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Bitubo JBH01V1 closed pressurized fork cartridges

5874 Views 86 Replies 12 Participants Last post by  temporarykiwi
After Installing a XXZ31 rear shock, I found the front cartridges particularly weak on small bump compliance.
They also get very harsh on high compression values.
Several forum members found good improvement of front forks with lower oil level than stock and different grades (5wt, 7.5wt).

Example Oil level curves on damping force from Ohlins NIX22 cartridge for R3:
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I wanted to try the same but I need to get new fork springs and a new cartridge with springs is not that far away price wise.
The stock springs are progressive, starting at 0.82 kg/mm and ending at 0.89 kg/mm creating too much static sag for me (~170 lbs)

Among the front fork cartridge options I looked, most of them are standard open cartridge style (similar to stock) but with different materials, piston diameters/designs and separated fork functions (comp & rebound)
e.g. The stock is 20mm. Andreani is ~22mm, Ohlins has NIX22/NIX30 etc..

Typical standard twin-tube fork cartridge design according to Lee Parks Suspension Bible:
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One big problem with open cartridges is cavitation (esp. on cartridges with both comp and rebound)
A very good demo about it:

The other design used heavily in racing/Motocross is the Spring/Gas pressurized closed cartridge system.
which is supposed to deal with cavitation much better and give consistent damping.
The biggest problem with this style of cartridges is you need to take them to a service center for rebuild if it's gas based.
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Showa's BFF fork used in GSXR-1000R/ZX-10R, Ohlins NPX in R1M, CBR1000RR-R/V4S/V4R are the OEM pressurized cartridge options I can think of.

There are very limited aftermarket pressurized cartridges on the market with Ohlins FKR, Bitubo JBH/EBH/ECH, Ktech DDS, Andreani pressurized, WP Apex pro 7500, FG Gubellini, MUPO CSP30 being the options I could find. Unfortunately all these 30mm pressurized kits are very expensive, racing only and require maintenance frequently as suggested by the manufacturer (at around an year/10k miles or 10 hours of track).

Bitubo JBH (previous model ABB) seems to be an exception given it's a simpler and smaller (22mm) design has higher service intervals 20k miles.

I found a service manual for it and looks like the cartridges are closed style, with 22mm pistons and pressurized with nitrogen at 8bar.
The gas and the oil are separated by a floating piston with two rubber o-rings, similar to decarbon style rear shock.

So, I've ordered a set from an Italian retailer with the correct set of springs for me at 0.9 kg/mm which came out to be ~550$ shipped.

I just received them. Will install and report the details after the ride.
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This would be a typical flow most people would recommend and there are multiple youtube videos explaining every step.
It's a bit daunting for beginners but getting a feel for these setting changes on the same road is the only way. Experiment. A lot.

1. Set your suspension sag correct for your weight.
Adjust preload only. Aim for ~35mm for street. ~30mm for spirited riding. ~25mm for track. This makes a big difference than you think.
If you can't get these recommended values with reasonable preload, time to get new springs.
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Follow a consistent method in measuring sag that accounts for sliding friction.
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2. Set rebound.
Start with default setting. Do a bounce test and set it to a baseline value where the bike bounces back and settles after overshoot quickly.
Then start experimenting and fine tune it. Rebound determines your dynamic ride height.
Tightening rebound will get a good road surface feel till a certain point before becoming harsh on the forks. High rebound on the rear doesn't give you any 'feel'
Loose rebound will feel good at leisurely pace but the bike wallows a lot when the pace picks up. Forks will jump up before corner exit. Shock will pogo and jump during braking.
From my experience, the rear doesn't need as much rebound damping as the front as we need rear up faster than the front for better geometry during corner exit.

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A lot of folks typically add more rebound damping than required. But it's good to have a bit less than what feels good.

3. Set Compression damping
I feel compression is a little tricky to setup. Start with the default setting.
Experiment to see and add (a little less than) as much as you can based on your suspension stroke length usage and feeling of control.
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Few things to keep in mind:
- Your tire pressures play a huge role. At typical stock 36/42, your ride will be rough.
I would recommend ~33/33 to start with for street/canyon riding which reduces a lot of small bump harshness.
This can vary based on tire carcass type and style of riding

- Suspension fluid fill level.
As stated in the first post, the stock forks have way too much fluid.
This would make it very difficult to use more than half the stroke length.
Tie a zip-tie to fork tubes to check for stroke length usage.
In ideal conditions, you should be able to use most of the fork stroke except the bottom ~1.5 inches.
Try reducing the fluid level.

