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How to: Make Closed Chamber forks plush for woods riding

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Unfortunately this is not a thread by me informing you of all the tricks and mod to accomplish this impossible feat rather one for us to collaborate on and summarize what success you have had.

The forks I'd like to modify are 47mm TC Showa from a 2006 CRF250R.  I'd like to use them for riding rocky rutted hardpacked woods.  It's my understanding the TC forks are not designed for fast suspension speeds so are harsh when used in such terrain.

Recommendations I've gotten so far:

- Use 2.5wt fork oil

- Do not fill the inner cartridge all the way full and/or use a softer reservoir spring.

Seems like the few discussions I've seen on revalving for plushness did not produce the desired results.  I'm thinking there is some other aspect to this fork which is the "choke point" that limits fluid flow so revalving will have limited gains.

I've searched for info on this subject but haven't found a summary of best practices.  Please share any links or thread titles you have found to be useful.

Edited by MetricMuscle

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Set em up similar to the forks off the crf250x or 450x, those work fine in rocks.

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7 hours ago, biglake said:

Set em up similar to the forks off the crf250x or 450x, those work fine in rocks.

Everything I've seen discussed suggests that the "X" forks are still too harsh in the rough stuff where suspension speed is faster than what you would encounter on an MX track.

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A tuner set up my CR250 forks to be like X forks once, it was a total fail in the woods. Overall it was a little worse.

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When I picked up my '03 CR250R a few years I added Racetech gold valves (and the recommended shims stacks) and changed the inner chamber springs. My forks are super plush yet still feel stable no matter what I ride in or how fast. In fact the faster I go tye better they feel. Rocks, roots, doesn't matter.
A buddy calls them Cadillac forks. I'm 58 and only ride the woods.

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18 minutes ago, carlt828 said:

When I picked up my '03 CR250R a few years I added Racetech gold valves (and the recommended shims stacks) and changed the inner chamber springs. My forks are super plush yet still feel stable no matter what I ride in or how fast. In fact the faster I go tye better they feel. Rocks, roots, doesn't matter.
A buddy calls them Cadillac forks. I'm 58 and only ride the woods.

Wish I had done that, would have saved a huge amt of $$$ and frustration. Several friends have used RT with similar results.

Edited by YHGEORGE

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Wish I had done that, would have saved a huge amt of $$$ and frustration. Several friends have used RT with similar results.


I did the forks myself and had less than $250 in them. Added a gold valve in the shock but had a buddy do the labor because I didn't have the proper tools or nitro. Total suspension tuning was around $450.

A riding buddy has a '13 RMZ 250 and we swapped out his inner chamber springs. That made a huge difference. They were really stiff and it made them a lot more plush. It's the best $40 you can spend on suspension if you ride in the woods.
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5 hours ago, carlt828 said:

When I picked up my '03 CR250R a few years I added Racetech gold valves (and the recommended shims stacks) and changed the inner chamber springs. My forks are super plush yet still feel stable no matter what I ride in or how fast. In fact the faster I go tye better they feel. Rocks, roots, doesn't matter.
A buddy calls them Cadillac forks. I'm 58 and only ride the woods.

This makes sense from what I've gathered so far.  When revalving the shim stack and you get to a point where changes make no difference it is because the piston/cartridge body itself is restricting oil flow.  This seems to be common with street sportbikes too, the aftermarket body has lots larger passages than the OE.

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10 hours ago, carlt828 said:

When I picked up my '03 CR250R a few years I added Racetech gold valves (and the recommended shims stacks) and changed the inner chamber springs. My forks are super plush yet still feel stable no matter what I ride in or how fast. In fact the faster I go tye better they feel. Rocks, roots, doesn't matter.
A buddy calls them Cadillac forks. I'm 58 and only ride the woods.

Did you change both the compression and rebound to RaceTech?

Did you use the Type 1 or the G2-R?

When checking out the ISC spring options, my weight of 180lbs falls right between RaceTech's range, 160lbs or 200lbs.  Would you suggest the softer or firmer spring?

Did you stick with 5wt fork oil?

Edited by MetricMuscle

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250x stack ,

17 hours ago, MetricMuscle said:

Everything I've seen discussed suggests that the "X" forks are still too harsh in the rough stuff where suspension speed is faster than what you would encounter on an MX track.

Did they also drop the spring rate and play with oil level.  I was using  .45 and dropped back to the stock x .42 and 350cc.  happy w clickers right in the middle (12-13).

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Did you change both the compression and rebound to RaceTech?
Did you use the Type 1 or the G2-R?
When checking out the ISC spring options, my weight of 180lbs falls right between RaceTech's range, 160lbs or 200lbs.  Would you suggest the softer or firmer spring?
Did you stick with 5wt fork oil?


I just did the compression G2-R gold valves and two stage valving. I was in between ICS rates as well and went to the softer side.

Yes I used Amsoil light which is 5 wt oil.

While my forks were great, I had Doc @ 812 service them because I couldn't keep seals from leaking because of minute scratches on the tubes. He discovered that while my valving was correct I had some slack in my shim stack causing it to be inconsistent. He fixed it and the forks are even better now. Just watch that if you do your own work.
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11 hours ago, highmarker said:

250x stack ,

Did they also drop the spring rate and play with oil level.  I was using  .45 and dropped back to the stock x .42 and 350cc.  happy w clickers right in the middle (12-13).

Most have tried many different spring rates but don't recall any discussing oil level experimentation. 

