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CRF250X & R and CRF450X and R forks

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Hi, I was lurking around here looking at the CR80 fork swap for the CRF230F frame as I have a project bike I'm working on. I noticed some of you are putting the full sized CRF250 and 450 forks on these bikes. I know those forks well.. the 2004-2009 models. To get them to work you'll have to really lighten up the valving, springs, ICS springs etc. go to zero on preload. 

And, those particular forks have a very restrictive stock mid valve setup. You're going to want to do some work on that.... as in way looser on the compression setup and different parts will help there even more. 

If you folks are interested I can send you some info... I have pictures that can help explain some of the issues... you'll want the softest ICS springs you can get too. 

Let me know the level of interest. 

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One of the first things you'll want to do is address the midvalve. Note the photo below. The bright al "spring collar" that the mid valve compression stack sits on top of is a much larger diameter then the one below in gold on the RaceTech midvalve assembly. This larger spring collar is a major reason for the harshness you feel on that fork when hitting sharp edge bumps. So, you have to address this to get a "plusher" ride. 59b4d4e0e3893_Midvalvesonrod1.JPG.f3b2936a2830de4e64841244fffdcfd1.JPG

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On your left in the pic below is the honda midvalve piston. In the middle is the midvalve piston from a SUZ RMZ250. Also a showa fork. On the right is the racetech midvalve piston. Look how much taller the RMZ one is. How much more oil can flow into the holes that feed the compression side of the mid valve. The RaceTech one isn't bad... better than the Honda one. But that RMZ piston flows more then either by a long shot. If you combine the RMZ piston with the RaceTech smaller spring collar you have the most flow in the mid valve area.... The RaceTech one is better than stock for sure. Lot of the RT flow comes from that smaller spring collar - smaller Diameter which allows much more flex of the stack that sits above it. 59b4d5e700960_MidvalveHonvssuz.JPG.212a78a58c9af5586bf2c21d5abc778a.JPG

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Here are some other pic's from a different angle. See how much smaller in Diameter the RT spring collar is? 

Midvalve SUZ vs Race.JPG

Midvalve side 3.JPG

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Ok... now look at the RT piston on the right. You see how you can see some gold below the shim stack? RT uses a smaller diameter shim stack face shim for the rebound stack. That smaller shim allow oil to go around it in the cartridge to access the compression part of the piston. ON the left... you see how there is less of the "black" part of the piston that you can see? The face shim on the rebound side of the stock honda is larger... which lets less oil by it into the compression stack. 

 

Make sense how the one on the right lets more oil by? The other dim is the height of the area that you can see in the pic's above.  

Comments?? Questions?59b4d77ee503f_SmallerDiashimstack.JPG.e0140b6aa53e0e202796e78af181f3e6.JPG

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So now you get how they get more oil to below... before we even talk about valving. But, in stock form, that Honda midvalve is the source of lot's of trail harshness. 

So you want to address that. A RT kit is actually valuable in this instance. For the midvale. You don't need it for the base valve. However, the base valve and ICS spring rate need to be reduced.

Further, there is a secondary stack of shims behind that fat thick washer under the base valve. It;s between that fat washer and the o-ring you see in the photo below. You want to soften that a bunch. There is a face shim on it too. You want leave one face shim on it then flip that stack upside down so the smallest washer is now against the face shim. Put it back together after flipping it upside down. It will look like a Xmass tree upside down with the face shim at the bottom of the tree. 

Make sense? You'll have to take the assembly apart to replace that ICS spring. The stock one is too stiff... this hurts the small bump absorption. So put in a much softer one. 

 IMG_1769.thumb.JPG.1de7b8f0841a26120095c5de1dae789f.JPG

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9 hours ago, PT564 said:

So now you get how they get more oil to below... before we even talk about valving. But, in stock form, that Honda midvalve is the source of lot's of trail harshness.