- Tire wear patterns.
Keep checking periodically how your tires look. Wear patterns can tell you a lot!
Keep in mind that street riding wear will typically look like low rebound damping wear. (leading edges of tire blocks taller than trailing)

- Quality/Architecture of suspension components
Some forks/shock adjusters only work on a limited range of their provided adjusters.
Stock fork is pretty decent in this regard. Stock shock, utter garbage.
Solid piston TTx style shocks/forks due to their architecture typically ride much better.

- Top out spring strength.
The stock top out spring is a bit weaker than I like.
This might cause more than required force for the whole fork to start working at the top of the stroke

- Geometry/ride height
No amount of suspension can fix handling woes caused by geometry.
GSXS inherently has higher rake angle and longer wheelbase than a GSXR which makes it much more stable but lazy to turn.
Make sure the front/rear are balanced when you adjust compression/rebound.
Front low, rear high dynamic ride height typically gives you the best turn-in/corner exit. So take it easy on rear rebound. If possible, raise the rear shock height.

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Dang it, I guess 4 hours isn’t that far. There’s another place there that my friends have used called Fast Bike Industries. Thanks for the psi idea and other input
Just ordered my Bitubo JBH yesterday (y)
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My JBH is almost here so I'm doing some homework on how to do the install... from looking at it, I don't understand yet why the cartridges have to come apart. From looking at the gsx's part fiche- if I can rattle out the bottom bolt and unscrew the upper tube from the cap, doesn't the cartridge lift right out- no need to remove the cap and spring and so on?

And to that point, is there any difficulty with clamping the upper tube and using a suitable wrench to unscrew the cap?

You can start first with either the top caps or the bottom cartridge bolts, but draining out the fluid is much easier with the top cap first.
If you have bottom cartridge bolt removed as well, yes, the whole cartridge can come out.

Loosening the fork top caps while they are already attached to the bike would make your life easier later.
I did not do that and had to stick the fork tubes in a vise for loosening the top caps.
Make sure you have the correct socket ready. For Bitubo JBH, I guess it's 28 or 29 mm socket.
Hi @gpounce, Did you finish your install? Interested in your upgrade impressions.
Have it waiting for some downtime... I have the fork spring compression tool and fork oil- all the stuff is ready. Kind of want to make some tooling for the press to make the spring compression easier. After I put the Penske rear in the ride got so much better than the priority of getting the front end done decreased a good bit lol
Very interesting info. I would love to install the cartridges, but when you go to the suppliers site they only show that the fit is for the 2019 and up Katana. Now I quickly looked up the fork parts break down between the 2016 GSXS1000 and the 2020 Katana, there are a few P/N difference but I don't think any internals. I think the upper outer tubes are different but I believe that might be colour. Any able to confirm if these Bitubo JBH01V1 cartridges will fit older GSXS 1000's. Thanks
I think they should fit. Older fork tubes has compression screw that clicked between settings. Other members can confirm
ok starting to get moving on putting in the cartridges. It took a bit of time to work up the press tooling to compress the fork springs the way I wanted. Though I <think> this job doesn't necessarily need the caps removed from the forks, I wanted to figure out how to do so since I've never done it before. Here's a pic of the rebound cart in the press;

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It does fine job of compressing the spring, I wanted to confirm a few details before pushing on. 1st, does the jam-nut beneath the cap move at all- meaning is it fixed in place on the threaded rod coming out of the cart?

It seems that the piston turns easily in the cart, so thats perhaps why. I've compressed the spring a couple times to see how to fit the traxxion spring retainer tool beneath the nut, to get the spring out of the way and allow the cap to come off. The tool from the traxxion kit is just a bit too thick to fit beneath the nut (interference with the cartridge body. I cut a new one out of .060" aluminum which fits the clearance between the nut and piston body and works fine, but the nut wants a thin profile wrench...

The rebound cart feels as if it has a spring inside which retracts it down as the fork spring is compressed, doesn't take much to pull it back up to expose the locknut above the top of the spring. I'm assuming the compression cart will be similar?
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Make sure you turn out all the clickers on the top cap and install it on the cartridge threaded rod. The jam nut is then locked to the top cap.
Yes, both the cartridges are gas filled. Hence even without spring, the piston rods need some force to pull/push.
I made up a wrench for the JBH's rebound cartridge locknut, tried to take the top cap off but it looks like Bitubo shipped it torqued tight; attempting to unscrew it just rotates the preload adjust inside the cap which is pretty cool- I was wondering how that worked. So I'm going to defer going in further since its already tight. There are a couple other flats I could make a wrench for if taking the cap off is really necessary, but I'll skip doing that unless there are substantial problems getting the bottom screws tight.

