Fork shim stack styles

[bclapham]

scott, hold up a minute, i am only guessing so its the blind leadng the blind i am affraid. lets see what the experts say!;)

 

[JohnScott]

You're right, I actually understood your explanation - when an expert explains I can't understand it - you must be wrong :D

 

[JTT]

Scott, I think you are referring to a cross over shim. If you use a cross over the shims above it will bend over it's diameter, untill the hit the next shims in line. Now, if you remove it, the shim is now supported over a greater diameter and is therefore stiffer. Basically, leverage in increased. Think of it as a lever arm pivoting off the shim below it.

In your example of removing the 16, you would effectively be increasing the leverage, by making the 18 now bend over the shorter 14, instead of the 16 previous. If you were to remove the 12 from the bottom, this would increase the entire stack, as all would now have to bend over the 14. Make any sense? :think:

Ben, with your example, if I understand you correctly, adding a 12 crossover would make the LSC much softer, as the 24s and 22s now will be bending over a 12 (long lever arm). Once they bend far enough, they will contact the 20 and there bending will be now limited by the effect of the remaining shims (they now have to bend too in order to flow more).

I like to think of it like Marcus's analogy of a leaf spring. It helps to put it in better order in my head. Each shim in the stack must bend over the one below it. The greater the difference in diameter, the softer the spring will be (assuming thickness is equal).

 

[marcusgunby]

Sorry its not that simple:( JTT you wrote yours as i was writing this so the not that simple comment doesnt apply to you:)

 


first scott mentioned the removal of a shim making it stiffer.This is only when we talk about the clamp shim(last shim)this sets up the stiffness of the whole stack above it.
eg if you remove the 12 and replace with a 13mm shim the whole stack above will be stiffer.

If you remove a shim in the middle of the stack, the stiffness is overall less in LSC and total HSC.Total HSC is the sum of all the shims stiffness.So of you remove any shims you make total HSC less.Even if its one of the 24mm shims.Thats the whole problem with shim stacks-any changes tend to change the LSC and HSC when you might not want to.A 2 stage stack makes things a little simpler as it to some degree, separates LSC and HSC.However even different size cross overs change LSC/HSC.

Bruce a tip for you :)-if you put in a 12mm shim in your example it will give a soft LSC and will probably blow through the travel.When you include a cross over ,the stack above it becomes alot softer as its pivoting on a small cross over shim instead of the tapered stack it previously sat on top of.Also shim deflections come into play as jer mentioned in a previous post-when you put in a cross over the top stack has to deflect and it will only deflect so far-so if we put in a really thick cross over, the shims may deflect enough to hit the lower stack but will it put any real force on the lower stack?ie will we make the HSC stack almost redundant.

See how instead of getting answers we end up with just more questions.
This is why im using single stage stacks-i accept if i need more LSC i will get more HSC in the end, but im not convinced changing different parts of stack really alters the speed range we hope for anyway.

This is my interpretation and im not saying by a long shot its 100% correct.In the end its all about testing as theorys only work well in a classroom, ask jer about pds theorys and how they pan out in real life;)

 

[bclapham]

so given my example, if you wanted to just add HSC and take advantage of the 2 stage stack, then you would add a few more 24.1 shims, then the crossover (which would give a net effect of a similar amount of LSC, the lord giveth and the lord taketh away type thing) and then add yet more shims after the crossover to add more HSC?

wow, that gets complex real quick. so going back to the single stage basevalve

24.1(5)
22.1
20.1
18.1
16.1
14.1
12.25(clamp)

what would we change to keep the LSC similar, but add HSC? and please dont say "what do you think?":p

 

[marcusgunby]

Right i have some more stuff for you lurkers(i can see you you know)
We speak of LSC and HSC and these are valid terms.However on a stack where is the LSC part and where the HSC part?? even on a 2 stage stack it isnt clear-why?? well if we have a really soft LSC stack it will blow open easily and the HSC stack(at least what we call the HSC part of the stack)will come into play at low fork speeds.So the labelling of the parts of the stack isnt easy to pin down.Also even a stack with no taper to its shape has HSC stiffness.

Any thoughts??

 

[marcusgunby]

bruce its real hard;)
maybe make the clamp shim bigger but reduce the no of 24mm shims??

 

[bclapham]

Originally posted by marcusgunby
However on a stack where is the LSC part and where the HSC part?? even on a 2 stage stack it isnt clear-why??

what do you think?

so, in terms of the basevalve i listed, talking about the bigger rider, then one option would be

24.1(3)
22.1
20.1
18.1
16.1
14.1
13.25

what do you think?

 

[KTM-Lew]

Bruce......I would remove one 24 and add a 13 between the clamp and the 14.


Guess we posted at the same time. :)

 

[marcusgunby]

What i think we need is a shim stack program:)

does anyone know of one we can get for a reasonable price:yeehaw:

 

[marcusgunby]

BTW all this talk of single stage stacks goes out the window when we go onto shocks-i have never tried a single stage stack on a shock(apart from a WP PDS and that doesnt count as it was terrible with any stacks)

 

[jeffro847]

I love this topic I started!
Its getting more complex and confusing with each additional post!
I love it!!!!!
I'll have to see what I think after I play with my own valving here in a week or two.
I ordered a bunch of shims of different diameters and a few of different thiknesses...
So I'll have plenty of options to "mess" with, or "mess up" with! Ha ha!
That sample shim program on the suspension network site gave me more ideas or clue's as to what adding shims to different places in your stack does to affect dampening in the entire range.

 

[marcusgunby]

Kevin in previous discussions, it was talked about 2 stage stacks having dead spots , as the stages cross over-any thoughts on this?Also do you feel if we can get the 2 stage stack to do most things, the single stage is redundant?

 

[KTM-Lew]

So Marcus.....would the mid-valve, if properly set-up, fill-in the dead spots.... :yeehaw:

 

[bclapham]

or maybe using a non independant crossover?:p

 

[KTM-Lew]

My question....is non-independant even a word....wouldn't dependant and independant have opposite meaning's? You don't need the non.....? :p :flame:

Kinda sounds like army intelligence or some other misnomer. :scream:

Seriously, are you talking about (non-independant) using a shim with a large inside dia (shock shim/ 14-18mm hole) and a fork shim of the same outside dia to fill the hole. Allows the stack above it to pivot easier but maybe doesn't have the "dead" spot?

 

[marcusgunby]

KTM lew you are speaking of a preloaded shim-not the same as a non-independant shim.

As for dead spots i dont even know if they exist -trouble is without a dyno its mostly thoerys that are hard to prove/disprove.