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Shim ReStackor calculation

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Can someone with the Restackor program do a calculation for me. The first part of a Suzuki RMZ250 rebound stack has 7-20.1 shims followed by a 10.1 crossover. I would like to know what the equivalent number of 20.1 shims would be if I replaced the 10.1 with a more traditional 13.1 or even a 12.1 crossover. Thanks in advance.

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oabike,

Here is what I found for a stock '11 rmz250 fork rebound shim stack on the Valving Logic web site.

1-rmz250-stk.png

If you replace the 10.1 crossover with a 12.1 crossover it looks like using 3x20.1 face shims puts the stack stiffness pretty close to the stock shim stack.

2-rmz250-12co.png

For the 13.1 crossover things don't work out as nicely. 2x20.1 face shims are too soft and 3x20.1 face shims are too stiff.

3-rmz250-13co.png

I hacked around a bit on the taper with the 13.1 face shim.

4-rmz250-13mod-stk.png

.... and got the stack a bit closer.

5-rmz250-13mod-y.png

Not sure where you are going with the stacks. If you start hacking around on the taper you can get all kinds of different curves.

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An interesting thing is comparison of the '09 vs '11 fork rebound stacks for the rmz250.

6-rmz250-stk-cmp.png

The '09 uses a conventional crossover configuration. The crossover shim diameter is less that the stack clamp and the face shims are much softer than the tapered section.

The '11 also uses a crossover shim diameter that is less than the clamp but the face shims are stiffer than the tapered section.

For the '09 stack the soft face shims and stiff tapered section cause an "event" when the crossover closes. It is pretty easy to pick out where the crossover closes on the FEA stack stiffness curve.

7-rmz250-09y.png

For the '11 stack the effect is a little more subtle. Looking at the stack deflection the crossover closes with a force around 4 lbf on the stack.

8-rmz250-11stk.png

But that does not produce much of an effect in the stack stiffness curve.

9-rmz250-9v11y.png

Those differences create a much different damping force curve for the '09 stack compared to the '11 stack.

10-rmz250-9v11c.png

The '09 stack produces very little low speed damping since the crossover blows open right away.

The '11 stack has a lot more low speed damping and ends up around the same damping force around 100 in/sec on the fork.

Personally I like the '11 configuration with the higher low speed damping on the rebound side. Others likely have a different opinion.

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my fast rider like much no crossover and more low speed damping on rebound

but i found rider want a faster rebound in the first fork travel.but i think the bike is not precise in corner

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I agree. Thanks. Is the restackor program relatively simple to navigate?

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I agree. Thanks. Is the restackor program relatively simple to navigate?

That is a hard question. Here is what is involved:

First you have to fill out a table with the shim stack configuration.

11-stack-io.png

Nothing hard there. But tedious if you are using 50 shims in a fork base valve. :lol:

Then you need some basic measurements on the valve port configuration.

12-valve-geom.png

The dogger describes those measurements as difficult and error prone. I suppose using a tape measure it would be. To get the geometry measurements you need to go over to Harbor Freight and blow $20 on a digital caliper.

14-harbor-freight-caliper.png

With that you can measure the valve ports to +/- 0.03mm and you are going to need the caliper anyway to measure the shim dimensions.

Mog started a thread here with dimensions for a couple of valve geometries. With those measurements you can fill out the valve geometry inputs.

13-geom-table.png

....... and thats the whole deal.

15-spreadsheet.png

Navigation wise it depends on whether your are familiar with running and plotting data in spreadsheets. You might find that tuff. I am running the OpenOffice freeware stuff -or- you can run excel.

The best way to figure out whats involved is to download the demo spreadsheet and start hacking around on it.

I'm sure others would like to hear your feedback if you get a chance to test it out.

Let us know..............

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do your port calculations account for the webbing between the ports? case in point; the open flow on the early showa "works" style pistons, where the ports are not isolated from eachother as they are in the subsequent piston designs.

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Almost everyone who rides the new rmz LOVES the way it handles. I think while the chassis is a huge part of this - it should be clear that the suspension settings/rebound setting also is a big player in making it feel precise/connected to rider.

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I just purchased the Restackor pro and I try to figure out how to use it.

The pic below is what I obtain for a KTM 350 SX-F 2011 MVr.

I'm not able to have the damper coefficient plot. It works when I play with the demo stack.

Clicked or someone else, could you run your Restackor with these spec and let me see your result please ? I have tried for hours and now I need to know if the issue is my software (I run it with window 7 ???) or if it's still between the computer and the chair :bonk:

Thanks you for your help.

DSC00038.jpg

Here is the MVc dimensions. The OEM Float is 0.6mm (1.9mm-stack high mm)

D.rod D.valve w.seat Vspec

0 23 1 MVc

r.port d.port w.port N.port

5.3 4.2 8.5 3

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Without paying an attention to your specific dimensions I would just change the scale of Y axis-it is an easy task:)

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Thanks suhoi27, it's working.

I did it before but from 0.005 I tried at 1 and stopped. It's working with 8.

I'm glad the problem was me !!!

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texasthierry: Nice screen shot! :bonk:

The other way to go is [alt] [Print Screen] open a photo editor and paste the screen shot from the clipboard. Then you can save it as a jpg or whatever.

For some photo editors you can paste in plots from excel the same way to make them jpg's for posting on the web.

Or just use a camera...........

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