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Introducing the KYB PHASE 4 Fork

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And here it is, the KYB PHASE 4 Fork - a home grown build-up that is the cumulative result from just about everyone that has ever posted a question or an answer on the ThumperTalk suspension forum. All that stuff that keeps you thinking and wondering and, well, humble.

It is an old fork made new. Possibly, an old fork made new to be better than anything out there, new or old. It’s not the likes of a hot rod or a big bore kit, but more along the lines of throwing out the old clunky carburetor and bolting on the latest in electronic fuel injection – perfect combustion regardless of terrain, speed or the need of the rider.

It is that good.

It is quite possibly the best fork that any of you will ever ride on. It’s so good that it requires you to re-learn how to ride, to look at a pothole, root or a g-out and say, “So what”. For me, it has removed the fear and brought back the fun in riding. Riding the tracks, the woods, fetching firewood. It works.

I have gone through more fork designs and rounds of testing in my life than Travis Pastrana has done back flips, and this one tops them all. Yes, the KYB Isolated Damping Fork (IDF) was a big step forward, but this one just nails it and confirms the feel of what riding a bike is all about. Have I made my point?

Onward! :mad:

Why PHASE 4?

There are four design aspects that make this fork work, responsive (rapid) hydraulic damping, cartridge backfill, bottoming and ulta high speed blow-off.

Now, some of those can’t exist without one working with the other, making this a very integrated and dependent design. Here’s why.

We have read over and over again all the various complaints that TT users have with their forks. Oddly enough, users will post concerns about a fork that feels stiff but also seems to blow-through or bottom too frequently and in worse case, is soft but seems to push in the corners.

The simplest answer, without providing a solution, is that the problem is one of too much or too little damping. Not enough when you need it, and too much when you don’t. The tuner’s challenge then becomes the process of removing and adding shims in order to flatten and reshape the damping curve but at a cost of compromising performance elsewhere.

DampingChart1.jpg

Here’s what’s happening. In the first chart the low speed damping does not climb fast enough. This is common with mid-valves that have too much float. For these movements, the rider may end up getting an improper balance between spring and oil resistance, which I often refer to as “riding the spring”. During ultra high-speed movements, the base and mid-valve stacks are as wide open as they can get, but they are not able to vent the volume of fluid in such a short amount of time. The reason? Shims are only capable of progressing at a linear or greater than linear rate. In other words, you can never expect a shim to lift to some degree, then ask it to get soft. Once the climb starts upwards, it is never going to flatten or drop off while velocities build.

The real trick is getting a shim stack to behave on both ends of the spectrum. To have ideal low, mid, high and ultra high-speed performance.

Now, while we are on this subject, there is another matter that I call “hydraulic crossover”. It is the process or measurement of when one damping circuit reaches a limit or boundary and another damping circuit comes into play.

For example, most of us know that when you turn a clicker screw you are bypassing the shim-stack. In most cases, the by-pass circuit is so small that the only effect that the clicker will have is towards the bottom of the damping curve. The reason is that the port or hole size of the by-pass can only accommodate a given amount of fluid before it reaches a maximum flow regardless of how much pressure is put on it. This is called “hydro-dynamic lock”.

This means that at some point, the by-pass circuit locks, and the shims on the piston need to lift to accommodate the fluid flows. However, the timing of this “cross-over” is critical in that if the bleed circuit is maximized before the shim stack can lift, you’re left with a hydraulic or damping gap. Without getting too far into this, the trick is to have a seamless and smooth transition in force (resistance) as velocities build.

With that in mind, let’s get back to taking a closer look at the PHASE 4.

The first matter at hand was to be able to build-up a rod stem that could accommodate the works. A blow-off circuit, a configurable mid-valve stack, a limiting device for the mid-valve stack and the rebound stack, and do so with a design that can use both the earlier one piece piston and the later two piece pistons.

This meant laying out all the components and machining a new stem to meet the new spec.

ValveTest2.jpg

And here are what the stems look like fresh off the CNC. These are made from 303 stainless but I can also get them made from titanium ($$).

