Changes to shim stacks?

What would be the affective difference between these two bv fork stacks?

30 30

28 28

26 26

24 24

22 22

20 20

18 18

16

14

12

Stiffer/Softer?

What does a longer taper do for the feel?

the second is waaaaaay more stiff.

the last shim has enormous effect on the damping curve, because the others have to bent around it.

A straight stack, eg. all 32 shims is more progressive than a tapered one.

But keep in mind that you always change the hole stack. its difficult to alter just LS or HS.

Thanks

So, even though there are less shims, it makes it softer because of the taper?

Edited by gerkom

not the taper.the larger clamp shim(last small shim in the stack,the other shims have to bend over the last shim).larger clamp=stiffer stack.

Aha ... that makes a lot of sense !! Thanks once again to TT members....

So, let's say that you had a 18 shim with a 12 clamp. How would that impact the stiffness/softness? Or is that not realistic?

So, does the taper impact the LS vs HS?

the taper doesn't have a big influence in the stack , the number of face ( biggest) shims and clamp have a huge effect on stiffness , you could remove the whole taper part from most modern kybs and not even notice a change as they have so many face shims , on a stack with few face shims the taper adds up to a good amount of the stack strength , stacks are very hard to judge unless you look at them all day long and test or use a shim program like restackor

So, does the taper impact the LS vs HS?

I also think about that for quiet a long time, because its more or less the key to success!

IMO:

If you clamp your second stack on a 12 shim, it will be softer then your first with the additional 16 and 14 there.

Taper or not... Race tech sus bible says its because of the bending points of the shims.

On a straight stack all shims bent more or less at the same area and that can cause distorted shims.

On a tapered stack the shims bent over more points...

I guess it also depends a bit on the space you got to the base plate.

A straight stack without proper spacer (clamp shims) could hit the base plate and restrict flow through HS movement!

As you may noticed clamp shims are mostly significant thicker than the deflection shims on a stack, to gain space!

TT member kawahama did some tests to show the fundamentals.

Here he tested straight stack vs. a tapered one

tapered.jpg

As you can see the straight one is more progessive.

Therefor the tapered one got less HS damping!

So what would be really interessting is if you replace faceshims by certain HS shims.

eg. a stack like:

7x 24

22

18

14

11.25 (clamp)

You got pretty less HS shims, but plenty of faceshims. It goes more in the direction "straight stack"; progressive!

So now you change it like this

4x 24

22

20

18

16

14

12

11.25

3 faceshims removed, replaced by appropiate HS shims.

You go more in the direction tapered stack. In theorie you should get less HS, but remember: You cant alter just HS or LS, it always works in both directions (more or less).

I cant answer the question 100% because this was also a szenerio I wanted to test on my bike (according to some input I got), but I wasnt able to do it...

Its another story if you look at dualstage shimstacks. I recommend you that thread:

http://www.thumpertalk.com/forum/showthread.php?t=721853&highlight=crf%20450

pretty nice info there!

What would be the affective difference between these two bv fork stacks?

30 30

28 28

26 26

24 24

22 22

20 20

18 18

16

14

12

Stiffer/Softer?

What does a longer taper do for the feel?

IMO, there's some missing information here, and some assumptions being made in the answers given.

One piece of missing info is the thickness of the shims, but I think for the sake of the discussion it's probably safe to assume them to be of an equal size in that regard.

But I don't think that the 12 or 18 mm shim listed in the too stacks above are the actual clamping surface. The reference to the effect of the diameter of the last shim depends on that shim being clamped against an inflexible surface with a diameter at least as large.

Say that you have an 8mm valve stem that rises off of a 20mm flange so that the smallest shims you list sit directly against the flange. In that case, the first stack will be softer since the 14 can bend over the 12, the 16 over the bending 14, and so on. By comparison, in the shorter stack, the 18 can't bend, so the whole stack is restricted to lifting from 18mm out to 30, instead of the much larger area defined by 12mm inner diameter of lift. It also requires less force to lift the face shim 1mm in the stack with the 12 at the bottom.

However, the reality is probably represented more by something like what's been posted by Vietze, in which there's a thicker, small clamp shim like the 11.25 he shows. These are often 2mm thick or so. If such a shim (many would just call it a washer or spacer) exists under your two stacks, it changes everything. In that case, the 11.25 becomes the fulcrum over which both stacks bend, and the shorter stack is the softer, since the 30-18 will bend over the 11.25 rather than over the extra stiffness added by the 16-12.

you guys should keep going....

first time im hearing certain explanations that are starting to make sense to me about suspension tuning.

Wow. Now that it has explained I see where I have been wrong in my conclusions. I just tinker on my own bikes but I am intrigued with the mechanical concept behing damping now that I opened the forks up.

Given, in all scenarios, that the last him is a clamp. The smaller the clamp, the the less restrictive the oil flow.

If it is the base shims that help keep the forks higher in the stroke, but also are more restrictive to oil flow making the forks stiffer how would keeping a higher spring rate, but fewer base shims impact the damping through the stroke?

Thanks for everyone's expertise.

less shims but more spring will also hold it up, the system has to be viewed as a entire system with each part playing its own role and they all interact

less shims but more spring will also hold it up, the system has to be viewed as a entire system with each part playing its own role and they all interact

:thumbsup: yep. good point. the relationship between bv/mv is something to be addressed as well.

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