I'm confident with the press now so I'll go ahead and do the conversion- naturally I'm away this weekend but if work is quiet on Thursday I'll get after it :)
Got home late, not enough time to do the forks so I experimented more with the JBH, removing and reinstalling the caps. The nut needs a 17mm thin open end wrench (eg 3mm thin wrenches work great), and a 31mm open end thin wrench is also needed. Regular open-end or crescent wrenches are too thick. For the 31mm wrench, I found a Rockshox bicycle suspension wrench.

With the spring compressed by a keeper tool inserted beneath the locknut, the 17mm wrench goes on the locknet. On the bottom portion of the cap, beneath the fork tube threads, there are a pair of wrench flats that take the 31mm wrench. If you put a socket on the cap top nut (28mm), you can't take the cap off because it will rotate the preload adjust instead.

Using the 17mm and 31mm wrenches, the cap unscrews in the usual way. The rebound/compression adjust works against a shaft which runs down into the shock, inside the screw. Preload is applied by screwing the inner portion of the cap down against the spring- the preload adjust runs on its own threads inside the cap. There are no keying or other alignment features between the cap and the threaded rod onto which it screws- just tighten it down against the locknut to reinstall.

Note, the JBH shocks include a little plastic nut which takes a 17mm wrench/socket on one end, the other fits over the preload adjustment. The allen screw head seen at the center of both forks adjusts the damping (compression on one for, rebound on the other).

Both of my JBH's were shipped with the caps fully tightened against the locknut, its worth checking because the Bitubo documentation implies the caps are not shipped tightened, the manual suggests the cap is usually taken off to assist with installation of the shock assy into the fork so it may only be finger tight.
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Theres not many days suited to riding around here in December so I dove into installing the JBH's. I've not tested them yet (being its Sunday night now), so this post only includes observations on installation.

I rigged the bike with my shop crane so the tire was just free of the ground, and easily lowered when traction was needed (eg loosening/tightening the axle bolt- 1-1/16" socket fits it well). The ropes are looped through the rearward engine support bolts which afforded a nice straight lift. The strap is there around the neck for safety, just a bit of weight on it.

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When removing the forks, after loosening the binder bolts give a light pry with a screwdriver in the gap to open the lower clamps enough for the fork to slide freely- also helpful when reinstalling them.

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Remember to loosen the top clamp and unscrew the top caps a turn or so before removing the forks. Makes it way easier to remove the caps when its time to drain the oil. I used a 24mm socket which is a good fit on the top cap hex flats. The factory fork oil is quite low viscosity, maybe approx 0W.

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My 3/8" drive electric impact didn't have enough grunt to take the bottom bolts out- I had to use an air impact- perhaps a big Milwaukee or equiv electric would work too. DO NOT use a round-tip allen wrench bit for this- the bolt head is quite shallow so is prone to wallowing out unless a proper allen is presented- I nearly had to drill out the bolt on the right fork but thankfully saved it. I used the 3/8" electric impact to tighten the bolts with the JBH's, and put on new copper washers. Using hand allen wrenches without the holding tools and so on would surely spin the cartridge. The impact wrenches get the fasteners spinning (or tight) really fast so the cartridge (hopefully) doesn't have a chance to spin.

The Traxxion fork servicing kit mentioned previously in this thread comes with a blister-packed set of 3 different sizes of allen keystock, 8mm included. With one end of the 8mm allen in a socket, the other would reach the fork bottom bolts, so no need to risk using a ball-end or buy something special. I only realized those keys were in the kit while I was putting the tools away :rolleyes:

While on the topic of the Traxxion kit, when I was experimenting the disassembling the JBH forks I found that some short lengths of PVC pipe cut lengthwise could be fit between the fork compression tool and the spring to help keep the tool positioned- I scavenged the plumbing scraps drawer to find suitable bits and cut them to shape. IIRC I used a 1 1/2" union cut lengthwise and holes drilled for the two handles, then some 1-1/2" pipe cut similarly to nest inside of that.

When installing the JBH's, I turned out the forks' comp screws a bit, then tightened them down to snug when everything was reassembled.

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I did not disassemble the JBH's before installation (take off the top cap and spring). Consequently I could not measure the fill height of the new fork oil. I followed k2t2's experience, where he had 300ml left over- which means 350ml per fork. Thats perhaps the only downside of not disassembling the forks. If either bottom bolt turned into a problem then certainly further disassembly would be needed, along with the cartridge holding tools.

Before putting the forks back in, I screwed the upper tubes onto the upper cap till finger tight. As a last step before tightening the top clamp bolts I tightened down the caps- they take a 28mm socket but mine was too tall to fit along with the wrench (handlebar in the way), so I used a crescent wrench instead.