How much Race Sag do you have with the 0.45kg/mm fork springs?

9 hours ago, carlt828 said:

 


I just did the compression G2-R gold valves and two stage valving. I was in between ICS rates as well and went to the softer side.

Yes I used Amsoil light which is 5 wt oil.

While my forks were great, I had Doc @ 812 service them because I couldn't keep seals from leaking because of minute scratches on the tubes. He discovered that while my valving was correct I had some slack in my shim stack causing it to be inconsistent. He fixed it and the forks are even better now. Just watch that if you do your own work.

 

Thanks for the great info.

What rate fork springs are you using?  How much Race Sag do you have?

I believe mine still have the OE springs which are supposed to be 0.45kg/mm.

I have 0.46kg/mm fork springs in a different set of conventional forks and only get about 54mm of Race Sag yet I see folks discussing their CRF250R forks having the more proper 100mm of Race Sag.  I think the different air gap in the 2 fork designs is the reason for the discrepancy.

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Changing ICS springs is not the way to attack the problem.  The ICS is to pressurize and strabilize the oil.  Do you drop the N2 pressure in your shock before a revalve?  Of course not.  It also adds to the total spring rate.  If too light on ICS you will induce cavitation, which may feel softer or more active over slower, small bumps, but a bigger problem with control going faster.  Drop your spring rate if its stiff and/or revalve. 

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The stock springs were the correct rate for my weight so I didn't change them. To be honest I didn't measure the race sag. I just slapped them on and rode it. I did change the spring on the shock though based on RT application chart.

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That generation of fork is well regarded; many people swap them onto other bikes.  You should be able to tune them well.

The stock pistons have large ports; they're not a restriction.  Absolutely don't run the inner chambers low on oil, but you can vary the oil height of the outer chambers.

A good woods revalve is a two stage base with greatly softened high speed, a somewhat softened mid with a float in the .25-.30 range, and correct rate fork main springs with minimal preload (there's a lot of preload from the factory).

How much do you weigh?

 

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2 hours ago, GP said:

Changing ICS springs is not the way to attack the problem.  The ICS is to pressurize and strabilize the oil.  Do you drop the N2 pressure in your shock before a revalve?  Of course not.  It also adds to the total spring rate.  If too light on ICS you will induce cavitation, which may feel softer or more active over slower, small bumps, but a bigger problem with control going faster.  Drop your spring rate if its stiff and/or revalve. 

I was wondering about this since the pressure the spring exerts helps to prevent cavitation.  Cavitation will help with harshness but in a "controlled fail" sort of way.

Why does RaceTech sell different rate ICS springs, how do they suggest using them for tuning?

 

1 hour ago, carlt828 said:

The stock springs were the correct rate for my weight so I didn't change them. To be honest I didn't measure the race sag. I just slapped them on and rode it. I did change the spring on the shock though based on RT application chart.

What do you weigh, if you don't mind me askin' ?

 

25 minutes ago, heart_of_darkness said:

That generation of fork is well regarded; many people swap them onto other bikes.  You should be able to tune them well.

The stock pistons have large ports; they're not a restriction.  Absolutely don't run the inner chambers low on oil, but you can vary the oil height of the outer chambers.

A good woods revalve is a two stage base with greatly softened high speed, a somewhat softened mid with a float in the .25-.30 range, and correct rate fork main springs with minimal preload (there's a lot of preload from the factory).

How much do you weigh?

 

I weigh 180lbs.

When you suggest running "the correct rate fork springs" do I use Sag as my guide or some other such method?

Recently I experimented with fork oil level in some simple 37mm Showa conventional damping rod forks.  Even with 0.46kg/mm fork springs I was able to easily bottom with about 10mm lower fork oil than recommended in medium rough terrain at slow to medium bike speeds.  In the past when I've read that the purpose of the fork spring is to get proper Sag or ride height and that fork oil level is what controls bottoming, I didn't comprehend just how important fork oil level and the volume of the air gap really is to the equation. 

I have one of my CRF250R forks disassembled so I will take a better look at the shim stacks currently installed.  I purchased these forks from a tech who says they are freshly rebuilt and valved for a 150lb mid level MX rider.

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There are many opinions on correct fork rates.  If you ride only tight East Coast woods, you may easily find most of the recommendations too high a rate.  These forks provide a lot more damping than e.g. open chamber forks without a midvalve, so you don't need super stiff springs to stop from bottoming.  I weigh slightly more than you and personally found even .45 rate springs to be too stiff in the tight woods; I had to compensate with super soft damping to use full front travel, and handling was still poor.  But some guys prefer that combination.  I'm currently running .42 rate springs with minimal preload and a decent amount of damping: supple over small junk, decent bottoming resistance in moderate single track whoops, and nice turn in. 

But if you ride hare scrambles or MX, you'll want stiffer springs.

Edited by heart_of_darkness
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On the subject of ICS spring rates, from the specs I've found

using similar TC47 forks and bikes of the same era (say '07-'08),

stock ISC spring rates for the CRF250R were 1.9kg/mm , the CRF250X are 1.5kg/mm

 

 

The theory explained in the Suspension Bible suggests using 'just enough' force to prevent cavitation.

I use some  1.4kg/mm in my CRF250X but rather slow to moderate speed trail ride and never jump/land hard.

 

As someone suggested above, softening the mid-valve and high speed stacks plus reducing the fork spring preload

gave the most benefits for my application, like the OP my forks would deflect off rocks even using the stock X valving.

Edited by mlatour
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