Bitubo JBH01V1 closed pressurized fork cartridges

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.


Follow a consistent method in measuring sag that accounts for sliding friction.


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.


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.



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.

Troubleshooting:

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;




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?

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.

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.








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.









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.









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

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.






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...

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.

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 $$$$

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.