Motoman, EGO, other suspension experts, I have my forks apart need you opinions



33 replies to this topic
  • James_Dean

Posted July 30, 2002 - 01:46 PM

#21

Ben,

Maybe you already know this. The spacing between the low speed and high speed stacks is called the crossover gap. This is the flex distance the low speed shims move before they start to push the high speed shims. It looks uncertain what the gap is set it at in the lists.

The first proposed stack did not show a well defined gap because you're listing (2)x24, 22, 20, 16, 11. It's hard to tell the flex point where the second stage takes effect, .2-.4mm??.(each shim is .1mm thick)

The second proposed LS stack had (4)X24, 22, 14, 12. This still isn't clear, ~.2-3mm?. Was that from the RT charts? If you wanted .2mm crossover gap then use (5)x24, 14, 12.

I would hope you're using listed low speed (CL) stacks to ensure that you don't make it too mushy by extending the low speed range. In other words too big of a crossover gap. If one thing would mess you up with the compression shim stacking, I think that would be it.

James

[ July 30, 2002: Message edited by: James Dean ]

  • motoman393

Posted July 30, 2002 - 02:27 PM

#22

These are the kind of posts I like reading...keep it coming. That video from ccyle is pretty informative.

DaveJ,

your fax is printing right now Thanks man!

Garrett

  • armourbl

Posted July 31, 2002 - 05:33 AM

#23

Ok,

James Dean, you are most certainly correct. The more I study the stack, the more I came to understand what you described myself.

Last night I went to Piper Performance. They are a Race Tech certified shop in Phoenix. They are one of the top Race Tech shops in the country. Cliff the owner was very helpful. He looked over my shim stacks, and said, after a long pause, let me go work up a stack for you. He took my print out and went to the back of his shop after asking some basic questions about me and my riding.

He came back a few minutes later and gave me the stack specs below. No charge.

Low
(3) .15x24
(1) .10x18
High
(1) .15x24
(1) .10x22
(1) .10x18
(1) .10x16
(1) .10x14
(1) .10x13
(1) .10x12
(1) .10x11

Dampening circuit. He said I could use (4) .10x27 and (1) .10x25 to create the check plate to replace the mid-valve. Then he said to pretty much leave the stock dampening shim stack the way it was.

Here is what I came up with for the dampening shim stack.

(3) .10x27
(2) .10x24
(1) .10x20
(1) .10x16
(1) .10x14
(3) .10x11

I'm 190 without gear, 6'1" fit frame. He recommended oil level of 95mm, compression 10 clicks out, dampening 10 clicks out, 6-8 mm of preload. (how exactly to I set preload on the forks?, LOL)

I feel very confident that these stacks, along with the cylinder valve seal, will work very well to improve my WR250F suspension. I've got the forks half way back together now, and the wife is still being patient about oily parts all over her kitchen table. Just need to screw in the base valve assembly, add the oil and close everything up.

I'll let everyone know how the suspension feels.

Next saga will be the Shock, but I'm waiting until after I get back from Crested Butte to attempt that...I'm tired. LOL.

ben

  • BikeDestroyer

Posted July 31, 2002 - 10:17 AM

#24

Ben,

Are you setting up your suspension for Track or Trail or trying to go somewhere inbetween? I am hoping Cliff will have my head ready by friday so I can ride this weekend.

  • armourbl

Posted July 31, 2002 - 10:26 AM

#25

Well, I'm shooting for a happy medium. If it is a little on the appropriately stiff side for the track then I can deal with that on the trail...

I just went over the Race Tech instructions again, and I just found that I may have not chosen a good stack for the rebound circuit. My current stack listed above is a single stage stack. I need to go back tonight and change it to a 2 stage stack with slow and high speed stacks.

Probably set the dampening to:

Low
(3) .10x27
(1) .10x11
High
(2) .10x24
(1) .10x20
(1) .10x16
(1) .10x14
(2) .10x11

  • moto_madman

Posted July 31, 2002 - 10:29 AM

#26

C-cycle does a lot of work for racers around here. They are based in Colchester CT. I bet ya didnt know this:

C-cycle makes professional level down hill and free ride mountain bike forks. They are minature dirt bike forks with 8 inches of travel and they come with tripple clamps. They cost about two grand though.

  • James_Dean

Posted July 31, 2002 - 01:36 PM

#27

Ben,

I haven't spent much time with rebound stacking because stock usually works well enough with the clickers adjustment. When I have added crossover shims to the fork rebound stack, it was to keep the front end up, to ride higher. It was effective at this in both low and high speed situations. Again, the clickers are low speed mostly.

When you are trying to understand rebound damping, keep in mind the high speed damping is only used when the fork has moved deeper in the travel. That is when there is more energy stored in the spring and it returns much faster. Under low deflections (even choppy stuff) the rebound only sees low speed even though the compression side will use both low & high speed.

If you soften the rebound damping with a crossover and soft low speed stack, you may end up needing to turn the rebound clicker in (firmer) to offset it. The adjustment may not be much but keep it in mind.

James

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  • armourbl

Posted July 31, 2002 - 01:46 PM

#28

James Dean,

So are you suggesting I run a bit stiffer low speed stack on the rebound than what I've suggested with the figures above in my earlier post?

Ben

  • James_Dean

Posted July 31, 2002 - 03:40 PM

#29

That is entirely up to you.

You have to compare the setting to where it was at initially and decide what you want. If you think the change needed less low-mid speed rebound, then that is what you're getting. By adding the crossover the high speed stack is further away so it will be affected to a degree also.


