KTM Shim Question

[Layton]

Maybe one of you suspension pros can help me out.

A friend of mine has a Y2K 300 EXC. In an effort to soften the suspension when hitting smaller rocks, etc. he removed the base valve (the one on the bottom of the forks) and then removed every other shim (I think there were about 18 to start with) from the stack. He claims that this will soften the fork on the slow speed side but that it will still react ok when hitting bigger bumps at speed

I don’t have enough knowledge in this area to know if he is correct or not. How about it, what exactly will this modification do?

 

[GlennP]

I'm no expert, but from what I've learned messing with my WPs lately, this will probably soften everything up. Also, rock hits cause high fork speeds, which is controlled by high speed damping. What will also help (works great in mine), is removing all but one midvalve shim (required to seal rebound piston).

 

[Layton]

Glenn,

Thanks for your reply. Looks like it will just make the fork softer through out the stroke.

I was really hopeing that a few more people would comment just to get some other opinions. You must have got it right or a few more would have jumped in. :)

 

[marcusgunby]

Taking out that many shims will make a huge difference to the action LSC and HSC.

 

[Layton]

If you only wanted to soften the LSC would removing less shims accomplish that or would it soften both the LSC and HSC only at a lesser amount?

 

[JTT]

If you only want to effect LCS, remove shims closest to the piston. The shims above these first ones will effect everything below them.

Keep in mind, I am no expert ;)

 

[marcusgunby]

JTT has it right.

 

[GlennP]

Scrap the midvalve! It makes the fork action much better (for woods work anyway). In my experience, you can then tune the LSC stiffer without intoducing harshness.

 

[JTT]

oh, oh! I hear Jer's response coming....something about medieval torture... :scream:

 

[GlennP]

I'm no expert either, but the guy who advised/did this mod is. I can't argue with success. The fork feels much more comfortable hitting sharp edges, without altering the base valving. For moto/whoops its probably best left alone.

 

[Layton]

Sorry for not getting back to this post quicker. I am out of town on vacation and could not get to a computer until today.

JTT or others,
I do only want to change the LSC. I am trying to picture this in my mind, as I don’t even have the parts book with me at this time. In the base valve would the shims closest to the piston be the larger diameter ones in the stack of shims? If that were the case, about how many shims would you remove?

I realize that this is why people pay good money to suspension shops but I would like to play with mine some and need a starting point. I like the suspension but after riding several pre-2000 models (KTM’s) I realize that mine is much stiffer at low trail speeds on rough ground. No matter how far I back off the compression, the fork is still stiffer on the slow stuff than what I would like. What I want to do is make mine smoother like the earlier forks but yet retain the great suspension that I have at higher trail speeds.
It is the LSC that controls this isn’t it?

Also, would 2.5 weight fork oil help this? I currently have 5 weight in it.

 

[JTT]

Layton, yes, I was referring to the larger shims closest to the piston. As far as number to remove....trial and error...make little changes at a time and document results.

I doubt you will have much success with the lighter oil, but it is an easy change :D .

As far as what you are trying to accomplish, you must try to think of your suspension in terms of speed that suspension is moving up and down, not trail speed. Try to think about the particular area you are having problems...now, is the suspension forced to move quickly? or is it a very slow movement? Try to think of the bump in terms of distance the suspension has to deflect vs. the time it has to accomplish this (relative to forward speed and steepness of ramp, or bump face).

In my experience, most "harshness" people feel, with MXers in particular, on trails is usually not a LSC issue, usually actually the faster ranges that are the problems.

Do a search for "shim shuffle" (part 1, 2 &3). THis thread when on for some time (and actually 3 threads) and talks about some of the issues you are asking about. It might help clarify some.

Your problem may also be spring related too...

 

[Jaybird]

I'm just a suspension newbie, but I would think that the spring rate issue would need to be addressed before anything else. I would think you would just be running endless circles if the spring rate for your weight is not proper.
Does this sound right?
The more I read about problems folks have with suspensions, the more I'm convinced that Ross Maeda is on to something with his Enzo Sub-tanks which in theory, allow the forks to operate normally(soft) under slow speeds and maintain stiffness for high speed. Like being able to change oil height "on the fly" so to speak.

 

[JTT]

Jaybird is right about the spring thing. That's why I mentioned it (although should have been less candid). Springs are the foundation of your suspension and should be the first area of attention.