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Showa TC-47 Pressure Springs


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Hi everyone, '06 KX250F. Showa TC47mm forks. Resprung for my weight (178). Vet Junior MX. I'm trying to understand the relationship the ICS pressure springs have on fork plushness. I've heard that going to a softer inner cartridge spring can have a noticeable effect on small chop and braking bumps etc. Doesn't seem like it's often discussed, so has anyone got some insight on this? I certainly would like more plushness in the initial part of the stroke, but like everything in life, nothing is free. So if I did go to a softer ICS spring, what would the downsides be? I understand that with less pressure applied to the inner cartridge, the fluid may cavitate more easily, should I be concerned about this? I run 370cc of oil in the outer chamber, and even on really big jumps if I bottom the forks they're not that harsh.

Edited by Slick_Nick
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I have had that done by a couple tuners and the forks felt like they were sagging and were not rideable in the woods. Could not feel what they were doing and I could not trust them. Did not work for me, just cost me money. .

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They seem to be quite misunderstood. The ics spring works the same as the nitrogen pressure in your shock. It will add a small amount of 'spring' to the forks, that's it. If you reduce the rate you promote cavitation, which is what they are there to prevent.

How much preload do you have on the main spring?

The other thing is when were the forks last rebuilt? The Showas seem to bind a lot when everything gets a bit of age under it, new bushes and seals will do wonders sometimes.

There's much better options than softer ics springs.

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16 minutes ago, DEATH_INC. said:

They seem to be quite misunderstood. The ics spring works the same as the nitrogen pressure in your shock. It will add a small amount of 'spring' to the forks, that's it. If you reduce the rate you promote cavitation, which is what they are there to prevent.

How much preload do you have on the main spring?

The other thing is when were the forks last rebuilt? The Showas seem to bind a lot when everything gets a bit of age under it, new bushes and seals will do wonders sometimes.

There's much better options than softer ics springs.

Forks were rebuilt completely about 10 hours ago. New bushings, seals, etc. No binding in the forks, cartridge seals are new and not leaking. Installed heavier springs for my weight (4.6N/mm) direct from Kawasaki. Springs have no added preload, these forks only have the one circlip groove to locate the upper spring perch. 
 

ICS springs have bo preload, there is about 5-7mm of free play in the IC piston that is taken up when the cartridge is bled. 

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4 hours ago, Slick_Nick said:

Forks were rebuilt completely about 10 hours ago. New bushings, seals, etc. No binding in the forks, cartridge seals are new and not leaking. Installed heavier springs for my weight (4.6N/mm) direct from Kawasaki. Springs have no added preload, these forks only have the one circlip groove to locate the upper spring perch. 
 

ICS springs have bo preload, there is about 5-7mm of free play in the IC piston that is taken up when the cartridge is bled. 

Still, check the preload on the fitted springs. My CRF forks had about 6mm, I dropped it to 3 ( I machined a new groove)

Edited by DEATH_INC.
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Quick update, after some further research it appears as though my forks on the '06 come stock with a 1.9 ICS spring installed, while in '07-'08 Kawasaki / Showa decided to use a 1.4 instead. I've confirmed the part numbers are different for those years vs my '06, and the Kawasaki specs for '07 list "fork valving changes" as one of the updates. Likely the ICS spring change was part of this. I think I will try the 1.4 spring and see how it works.

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I had experimented softer ICS springs in both my CRF250X and YZ125 and, have gone back to stock springs on both.

Nothing scientific (backyard suspension tinkerring) but here are my observations:

 

Unlike the CRF250R MX race bike version (w/1.9's), the CRF250X (off-road) already came with 1.5's as stock,

as a 1st tuning experiment before serious revalving I tried 1.4s and despite what would seem was a very

minor change I immediately felt it rode lower in the stroke.

Perhaps plusher at very slow speeds and on the initial hit but, packing down on successive hits.

True plushness on trail trash, roots, rocks & logs eventually came from much softer midvalve,

firmer up low speed and, relatively fast rebound valving.

 

YZ125 by memory comes stock with 2.0 or 2.1 springs,

for a while ran a pair of 1.8's but as my skills progressed, 

hitting bigger jumps I felt/heard the forks 'thud' on rebound while airborne. 