NewStems.jpg

The next step was to produce the base assembly but this was carried over from the same design that I used with the IDF design. No real change except some additional considerations for load and spacing.

BaseAssembly.jpg

The chart on the left shows the loads that are applied on the blow-off springs via the shim pre-load rings (not shown).

Here are the final pieces.

BasePieces.jpg

The next step was to build a cartridge back fill device without losing the option of using the RSP bottoming cones (more on these later).

This meant that fluid would have to flow in and behind the mid-valve as compression cycles occurred but close and lock the fluid in as rebound cycles occurred – your basic check valve.

However, it’s a tight space and the design would have to be rapid enough to allow the valve to open and shut a few hundred or thousand times a minute, and the flows would have to be generous enough to meet the needs, so to speak.

The fix was to add two sets of three ports into the RSP cone, three on each side that go from the top and outside of the cartridge, and curve and flow downward. BTW - any bubbles that may build up on top of the fluid are well over 2 to 3 inches above the intake ports of the valve.

Then a new strike plate would need to be created to accommodate the flows coming from the RSP cone, and also hold and manage the new check plate and spring.

Conesx2.jpg

CONETower.jpg

SmashPlates.jpg

And here is what they look like assembled onto the cartridge.

cartassem.jpg

AND…this is what the complete assemblies (mid, rebound, blow-off and back-fills) look like before they are put into the cartridges.

completeassem.jpg

completeassem2.jpg

The last item was also a carry over from some of the IDF work and which is obviously part of the PHASE 4 fork. This is, the Double Bottoming System (DBS). This is the integration of a hydraulic end-of-stroke oil lock that also incorporates the factory bumper bottoming system by engaging a fixed amount of the bumper stop before the bottom of the hydraulic stop is reached. This is done by shaping the spring guide and lock nut to bring the top of the RSP cone in contact with the bumper stop. For most of the forks I have built up the engagement is set to 3mm.

Here is a photo to show how these assemblies came together.

dbs.jpg

So that’s it.

Beyond this is the need for others to build up the same fork, or use components of this design with other designs. For example, if a tuner wanted to swap out the existing factory cartridge valves and offer their customers the additional advantages of the bottoming system they could simply use a kit as such.

In other words, the backfill and DBS option should allow the professional tuner or DIY the ability to expand and build out their fork line without having to go to such extremes as adding or building in all the blow-off circuits.

DBSkit.jpg

However, if it were desired, an entire kit as such could also be acquired. This photo shows all the parts used to completely build-up a pair of PHASE 4 forks.

bigkit.jpg

Now, in the spirit of ThumperTalk and the fact that all of this was really derived from the help of others, this fork design is free to anyone who wishes to built it except those that wish to build them for profit. If you have the machining and mechanical assembly skills, I have no problem with providing all the drawings and specs that one would need to go at it. Consider it the equivalent of an open source code. Besides, the more the merrier.

However, I can already tell you that if you had to go out and purchase all the required springs, the RSP cones, the material and machine labor, you’re looking at a hefty price tag. I built three prototypes and each pair was about $600. However, if I purchase and have stuff made in quantity the price comes down significantly. I have yet to figure this out but if there’s enough interest I’ll be more than happy to make it happen.

Lastly, I have mentioned that I am not in the suspension business per say, in that I don’t do the work as so many other readily available shops do. However, this one is a bit of exception simply since it is such an amazing fork. If you have the money and the need, but not the skill or the time to deal with it, I can take in about 10 to 15 forks over the next month. Again, I’ll have to work over a price but I think it can be done for about $375 for the pair. Additionally, this fork has an endless array of configurations for shim stacks and blow-off rates so there is really no end as to how you can tune it and what you can use it for.

Lastly, I guess it is intuitive that for those that always dreamed of the perfect woods and MX fork, this is it.

Now, I own and use one of the three prototypes. The other two have gone out to two other TT members, one of which also has a set of KYB TCs to make a comparison to. Both are advanced and worthy riders and hopefully will have the time to chime in and provide some additional opinions other than my hype.