The other consideration not mentioned is the diameter of the crossover shim is at 11mm. This crossover diameter is smaller than the 12mm suggested earlier. A smaller diameter here is also acting to soften the shims towards the valve face by making a longer span to the outer edge (27-11)/2=8mm. This is in effect a clamping shim for the low speed stack. A bigger crossover shim diameter of 13 makes the LS stiffer (27-13)/2=7mm. It's like lengthening the span on a diving board to make it flex easier.

My suggestion is to take the advice of one of the Pro's you have talked to about the stack and when you ride it try to feel the effect of what it has done. If it's no big deal pulling the forks apart, then experiment with your own ideas.

James

  • armourbl

Posted July 31, 2002 - 06:53 PM

#30

I think I've got the pulling the forks apart thing down pat. Only draw back is that it is very time consuming.

I completed my stack selection before getting a chance to read your response above, but I think I may have been reading your mind. I went with the below stack for my dampening...

Low
(3) .10x27
(1) .10x12
(1) .10x11
High
(2) .10x24
(1) .10x20
(1) .10x16
(1) .10x14
(1) .10x11

This is actually pretty close to stock if I remember correctly, maybe just slightly more aggressive.

The forks would be back on the bike, but I only had one bottle of fork oil and it wasn't enough. Word to the wise, a fork oil change (one bottle is enough), a full fork rebuild (pick up two bottles of oil). So, one fork leg sits complete, the other sits half done until tomorrow night when I pick up some more oil.

I should have a ride report after this weekend.

For those who seem interested, I will keep posting on this thread as long as I have news to report about the suspension changes.

I haven't been one to contribute a lot to TT. Hopefully, this thread and my experience will show others that you can simply change your shim stacks, with some time and effort, for a moderate improvement in your stock suspension.

ben

  • armourbl

Posted August 02, 2002 - 05:17 AM

#31

Ok,

I got my forks finished last night and mounted them to the bike. I went for a quick ride down the street just to check everything over. I set the compression 10 clicks out and the rebound 10 clicks out.

First impressions are, woa, this is much stiffer than before. I seriously doubt I'll be bottoming like I was before. The bike seems to ride higher too. The closest thing I have for a test is a couple of speed bumps on my street. So no telling how this will perform on the trail or track. I'm doing some trail riding this weekend and will report back when I get back.

ben

  • DaveJ

Posted August 02, 2002 - 07:54 AM

#32

Ben,

You're right, your forks are too stiff.

Usually (not always) a fork that "rides high" will not allow the front end to dive into corners. The bike will push.

Additionally, it’s usually a good sign that the fork is going to be too stiff on the straights.

So of course you can turn out your clicker screws until things drop down and loosen up.

However, it’s a bad process.

Ever since I’m been doing this stuff, the measurement for a suspension setting has been the number of clicks out. Although this is a fine way of noting a setting, it implies a process that we should start at the bottom and work our way out.

What we really should be doing is to approach the damping rate (curve) from the other side, meaning that you should turn all the screws out, then turn them in until you find a minimum setting.

This will lead you into a new dimension of setting a bike up. However, it’s a little confusing when most assume that the sweet spot can be found by entering from either direction.

The next process may help with this.

When making your settings, the rebound should be dialed first. The primary reason for this is that the rebound setting actually has an effect on the damping curve for compression.

Sometimes with certain valve stacks and fork designs, you can add the desired rebound, which will offer up enough compression to where you can leave the compression screws all the way out. It seems crazy, but we always assume that more is better when often it is not.

Now, with rebound set you can then add compression but only as much as necessary.

Lastly, the only reason you will add compression is to dial-in stability. You’ll feel it come in as you add and test ride the bike. In other words, don’t use it as means to deter bottoming, (that's a story in itself).

Try that and let us know how it works out.

DaveJ

[ August 02, 2002: Message edited by: DaveJ ]

  • James_Dean

Posted August 02, 2002 - 08:49 PM

#33

He came back a few minutes later and gave me the stack specs below. No charge.

Low
(3) .15x24
(1) .10x18


---------------

(1) .15x24 shim is roughly equal to (3) .10x24 shims.

A stack of (3) .15x24 shims will be comparable to (9) .10x24 shims . This is the low speed stack but will carry over into the high speed damping also.

The shim stack should explain the change in feel from your original valving. What was the original compression stack?

[ August 03, 2002: Message edited by: James Dean ]

  • armourbl

Posted August 05, 2002 - 02:38 PM

#34

James,

I posted the original figures a few posts up. I tried my best to document these accurately, but may be off a little.

Dave,

I will try what you said. The front could stand to have less compression for the type of trail riding I do. I will back them out to the soft side and move up gradually as you suggest.

Special Note...

The Phoenix area associate for MX Tech rode with our group this past Sunday. He came to help a recent customer get his suspension dialed in. I took the opportunity to have him test out my work. During a few breaks during the ride we discussed what I had done, I gave him the specs, etc. He seemed a little concerned about having removed the mid-valve and a few other things. When we got back to the trucks I asked him to ride the bike and give me the ugly truth if need be. He came back and told me it felt like a professional Race Tech Gold Valve set up. He thought it felt really good actually, especially considering it was my first attempt. He still thinks I should put back the mid-valve stack combined with a softer slow speed compression stage stack.

To me, the suspension felt good. It soaked up everything, even the nasty whoops. About the only negative thing to speak of was something that DaveJ mention in his last post. The front riding higher did make the front have a wash out feeling. I'm at 10 clicks out right now, I will soften the compression more and see what happens. If I need to, I'll just pull the base valve and soften up the compression stack.

I'm riding at Crested Butte, Colorado this weekend. I'll give a ride report about the suspension after I get back.

ben





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