Figuring it was cavitation, I re-installed the stock springs and that issue is now gone.

 

Also learned that preloading / taking out the free play in the ICS springs is also a no-no,

eliminating a lot of terrain compliance in the first few inches of travel.

 

IMO differing from the factory rate / intended usage on ICS springs as a first mod is only a band-aid for proper main spring rate & valving.

 

Edited by mlatour
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I got some 47mm Showas in my 2010 KX250F and got them working really well. Stock ICS but no idea what rate they are.

Soften the base was not the fix for me. Actually I ended up with a very firm base stack.  Single stage. Not harsh at all. But quite firm. For MX tracks only.

20 hours ago, mlatour said:

True plushness on trail trash, roots, rocks & logs eventually came from much softer midvalve,

This is what I found too. For rough MX. The mid is the business zone.

Soft on the base (as is stock) reduced consistency for me. I guess because of oil cavitation.  I use stock springs. I'm 165 lbs. 360ml of outer oil. Good smooth bottoming resistance in the current setup.

In the mid comp I ended up with 0.25mm float gap, which is tighter than the stock 0.3mm. But the fork is still smooth enough for a MX bike over rough chop.  My mid working stack is also 20% firmer than stock. But my forks are far more plush than stock over sharp stuff because I increased the maximum open deflection in the mid comp. My records don't explain how much vs stock, but you can let yours blow open an extra mm without risking shim deformation.  To do this you need to change the height of the collar supporting the piston and the thickness of the clamp under the mid stack. My mid stack is 2x20.1 19.1 18.15 17.1 2x16.1 over a 12mm clamp.  From memory, the float spring pushes on the back of the 16mm.

My reb stack is near stock. I just moved the x-over shim to be 2 positions close to the face. So less damping at low reb speeds.  Found by trial and error. This helped the front tire feel more connected to the dirt.

I think you can allow the mid shims to blow open a lot further, if the base is setup to take over the extra damping force. And you can avoid VHS damping spikes in the base by using a smaller diam clamp shim with more working shims.  I don't know what Honda do, but Kawi use some crazy large diam clamp shims in the stock base so the base valve cannot blow open very far. Makes no sense to me.

 

Edited by numroe
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15 hours ago, DEATH_INC. said:

18.1 base pivot on top of a 30mm plate in the CRF forks I have.

The 2010 KX250F stock base has a huge 21mm clamp.  The face shims are only 30mm. So that just 4.5mm of overhang, which means not much port flow at high oil velocity.  That's the problem with stock Kawi valving in these otherwise great forks. IE. Not enough oil flow in base AND mid at very high stroke/oil speeds.

I went for a 14mm clamp with a much stiffer stack to bend over it. I needed to use some 0.15mm thick shims to stay within stack height limits. I like to setup my fork damping so the clickers are about 12 out for ample initial bleed and easy very low speed travel, then quite firm damping up to the high speed, but for very high speed, I like it to flow more.

My base (for MX only) is: 15x30.1 29.1 28.1 26.1 25.1 3x24.15 22.1 2x20.15 18.1 16.1 14.2c

For off-road I'd prob remove about 25% of this base stack, and same in the mid comp. Reb I'd only change if I changed springs.

Edited by numroe
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On 8/6/2021 at 8:00 AM, numroe said:

I got some 47mm Showas in my 2010 KX250F and got them working really well. Stock ICS but no idea what rate they are.

Soften the base was not the fix for me. Actually I ended up with a very firm base stack.  Single stage. Not harsh at all. But quite firm. For MX tracks only.

This is what I found too. For rough MX. The mid is the business zone.

Soft on the base (as is stock) reduced consistency for me. I guess because of oil cavitation.  I use stock springs. I'm 165 lbs. 360ml of outer oil. Good smooth bottoming resistance in the current setup.