Interesting material, thanks for sharing. This confirms what I've read before about shocks for high-velocity (racing) vs. trail riding. I have added a link back to this post here, under "Zone 5" options, down towards the end: http://bit.ly/2wQfpeH

Edited by RedMesa
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My weight is 170 wet, probably 180 with gear.
Interesting info. I've gotten my "R" forks pretty good as far as harshness but they are mushy because of the soft valving and not good in whoops.   I softened the bleed stack but I'll try using a single face shim. I only fill the cartridge to the ledge and this reduces pressure on the cartridge fluid from the ICS spring, but a softer ICS spring would prob be better. I went a bit extreme on my last revalve to see what effect it would have and I would characterize the mid and base compression stack arrangements as more of desperation to reduce harshness than good for chassis control (a bit floaty) so I need to tighten them up a bit.  Improving mid valve flow seems a logical way to reduce harshness and would allow firmer valving for better chassis control. 
My current  point of reference is a light weight XR218 with CRF150R forks running Gold Valves.

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Chuck - what spring do you have in that fork? 

And what is your spring preload set at? I would recc a 41Kg spring in that fork for your weight for trail riding. I've tried 45's, 44's, 43's and finally a 41. The 41 was the best.. My midvale compression damping is very light. Oil is set by CC's. I'm at 380 CC's of oil in the outer tube. I use 5 wt fork oil. 

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Open up the midvalve. Take out the 17's ... all of them. Leave 1 of the 15's in. Pull the float shims out so it has full float. That mid sucks on that fork. The stock one. The spring collar on that mid is too big... to big a diameter. Very restrictive. 

Now, have you checked the preload after shorting it? Do you know how to? Kinda hard to describe in words which is why I ask. You want zero preload on that spring for trail riding. You want to get that fork to move in the little stuff. You can add preload in later to hold it up if that is a problem... but with that spring..you should be find. Unless you shortened the spring?  

 

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20 hours ago, PT564 said:

Hi, I was lurking around here looking at the CR80 fork swap for the CRF230F frame as I have a project bike I'm working on. I noticed some of you are putting the full sized CRF250 and 450 forks on these bikes. I know those forks well.. the 2004-2009 models. To get them to work you'll have to really lighten up the valving, springs, ICS springs etc. go to zero on preload. 

And, those particular forks have a very restrictive stock mid valve setup. You're going to want to do some work on that.... as in way looser on the compression setup and different parts will help there even more. 

If you folks are interested I can send you some info... I have pictures that can help explain some of the issues... you'll want the softest ICS springs you can get too. 

Let me know the level of interest. 

 

2 hours ago, PT564 said:

Open up the midvalve. Take out the 17's ... all of them. Leave 1 of the 15's in. Pull the float shims out so it has full float. That mid sucks on that fork. The stock one. The spring collar on that mid is too big... to big a diameter. Very restrictive. 

Now, have you checked the preload after shorting it? Do you know how to? Kinda hard to describe in words which is why I ask. You want zero preload on that spring for trail riding. You want to get that fork to move in the little stuff. You can add preload in later to hold it up if that is a problem... but with that spring..you should be find. Unless you shortened the spring?  

 

NOW YOU SHOW UP WITH ALL OF THIS DEVINE PLUSHNESS GUIDANCE! :)

So clearly this will allow for more oil movement and plushness but how will all of this effect control? 

I have a fresh set of 2006 CRF250R forks ready to install on my 230F which I revalved with the help of this site and the steady patient guidance of Motrock93B.

My mid-valve compression stack is:

20 x 2 ,  8 mm ID (floating)

17 x 4 ,  8mm ID (floating)

10 x .2mm x 6 mm id x 2 (non-floating)

13 (non-floating)

12 (non-floating)

Float. .35 mm

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  The float is really has a big effect on these forks. To check it measure the thickness of the piston and the collar the shims float on with them held together. Then move over off the collar onto the shims that float. The difference is your float. For supercross they clamp the shims down tight, zero float. For MX normal is .15 to .25mm (stock is .20-.25). For the woods even more float. The mid-valve is always moving when the fork is. The base valve functions as the damper rod displaces oil into the upper chamber. More float allows the fork to move more/faster before the oil flow increases enough to begin deflecting the mid-valve's compression shims. I've never compared mid-valve pistons before but, after looking at PT564's pictures, it does indeed look like the more restrictive stock pistons could be a negative influence when setting up a bike (especially a CRF230) for the woods. I've got 2 sets of forks for my 05 CRF250R and I've been into them several times looking for better settings. But I ride my CRF250 on the track and it is indeed too firm for the woods.

