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2020 Suzuki Katana 1000
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Discussion Starter · #1 · (Edited)
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:
Rectangle Slope Parallel Font Plot


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:
Rectangle Slope Font Line Parallel


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.
Product Font Parallel Rectangle Slope


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 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.
Rectangle Wood Floor Gas Composite material
Tower Skyscraper Camera accessory Camera lens Gas
Font Office supplies Writing implement Parallel Illustration
 

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Funny enough I have just spent some time looking for replacements for my bike and came across this set up.
They seem to be the only ones out there that come complete and ready to install.
I will be interested to see how you get on with the installation and getting them set up and then how they feel on the road.
 

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2020 Suzuki Katana 1000
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87 Posts
Discussion Starter · #6 · (Edited)
I have finally managed to install the cartridges and it was mostly painless except for compressing the spring to fit the fork caps in the end.
I removed the stock fork internals as per the manual with Traxxion dynamics fork cartridge toolkit and a Biltek KYB cartridge holding tool.

Tire Plant Automotive tire Automotive lighting Wheel



Initially I was worried if the fork bottoms have to be removed, but I was happy to find that the cartridges are direct drop-in.
Cartridge bottom:
Street light Cylinder Electric blue Auto part Pipe

Fork Inside after stock cartridge removal. (I backed out the stock compression screw)
Automotive lighting Automotive tire Liquid Fluid Automotive design



Filled with Silkolene 02 synthetic fork oil (not provided with kit) up to 150mm as recommended.

After riding my favorite twisty, JBH with the 0.9kg/mm springs gave me a huge improvement over stock on small bump compliance.
I've tried higher compression settings as well and they don't seem to make the ride considerably harsh unlike the stock cartridge which was unusable beyond 1.75 round out of compression for me. The nitrogen gas must be helping a lot with small bumps.

I have started with recommended settings comp: 12, rebound : 12, preload: 4mm
After some testing ended up with 9 clicks out on comp, rebound and 10mm of preload which helped reduce brake dive and improved front end feel.
Lower oil level makes a lot of difference in linearity of stroke. I was able to get lower into the stroke without any harshness!

Finally the bike's front and rear suspension are at similar level and the damping feel at the front is now the same at the start of the ride (vs) after 1-2 hours of hard riding unlike the stock which would drop off after hard riding.

The cartridge damping feel is quite linear (similar to stock) unlike the XXZ31 rear shock which is clearly digressive feel with a solid piston TTx style design.
I guess the shim stack is tapered and not preloaded.

A lot of suspension experts seem to prefer the linear feel but I like the initial firmness from a digressive damper.
Showa Damper evolution seems to be going the small piston linear feel route: e.g. Stock GSXR1000 - BPF forks - ~40 mm piston - feels digressive, GSXR1000R - BFF forks - ~25mm solid piston - digressive feel still (but less than the bpf).

Slope Rectangle Plot Font Parallel


Linear damping rate is good for predictability but feels a tiny bit mushy initially during turn-in.
With a digressive rate, you can feel it when you get on the bike and move it with your feet.
The digressive firmness makes it feel like you have less parasitic spring movement energy losses.

I guess the bigger pistons in (~30mm) Bitubo EBH / Ohlins FKR cartridges would give me the firm digressive damping character I was looking for as they move more fluid similar to Showa BPF/BFF forks, but they are too much $$$$

The cartridge upgrade did not completely blow me away like the stock rear shock upgrade to Bitubo XXZ31. Shows you how bad the stock rear shock was.
Overall the upgrade is fantastic for ride quality and consistency of damping. Maybe I would have picked 0.95 kg/mm springs if I were to order again.

I would highly recommend this to anyone that wants a quality (20-22mm class) cartridge kit for sub 600$
 

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2022 GSX-S1000GT+ blue
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While I’m a decent rider, I only do it for fun on weekends. Getting that technical might take the fun out for me.
 