Let me know if you have any questions.

SPECIFICATIONS

GENERAL

Name: KYB PHASE 4

Type: Inverted Dual Configuration – telescopic KYB – open cartridge – 46 and 48mm

Application: Motocross, Supercross, Woods, Desert

Travel: 11.5 - 292mm

Fluid: KAYABA FR01 Racing Suspension Fluid

Fluid Capacity: 596cc minimum

HYDRAULIC DAMPING

MID-VALVE

Stem: 43mm stem – 303 stainless or titanium– standard porting

Piston: 2 or 4 port 32mm KYB – standard or polished porting

Stack: Configurable up to 14 shims – single or multi-staged

Lift: 24mm limit plate with adjustable shim stop

Blow off: Adjustable compression spring. Rate = 318inlbs/56N

Blow off shims: 0 to 6 – .5mm (.020”) increments

Maximum Blow off rate: 37.77lbs/168N

BASE

Stem: 37.8mm stem – modified KYB base - aluminum

Piston: 4 port 25mm KYB – standard or polished porting

Blow-off shims: 0 to 6 – .5mm (.020”) increments

Stack: Configurable up to 14 shims – single or multi-staged

Lift: 24mm limit plate with adjustable shim stop

Blow off: Adjustable compression spring. Rate = 318inlbs/56N

Blow off shims: 0 to 6 – .5mm (.020”) increments

Maximum Blow off rate: 37.77lbs/168N

REBOUND

Piston: 2 or 4 port 32mm KYB – standard or polished porting

Stack: Configurable up to 14 shims – single or multi-stage

CARTRIDGE VALVING

Type: Multi-port spring loaded one-way check plate

Back Fill: Double sided 6 port – rebound lockout with .33inlbs/.06N clamp spring

Strike Plate: 6 port 303 stainless or titanium

SPRING

Accommodates all standard Kayaba and aftermarket spring sets

Air/Oil: Minimum/Maximum Fluid Level: 130mm/80mm

Spring Pre-load: 10mm preset – adjustable with 2.2mm ring plates

BOTTOMING CONTROL

End of stroke: Double Bottoming System (DBS) with modified RSP hydraulic lock 866 taper plus rubber damper - 3mm engagement

SETTINGS

Base Compression: Standard KYB needle by-pass – 14 settings

Rebound: Standard KYB needle by-pass – 14 settings

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I read it FIRST!!! HA! Beat you all to it! See my comments later tonight DaveJ!

PM'ed you too...

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You had mentioned once before about using a different manufacturer's bottoming cones? Maybe Pro-Circuit? I have tried to find some info to no avail?

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Awesome Dave!!! Very interesting. I hope all the work and $$ you went through figureing this out pays off in the long run. If only you could of had this dialed in the late '90's you'd be a $$$$ionair!!!:mad:

doc

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Awesome Dave!!! Very interesting. I hope all the work and $$ you went through figureing this out pays off in the long run. If only you could of had this dialed in the late '90's you'd be a $$$$ionair!!!:mad:

doc

yep...at this point it's like puttin lipstick on a pig...:mad:

Maybe he can sell the design to WP for their woods forks? It wouldn't take much to do it to them as they allready have a bottoming cone system.

:mad:

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yep...at this point it's like puttin lipstick on a pig...:mad:

Maybe he can sell the design to WP for their woods forks? It wouldn't take much to do it to them as they allready have a bottoming cone system.

:mad:

Wow, dude, you're brutal. NO ONE else is doing it this way that I've read/seen/heard, not Ohlins, not KYB, not SHowa, not anyone...this is the most complex form of cartridge fork pressure regulation that exists out there. If you can provide an example of somethign with more tunability and fewer parts to fail/wear out/ etc please furnish it or forever eat your words.

Constructive comments and criticism is what DaveJ is after I think.

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Dave,

Iv'e been studying this design very very closely over the past while and am drooling at the thought of all that speed control and backfill cavitation eliminating nirvana that you have materialized.