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  It's been done but it tends to make the forks mushy and dive too deep into the travel too quickly. The base valve has to do all the work if you put a check plate in the compression side of the mid-valve.

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Wow! Lots of significant theory and modification information in this thread. I don't wish to step on toes and simply wish to point out that it's easy to go too soft in our quest for "plush." All of this is very dependent on the speed we ride. Too soft can cause issues when cornering. Since suspension tuning is so personal, I think it's a good idea to begin with the idea you'll likely need to dive in a few times to make additional tweaks as you test ride your mods. This bracketing will help a rider improve suspension action specifically for their needs. It's all a compromise in the end. Personally, I'll live with some low speed firmness in exchange for a plush ride at speed with more feedback and precision. Others will prefer a softer setup.

 

Yes. A softer midvalve helps a lot for woods riding. Removing floating comp shims and increasing float are tried and true mods. For serious re-engineering, consider Smart Performance's completely changed MV. It makes a lot of sense (theoretically) by allowing high suspension velocity hits to "blow off" more than a stock setup. I haven't tried them, but like the idea.

 

On the Base Valve, too soft on the Low Speed stack can make the forks harsher since they will flex easily into the rest of the stack thereby engaging all the shims. This results in much greater hydraulic resistance/harshness when banging into trail trash. Deflection.

 

I've had good results sticking with stock components and adjusting. My X forks work better for me now that I've softened the MV comp (leaving 20s as my face shims to work as intended to direct rebound oil flow through the piston ports), and increased the float a bit. I've left the BV LS stack stock, and softened the HS stack. My bike feels good and gobbles up square edges and trail trash as long as I'm riding quickly. Instead of deflection, my bike feels precise with some "rumbles" as it soaks up the bad stuff. Deep singletrack whoops now deliver slight thuds instead of thwacks as my bike skims them better. Really fun and much safer. If I were to ride slower, more extreme enduro type rock gardens and such I'd soften things more. Right now, my clickers are mid-range and opening them dramatically softens things. So, I'm within clicker range of tuning for various conditions.

 

Why not run softer settings? For me, I lose precision. In corners and picking lines. I lose feedback and the ability to press the front tire firmly into the ground for improved cornering traction. Also, the ride is so good at higher speeds.

 

I don't envy professional tuners trying to get this all "right" for riders after a phone call and questionaire.

 

 

 

 

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So, a couple of things. From what I've seen that SmartPerformance product is midvalve that flows more. Which is a good thing. A bigger piston'd MV will allow you to ad some shims back in if need be without the hydro lock that occurs on the stock piston.

Keep in mind THAT stock honda MV is very restrictive. And the spring collar has a large diameter too..... so restrictive piston with spring collar that blocks stuff too. The same showa forks for the RMZ has a much larger MV piston (taller too). And the KYB SSS forks that people love have the biggest most oil flowing MV piston I've seen. That bigger piston allows you to use the shims more to tune the feel of the forks. 

So, if you're *setting these up for woods* riding, go way soft on the mid valve. I would suggest a RT or even a smartperformace deltaco thing if you like. The stock one will hydro lock on you on sharp edge hits. It's horrible for trails. 

Now, once you get a mid valve that will flow and not "lock up the fork" on sharp hits you can adjust the hold up with spring rates and preload on the spring. Frankly, the best way to tune is to go too soft then add back in valving, spring rate or what have you. But find that too soft point if you can. And make big changes when you are trying to find the right setting initially. Big changes in one direction will tell you if you are going in the right direction. Small changes will be harder to detect. This is advice given to me by a buddy of mine that ran Fox Shocks for many, many years. Once you know the right direction you can then sneak up on the perfect setting for you with smaller changes. 

Also, for me on technical single track I have a 41KG spring in my CRF250R (2005 fork). That along was a very soft MV - it's a gold valve - worked very well. Put that fork it on a CRF230.... I'd probably go with a lighter spring. 

But, first and foremost, for trail riding with this fork, on a CRF230, do yourself a favor and get a RT or SmartP or something.... else for the MV. You really want one that flows? Get the SUZ RMZ250 MV piston from Suspenion Direct and use the raceTech spring collars. That setup would flow a ton of oil. You'd end up building back in a MV stack to control the fork it would flow so much oil. Cheapest way... RT MV for this fork is probably a good starting point. 

 

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