This job looks way scarier than it is to do OTOH if things go sideways (strip out the head of a bottom bolt, impact just spins the cart without loosening/tightening) then the variety of suspension tools will certainly be needed. I didn't end up needing all the prep for the screw press- normal shade-tree methods worked fine.

I set both shocks to the defaults in the manual (12 clicks in for damping, 4mm preload). The center allen screw provides damping adjust with positive clicks. I couldn't feel any definite clicks on the preload so instead put a bit of tape w/ sharpie mark on the tri-lobed plastic adjuster nut and followed the specs; 1 mm per turn. The manual says preload has a click at every half turn- I was using a fairly long wrench perhaps a shorter one would provide better feel. Both adjustments back out to a positive stop so its easy to know where you are. The red anodized collars on the top caps are fixed- they don't move as preload is changed; you have to go with clicks/turns.

Total time wrenching maybe 3hrs. We'll see how they ride on the next reasonable day...
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Can’t wait to hear your impressions. I look at it like you’re making a bike that competes with the Euros with reliability.
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We eventually made it out of our very deep freeze, enough for a short test ride; digging around some local roads a bit of heavy braking and a brief highway blast, seeking potholes, pavement seams and so-on.

The JBH's are certainly quite a bit nicer than the OEM's- better shocks than I am a rider lol

I started with the JBH defaults which are a reasonable beginning... perhaps illustrating the weaknesses of the factory forks. Small bump compliance, particularly at highway speeds is clearly improved. I found the OEM's harshness a source of fatigue on longer highway rides... constantly a bit rough when the pavement was not smooth- those harsh edges are substantially moderated. Detailed road feel is very much there, but not disruptive.

A wiretie shows I'm close to bottoming if not actually, theres a bit of room left from rider sag so I'll push the preload up a bit more. Off the top of my head I'm probably heading towards settings much like k2t2's.

Background searches on others' experiences with the JBH's back in circa 2018 gave the impression a few people had trouble with stiction and difficulty with adjustment, I had no sign of those issues.
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Sure am waiting for better riding weather in the spring, but I got a 3hr ride in over the weekend. This time I went further afield- a greater variety of roads etc. The improvement over stock is noticable, fast or slow. I'm still at close to factory default settings, but getting more fork travel than I like when braking so continuing to explore preload and comp damping. Defintiely a good upgrade, the forks are way more comfortable on long rides.

Searching around a bit, there are other fork carts specc'ed for the gsxs/katana which compete with the JBH's in features and price, though apparently even less info out there about them.

Andreani Misano EVO
FG Gubellini STEALTH

BItubo also has their EBH line, though thats easily twice the price of the JBH's
Thanks for your impressions gpounce!
If you are having more fork dive than you like even after preload/compression adjustment, the spring might be softer for you.
As a quick fix you can raise the oil level by ~10-20 mm in the fork legs.

My Zip-tie still shows ~25-30mm fork travel left which is inline with champ school guys recommendation.
Forks should be compressed by no more than 100mm for perfect cornering geometry
Bitubo sells springs in the range of 0.8N/mm-1.05N/mm for JBH. I plan to get MX82(1.0N/mm) this summer if I can improve my riding. Stock is 0.9N/mm

FG Gubellini stealth : KIT CARTUCCE COMPLETE - FG Gubellini
Andreani Misano Evo : Andreani Misano Adjustable Hydraulic Cartridges for Kayaba 41 for Suzuki Gsxs1000 F 2016 2019 - 105

Both of these are traditional twin tube architecture cartridges just like the OEM KYB, perhaps with different valving.
A lot of people found Andreani valving to be stiff. Not sure about FG.

Bitubo EBH is similar to Ohlins FKR and other pressurized cartridges in ~30mm piston class. These track class cartridges provide more damping and are $$$$
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Good idea about raising the oil- easy enough to do, I was wondering a bit about that. I did get .96 springs IIRC but I'm not bottoming in any harsh way though. Probably could go for a stronger spring- at 7mm preload now, will put on a couple more and observe. Probably will go for more oil instead of going past 10mm I think.

But its not off by a lot, my zip tie seems to be holding OK at max travel I just get there a bit too easily. That said I'd rather have it a bit too soft than a bit too hard. The bike corners great though.
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The factory preload tool was getting a bit annoying to adjust using a 17mm combo-wrench- my bars preclude using a socket, even a swivel socket- so I made up a replacement, drawing is below. I also couldn't find an obvious way to buy another factory tool (I like having spares for idiosyncratic tools like this). Material is 6061 aluminum. 3d printing materials would probably be OK too.

The 8mm socket-head screw fit to it allows the use of ball-tip allen wrenches which makes adjustment easy even with the wrench off-axis. I have a dxf file but apparently I can't attach such things on this forum.

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