Is it possible to fit the blow off's and backfill cv eliminator to my ex cannondale ohlins 46mm forks?? on roots and such they beat me up something terrible and I know they have no ultra high speed blow off (only the very latest have that I believe). I don't think I need the hydro bottoming cones as I'm not one for extreme jumping (DR 650).

Thanks for the great insite, It's finally made me quite confident to go and rip my forks apart and actually know what each pieces limitations are:thumbsup: :mad:

Cheers,

Dylan

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Maybe he can sell the design to WP for their woods forks?

don't think so. WP is too ignorant to accept any input from the outside

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Dave looks good, curious though from reading the spec sheet that the BV HS blow off spring and the MV blow off spring are the same rate (318 lbs/in). Why not have one be siffer than the other to get a more progressive curve?

Just to make sure i understand correctly you don't have an isolated fork design anymore, these forks do both rebound and compression damping. Any reason why you gave up on that design?

Good work and I may just have to start moding my extra internals to do something similar, heck I got a few short springs around from when I was playing with the idea of a HS blow off on the BV..

Excellent work!

Tom

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Dave looks good, curious though from reading the spec sheet that the BV HS blow off spring and the MV blow off spring are the same rate (318 lbs/in). Why not have one be siffer than the other to get a more progressive curve?

I think they might blow off at different times as a result of different face shim diameters(areas), AND the flows required by one valve versus the other(MV flows ~3x the oil that the BV does, always), as well as differences in the port sizes >> meaning the psi on say, the MV shimstack would build much faster than on the BV, so It would blow off first. DaveJ, Your input?

DaveJ-

Since this is no longer an isolated design, and the rebound clickers are intact, aren't they also the bleed adjustment around the MV as in the stock configuration? What are your opinions on this? Why not design a small ball check valve into the MV stems you have engineered to prevent the rebound setting from complicatiing the compression bleed around the oh-so-critical MV?

Are you still dishing the pistons to preload the shimstacks?

What are your thoughts on running progressively wound springs in this fork design?

Some clarification: the 10mm OD sleeve (that the shims/solid plate/shim push plate slide on) meets the face of the piston, correct?

TO echo everyone else, outstanding work, Dave...do you do this stuff in your spare time or what?

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Wow, dude, you're brutal. NO ONE else is doing it this way that I've read/seen/heard, not Ohlins, not KYB, not SHowa, not anyone...this is the most complex form of cartridge fork pressure regulation that exists out there. If you can provide an example of something with more tun-ability and fewer parts to fail/wear out/ etc please furnish it or forever eat your words.

Constructive comments and criticism is what DaveJ is after I think.

Sorry, I was trying to be funny and apparently failed :mad: :mad:

While I agree COMPLETELY that it is an amazing job of re-engineering a flawed system it's like figuring out how to make the heater work better on a 1967 Chevy Corvair...if he had done this to the WP 4860 OR Marzocchi 45mm Shiver that are STILL in production then it would have made more sense...guess you "fix" the one that's broke first and then adapt the design to the others as they "need" less?

It is some nice looking work and I may well steal some ideas. Finally have a spare set of 06 WP's to work with!

I meant :mad: DaveJ the scientist no disrespect!

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Also, wouldnt it be sweet if you could adjust the preload on the BV blowoff spring from the outside? even sweeter would be adjustable preload on BOTH the BV and MV.

The problem with too many adjustments is that most people don't know how to use them...

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yep...at this point it's like puttin lipstick on a pig...:mad: Maybe he can sell the design to WP for their woods forks? It wouldn't take much to do it to them as they allready have a bottoming cone system.

:mad:

Awesome Dave!!! Very interesting. I hope all the work and $$ you went through figureing this out pays off in the long run. If only you could of had this dialed in the late '90's you'd be a $$$$ionair!!!:mad: doc

Ever see these guys that sink $15,000 into a Honda Civic so that they can get it to go from 0 to 60 in 4 seconds? After all that work and money, they are still driving a Honda Civic. But then again, they have a Honda Civic that does from 0 to 60 in 4 seconds.

