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Discussion Starter · #1 ·
Hi there,

Looking for a little explanation on the shim stack itself in general what they do and then also the roco in particular,


Any reccomendations in which order to setup the shims?



PS, I ride a Commencal Supreme.


Cheers,
Jam.
 

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Shims control damping. Basically the shims flex to allow oil to move through the damper, and do so to varying degrees depending on how big a hit the rear wheel takes. Basically there's a piston with some holes in it, and the shims cover up the holes. When you put some force into the shock, the damper shaft tries to build up pressure in the damper oil, and the shims flex to allow the oil to pass through the piston, relieving the pressure.


If you don't know what you're doing, and don't have specific tuning goals for the shock, I wouldn't mess with the shim stack. If you've got specific things that you'd like to change about the shock's performance, then you can consider whether or not messign with the shims is a good way to address them.
 

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Discussion Starter · #3 ·
cheers for the reply,

I've taken the shock apart several times, and I had a rough knowledge of what they done, just wanted a bit more clarification of things.


I know what I want, and what I'm looking at in the shock, and I want to achieve a some more small bump compliance, as on my commencal it already pedals and carries speed extremely well. So I'm thinking of making more use of the back end and softening it up a bit.

Any reccomendations for which to move to where?


cheers,
Jam
 

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Shimmed damper adjustments are a 'black art' that is the people who know how to do this stuff well, know it from trial nad error, not from a formula or calculation...Ther are also many many parameters to consider....shim thickness, shim material, shim diameter, shim pre-load, and then lastly the actual shim configuration on any particular piston.

Tha being said, there are some general ideas.....the shims that are closes to the piston (and any preload) have more effect on low speed damping. The shims that are further away from the piston have more effect on higher speed damping. You are quite limited with only having the stock shims as your only option is to change the arangement of what you have (you need to keep the total shim stack thickness the same).

You need to get a better understanding and explination of what you want to change and if that change involves more high speed or low speed damping..where speed is in reference to the shock shaft. 'Small bumps' does not define the damping used. High speed breaking bumps would be high speed damping....small 'rollers' undulations especially at lower trail speeds would be lower speed damping. Low speed damping also controlls chassis movement and pedal input.

Get a better idea of whether you want to lowe LSC or HSC or both..and you whoudl be able to make some small changes to help.
 

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Discussion Starter · #8 ·
Marcolino said:
if you hit the search function i think you´ll find some uk site with the manual online

search for roco wc...
Yea the website is Windwave, the UK importer and its just a Service manual mate, Nothing in detail about what the actual shim stacks do, Cheers anyway.

Fsr, not seen that, and I've done a ton of searching on several forums and google, but if you do pass it on

Davep, Cheers man,
I done some rough drawings of the shock n compression/rebound assembly (nothing special) and I know I wanted some more low speed damping, as the roco ramps up enough on the Commencal and pedalling is also great.

I have changed the Shim stack slightly, from the sort of triangle shape to a sort of a narrow christmas tree shape, after thinking about this it sorta worked, and Yea, I could do with some more shims actually but I'm gonna play with what I got.

Can you guess the damping of this? Dave? quite a guess eh?

cheers everyone and anyone once again
 

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"El Whatever"
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jammac said:
Yea the website is Windwave, the UK importer and its just a Service manual mate, Nothing in detail about what the actual shim stacks do, Cheers anyway.

Fsr, not seen that, and I've done a ton of searching on several forums and google, but if you do pass it on

Davep, Cheers man,
I done some rough drawings of the shock n compression/rebound assembly (nothing special) and I know I wanted some more low speed damping, as the roco ramps up enough on the Commencal and pedalling is also great.

I have changed the Shim stack slightly, from the sort of triangle shape to a sort of a narrow christmas tree shape, after thinking about this it sorta worked, and Yea, I could do with some more shims actually but I'm gonna play with what I got.

Can you guess the damping of this? Dave? quite a guess eh?

cheers everyone and anyone once again
Make a search for "shim" by user Dougal. He made a very thorough explanation of it a while ago.

Basically, a square shape shim stack provides low LS damping and higher HS damping.

A conical shape stack, gives more LS damping and less HS damping. It's digressive and helps to have slightly more travel or a more linear feel.

There are several parameters to play with.

IFP depth helps control the progression and bottom out. The smaller the chamber, the higher the ramp up and viceversa.

IFP pressures is a second parameter to control progression and damping to a much lesser extent. It helps prevent cavitation too.

Then you have oil weight... which is kinda obvious.

The dishing of the piston plays a part too along with preload on the shim stack... more dish and preload give more low speed damping but a more digressive feel. Not to mention the shape and size of the orifices in the pistons. But for your case, I'd just consider them a fixed parameter and not give it much thought.

Then you have multi stage stacks (combination of square and conical stacks). Actually, in a piggy back Roco (except TST) you have four stacks... main piston compression, piggy back compression stack, low speed rebound and high speed rebound.

That is why HAB is asking what are your goals. It may be better to start from there. It may help you to understand better how tuning goes.
 

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paging Tom Rogers! Tom told me that to gain more small bump compliance if you don't want the stock mild platform tune, remove the single compression side shim from the main piston. Compression adjust still works. I don't own a Roco WC (I wish! but my PUSH'd Vanilla RC is working just fine thank you Darren! but I wish I could change the oil in my shock like the WC allows without busting into the RC and fitting a schrader valve).
 
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