In the mid comp I ended up with 0.25mm float gap, which is tighter than the stock 0.3mm. But the fork is still smooth enough for a MX bike over rough chop.  My mid working stack is also 20% firmer than stock. But my forks are far more plush than stock over sharp stuff because I increased the maximum open deflection in the mid comp. My records don't explain how much vs stock, but you can let yours blow open an extra mm without risking shim deformation.  To do this you need to change the height of the collar supporting the piston and the thickness of the clamp under the mid stack. My mid stack is 2x20.1 19.1 18.15 17.1 2x16.1 over a 12mm clamp.  From memory, the float spring pushes on the back of the 16mm.

My reb stack is near stock. I just moved the x-over shim to be 2 positions close to the face. So less damping at low reb speeds.  Found by trial and error. This helped the front tire feel more connected to the dirt.

I think you can allow the mid shims to blow open a lot further, if the base is setup to take over the extra damping force. And you can avoid VHS damping spikes in the base by using a smaller diam clamp shim with more working shims.  I don't know what Honda do, but Kawi use some crazy large diam clamp shims in the stock base so the base valve cannot blow open very far. Makes no sense to me.

 

So going back through my notes, when I bought the bike it had the suspension done by ENZO. I never rode the bike in that form, (the forks didn't even have oil in them the seals were so bad.) The ENZO setup was done by the guy who was about 4 previous owners ago, so I had no idea what or who it was valved for. I decided to put everything back to stock, and keep detailed notes on what enzo did.

Looks like it was spring (front and rear) for someone roughly 160-180 lbs. I believe the stock 1.9 ICS are still installed, as it didn't look like anyone had touched the lock nuts when I went in there. As for the stacks, it looked like they added the following to the low speed comp (everything above was stock)

30.2

30.15

30.15

30.10 x 13 (stock begins with 30.10x12)

Rebound was stock, and in the midvalve they swapped the 4 20mm shims out for 21mm.

 

This seems to jive with your findings as to stiffening up the low speed compression. Now, I know companies like enzo etc closely guard their secrets, but I don't think I'm airing to much here as I have no idea who that valving is set up for. It may or may not work for me. Now that I've got about 40 hours on the stock suspension (resprung for me) and I'm very familiar with it, I believe I'll put it back to Enzo spec and see how it works out for me, both in the forks and the shock. I'll give that a try before I go to changing ICS springs and stuff which is what this thread is originally about. I'll pull the springs while I'm in there, I guess aftermarket ones will have markings on them if they've been replaced. Maybe that was part of what Enzo did while they were in there?

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14 hours ago, Slick_Nick said:

As for the stacks, it looked like they added the following to the low speed comp (everything above was stock)

Stock 2010 base damping was also too soft for MX. What ENZO did seems to match my base changes. But I used a smaller clamp for softer VHS.

That's interesting ENZO chose 21mm diam face shims in the mid comp. Larger than necessary to close the ports. I guess that would produce a different damping curve.  I might try that one day when I have them apart and can look at them to think about it.

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1 hour ago, numroe said:

Stock 2010 base damping was also too soft for MX. What ENZO did seems to match my base changes. But I used a smaller clamp for softer VHS.

That's interesting ENZO chose 21mm diam face shims in the mid comp. Larger than necessary to close the ports. I guess that would produce a different damping curve.  I might try that one day when I have them apart and can look at them to think about it.

Yeah, now that I'm getting progressively faster on my bike, even with the "stiffer than stock" springs, I can tell I'm riding too fast for the now stock suspension. It lacks a lot of plushness on the small stuff, which is why I started this thread on the cartridge spring swap in the first place. I've messed with clickers till the cow's come home, and I couldn't get the forks to soften up. They do seem to be better if I go stiffer on the compression clickers, which tells me that I'm riding too fast for the stock valving, and it's causing the forks to ride deep into the stroke where they're harsh. I reckon I'll give this Enzo stuff another try, the forks and shock are due for an oil change anyways. I'm sitting at 380ML of oil in the outer chambers, I may even increase that to 390, I have bottomed the forks off a couple 110' foot er's at my track, hurt the wrists a bit.

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Posted (edited)

As for the shock, they simply added two more face shims to the low speed compression stack, and went up 1mm on the clamp shim. Rebound was stock, however I did not disassemble the compression adjuster at the time (I will this time around) to see if they modified anything inside of that. Is that something suspension companies usually do? Or do they mostly leave the adjusters stock?

Edited by Slick_Nick
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