I guess I would have to say it’s worth it if you learn stuff along the way that can be applied into bigger and greater things, and if it keeps you thinking…which is good.

So I agree, there’s a make-up on a pig thing going on here. However, it’s an original and it’s just a platform. The numbers that went into this could be moved over to just about any fork.

Lastly there’s no monetary indent here other than to wow people that are little burnt out on the feel of their ride, or those that can’t get the fork to meet their needs using conventional means.

I’m just here to make it interesting.

(which doesn’t mean that I won’t do something with it if I see the chance) :worthy:

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Dave from you testing how does the front end settle into turns? I remember talking in the past how the zero float MV tends to make the front ride high in the stroke and make cornering different. At the time you were not having a bleed circuit and we talked a little how you can control it with the bleed, both rebound and compression bleeds. That being said now the shim stacks become more critical correct?

Looks like I'm not going to get a lot done at work today, least not a lot of work I'm suppose to do!

Tom

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Also, wouldnt it be sweet if you could adjust the preload on the BV blowoff spring from the outside? even sweeter would be adjustable preload on BOTH the BV and MV.

The problem with too many adjustments is that most people don't know how to use them...

Yes and no. Once they are set there is no need to change them unless you change the stack. Then they have to be re-merged so there is none of the hydrualic gap thing I mentioned.

And yes I agree, simple solutions seem to be what people prefer and like.

You had mentioned once before about using a different manufacturer's bottoming cones? Maybe Pro-Circuit? I have tried to find some info to no avail?

The Factory Connection cones that I’ve seen in the past were exactly like the C-Cycle cones, (which is now RSP). I’m under the impression that the guy that develop them is not related to either company, although I think he may have been tied to C-Cycle in the past. In other words, I was never able to find anyone that had the rights to them and I certainly can’t find any patents on them other than what Showa and KYB have for end of stroke technologies.

I’ve purchased about 20 pairs from RSP and the owner is giving me a good price on them, but lately I’ve had to make so many modifications that it’s starting to make more sense to make them myself. I don’t think that’s cool to do to him, particularly given how good he’s been to me so perhaps I can arrange something. Let me know if you need some blanks (so to speak) and I’ll send some over at my cost.

Dave,

Iv'e been studying this design very very closely over the past while and am drooling at the thought of all that speed control and backfill cavitation eliminating nirvana that you have materialized.

Is it possible to fit the blow off's and backfill cv eliminator to my ex cannondale ohlins 46mm forks?? on roots and such they beat me up something terrible and I know they have no ultra high speed blow off (only the very latest have that I believe). I don't think I need the hydro bottoming cones as I'm not one for extreme jumping (DR 650).

Thanks for the great insite, It's finally made me quite confident to go and rip my forks apart and actually know what each pieces limitations are:thumbsup: :mad:

Cheers,

Dylan

Hey Dylan,

I don’t have any information on the Cannondale forks so I’m not sure how easy a similar design would be. Anything is possible but I don’t think you would want to pay the price for a one-off build.

And the cones are not just for jumping, as I’m sure you have been able to bottom out your forks on a regular basis. I like to think to think of them as medical insurance.

Dave looks good, curious though from reading the spec sheet that the BV HS blow off spring and the MV blow off spring are the same rate (318 lbs/in). Why not have one be siffer than the other to get a more progressive curve?

Just to make sure i understand correctly you don't have an isolated fork design anymore, these forks do both rebound and compression damping. Any reason why you gave up on that design?

Good work and I may just have to start moding my extra internals to do something similar, heck I got a few short springs around from when I was playing with the idea of a HS blow off on the BV..

Excellent work!

Tom

Hey Tom,

I had different springs going for a while, in fact you’ll see this in the charts and photos, but ended up concluding with one spring rate since the option to dial them in via the shims seems to work well.

As for the IDF I’m no longer using it - this design is better. However, the isolated stuff sure has its benefits.

BTW – I also found that you have to run blow-offs on both the mid and base. One or the other doesn’t cut it.

