Chuck78]

Also I should mention that in order to run these GSXR1100K forks properly, especially when stepping down in wheel diameter to a 100/90-18 which lowers front ride height which also slows you down in corners as it detracts from your lean angle before scraping the stator, I plan to make an inverted gullwing type upper triple clamp that steps down approximately 35mm from the top of the triple in the center steering stem area, to the tops of the fork tubes, so that the forks can protrude lower to get back up to proper ride height.
This is what it takes to get a set of 43 mm forks that have fully adjustable compression and rebound. Otherwise, the Bandit forks are the ones to run as they would not need this custom machining.

EDIT - I have not revisited the 43mm Yamaha R6 conventionals for height, but as I said many posts prior, I was amazed at how lightweight they were but then dismayed at seeing a crash damaged pair as they are so thin walled that they creased and buckled on a crashed bike which I inspected.
Other than that, they were incredibly appealing forks, on a very excellent bike. The forks had very good valving and I believe were fully adjustable.
John Kat stated above 740mm for the '89 GSXR1100K forks, 13mm longer @ 753mm for the R6 Conventionals, & 775mm for the GS1000. Both the 1100K and the R6 are substantially shorter, that's why I think the Bandit 1200 43mm conventional forks are the best bet. Honda VTR1000F Firestorm & Yamaha YZF600 Thunder cat 41mm forks are right up there near the top as well and are more appropriate length than the R6 or GSXR 1100K.


Emig Racing is one of the several companies nowadays that will make custom billet triple clamps and custom steering stems as well if you just need to swap to a different stem and can't get the right dimensions easily. This is becoming more and more of a good option these days. Once I tram my Enco RF-30 round column mill had so that it's a bit more precisely aligned, I may give it a go making some custom upper triples.

[John Kat]

John Kat
Revisiting this thread again, I think I might have solved two problems simultaneously!

John Kat If you have a chance to measure the press fit area all the way to the very bottom of the steering stem on that V-Strom stem, that would be appreciated. I may just buy a set of triples off of eBay since you have already successfully used them I believe with a lower bearing spacer or a stem swap, I'm pretty certain that this will solve my issue. I may have to recess it up into the Suzuki RM 125 lower triple a little bit more, but It would require the least amount of machine work of all...
Thank you for posting!

Hi Chuck,

It's been some time ago I mounted the Vstrom triples on my GS 1000 frame with the R6 RSU stanchions...
I don't have access to the press fit area as the bike is fully rebuilt and running.
I do remember however that I thought at first that the stem would be too long but it worked in the end with an extra spacer under the top triple.
It probably could be located underneath the bottom bearing?
You are right the R6 forks are very light and the weight saving is enormous.
Riding the bike feels like a 600 except that it's powered by the 1052 cc GSXR engine.
With the Devil exhaust it's my most exhilarating bike to ride!

[wheels]

Excellent research gentlemen thank you for the info