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Getting ready to start buying stuff for this upgrade. Confirming the Bestek KYB tool is the "H" shaped retainer device- if so I'm assuming the retainer in the Traxxion kit doesn't fit- or are you referring to the 49mm fork cap removal tool? As to the oil, how many bottles are needed for the suggested fill level?

Thanks!
 

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2020 Suzuki Katana 1000
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Discussion Starter · #15 ·
Oops, I meant 'Biltek'. It's a cartridge holding tool.
Mind you, the length of this tool could run short, if you haven't separated out the inner/outer fork tubes while replacing the cartridge bottom bolts.
The eyelets of this tool would be inside by around an inch with the outer tube completely dropped to it's lowest position on the inner tube.
I've used a screw driver on one of the eyelets as a leverage and an Allen key at the bottom to remove the lower cartridge bolt.

This Biltek cartridge holder won't work on the Bitubo cartridge and requires a special tool
I didn't need this as the cartridge bottom bolts tightened up good and for removal I could use an impact wrench.

I've used ratchet straps for compressing the OEM stock springs.
Reused the copper washers of the bottom bolts as they still looked thick and good.

As I've said, compressing the Bitubo springs is tricky.
I've inserted a wrench on to the cartridge lock nut via the spring gap, twisted the spring till the lock nut comes out at the top.

The silkolene 02 synthetic fork oil comes in a 1 liter bottle. With both cartridges filled to ~150mm, I still have 300ml left.
You can use their Pro RSF 5w oil as well or any other one you like. The oil weight here doesn't matter as it doesn't do any damping.

Tool links:
Biltek damper rod tool: https://www.amazon.com/dp/B08MV6T4Y7
TD fork service tool kit: https://www.amazon.com/dp/B08V6Z3JT2
Bottom bolt copper gaskets: Suzuki 51148-41310 GASKET - RevZilla
Bitubo 00397 cartridge holding tool: Bitubo Fixing Cartridge Tool - Universal parts & accessories - Storm Motor
Silkolene 02 syntetic fork oil: https://www.amazon.com/dp/B09ZQ3T7YY
Silkoleve Pro RSF 5W oil: Amazon.com: Silkolene 601450181 Pro-RSF Shock Fluid - 5W - 1L. : Automotive
 

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Sweet! Thx :) I did a bunch of cross-referencing of parts in the OEM forks this morning, 2022 internals are the same as 2017- so looks like no problem with compatiblity. Will be an adventure, I've only ever been inside 80's vintage forks... :)
 

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ah- working through your list; So the Biltek tool is to remove the OEM cartridge, the Bitubo 397 to install the replacement (this tool might not be needed if the bottom bolt doesn't spin the cartridge). The tricky bit is restraining springs (both OEM and Bitubo) while separating/reattaching the upper cap and cartridge body.

I see from first posts you did not have to remove the fork bottoms (which looks like it would be a bit of a pain for sure). Some other Bitubo upgrades provide replacement plugs for the fork bottom adjusters. For this upgrade I have the impression the old adjusters are left in place and have no effect?

Fork oil no longer provides damping, just an air cushion effect.
 

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2020 Suzuki Katana 1000
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Discussion Starter · #18 ·
Yes. I left the old compression adjusters in place. They don't obstruct anything.
I guess, you won't even need the Biltek tool to remove the OEM cartridge as a lot of folks had success with impact wrench.
 

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2022 GSX-S1000GT+ blue
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After a rather "spirited" ride with my sportbike friends this weekend in the twisties, I feel the forks need more help than the rear shock/spring. It may have a lot to do with my bike not being set up for me yet. Anyone know someone knowledgeable and capable near the Raleigh NC area?
 

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Cogent Dynamics
33 Meadow Brook Dr.
Fletcher, NC 28732


They were the go-to suspension shop on the old Maximum-Suzuki forum- lots of Bandit folks sent shocks down there (me included) for gold valve replacements and so on.
 
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