I think they might blow off at different times as a result of different face shim diameters(areas), AND the flows required by one valve versus the other(MV flows ~3x the oil that the BV does, always), as well as differences in the port sizes >> meaning the psi on say, the MV shimstack would build much faster than on the BV, so It would blow off first. DaveJ, Your input?

You’re right. The fix is to run the same spring but at different pre-loads.

Since this is no longer an isolated design, and the rebound clickers are intact, aren't they also the bleed adjustment around the MV as in the stock configuration? What are your opinions on this? Why not design a small ball check valve into the MV stems you have engineered to prevent the rebound setting from complicatiing the compression bleed around the oh-so-critical MV?

Same thing (fault) as with the factory design…and nearly all forks and shocks. So yes, I guess a ball valve or something would be cool. But I have a stack configuration on the rebound that allows the valve to stay fairly closed so it’s not too big of a deal.

Are you still dishing the pistons to preload the shimstacks?
To keep things simple I am not. It’s a lot of work with little benefit, but it does make a difference. Lastly, there’s not much sense in this unless you shut down the by-pass circuits.
What are your thoughts on running progressively wound springs in this fork design?
Ummm…that is what I am running. Did you mean non-progressive?
Some clarification: the 10mm OD sleeve (that the shims/solid plate/shim push plate slide on) meets the face of the piston, correct?

Yep! I also polish them really well. For the base you have to make sure that the edge is sharp as well so that the shim doesn’t catch on it.

Dave from your testing how does the front end settle into turns? I remember talking in the past how the zero float MV tends to make the front ride high in the stroke and make cornering different. At the time you were not having a bleed circuit and we talked a little how you can control it with the bleed, both rebound and compression bleeds. That being said now the shim stacks become more critical correct?

Looks like I'm not going to get a lot done at work today, least not a lot of work I'm suppose to do!

Tom

On the three sets I built up I’m running single stage and very linear stacks so the forks do stand a bit more at the ready than most forks and perhaps a bit more than what most woods riders may prefer. However, that’s a good position to be in when it comes to big jumps, whoops and hitting certain things really fast.

If you raise the fork up in the clamps and keep the oil level low, the bike seems to sit extremely well in the corners. In fact even though they feel high, they still seem to settle much better than all the factory forks I attempted to get to behave.

So yes, if you shut down the by-pass circuits you have to develop the stacks to manage dive and that gets tricky particularly when you want to provide the user with some adjustability.

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Dave, I think your next project needs to be a cure for cancer. I believe you could have this handeled by the end of 2007.

I love the looks of the pieces you made. I woudl love to have a kit , under glass, to hang over the fireplace. BEAUTIFUL!

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Dave, I think your next project needs to be a cure for cancer. I believe you could have this handeled by the end of 2007.

I love the looks of the pieces you made. I woudl love to have a kit , under glass, to hang over the fireplace. BEAUTIFUL!

2nd that........:mad:

doc

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Dave from you testing how does the front end settle into turns? I remember talking in the past how the zero float MV tends to make the front ride high in the stroke and make cornering different. At the time you were not having a bleed circuit and we talked a little how you can control it with the bleed, both rebound and compression bleeds. That being said now the shim stacks become more critical correct?

Looks like I'm not going to get a lot done at work today, least not a lot of work I'm suppose to do!

Tom

Interesting comments on zero float mid valves! I have worked on 2 different sets of forks set up for use in Supercross both had zero float in the mid valve, also mid valve was set up very stiff but included a cross over. Base valving also set up very stiff! Both these sets of forks were very, very plush in first 2-3 inches and very progressive and stiff thereafter.

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Interesting comments on zero float mid valves! I have worked on 2 different sets of forks set up for use in Supercross both had zero float in the mid valve, also mid valve was set up very stiff but included a cross over. Base valving also set up very stiff! Both these sets of forks were very, very plush in first 2-3 inches and very progressive and stiff thereafter.

Did the pistons/valves have bleed holes in them?

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Pistons were stock!

Forks were WP SXS Twin Chamber (similar to 07 SX) and Showas from CRF450F 06.

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