[arnea]

Yes, but the ratio is same for .01 and .02 mm shims. You need 8 .01 shims to get stiffness of single .02 shim.

 

[tigris99]

Dude for the love of God, I don't have my sheets around to look at SO I WAS USING RANDOM NUMBERS, get over it. Ratio is 3:1,8:1,or 100:1 I don't care, was a simple point I was trying to make to explain regarding just use one thicker shim instead stacking. Basically don't over think it cause it's a waste of time.

What part of I don't use my sheets (and I don't use more than a couple of the same shim diameters stacked) did you miss???

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[arnea]

Dude for the love of God, I don't have my sheets around to look at SO I WAS USING RANDOM NUMBERS, get over it. Ratio is 3:1,8:1,or 100:1 I don't care, was a simple point I was trying to make to explain regarding just use one thicker shim instead stacking. Basically don't over think it cause it's a waste of time.

Ok, I didn't realize that all the number weres random. I thought that only thicknesses were selected arbitrarily.

What part of I don't use my sheets (and I don't use more than a couple of the same shim diameters stacked) did you miss???

I just tried to correct what seemed to be an error.

 

[tigris99]

No I just tried to give an idea, my print outs probably got thrown out last summer and have a new phone now so didn't have the PDF either.

But for reference cause this thread is insanely long now, here's a good place to get a variety of shims. It's where I get mine vs buying the entire manitou kit.

http://www.racingsuspensionproducts.com/shim/shim.html

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[GrayJay]

Tigris, Arnea- Thanks for the info and feedback.
I do a lot of riding on climbs so I think I want to keep a bit of platform in order to be able to eliminate pedal-bobbing while climbing. The stock XC tune CV-11411-03 was definitely stiffer than I liked but I am pretty happy with XC tune CV-11411-04 achieved by adding a single 10mm OD x 0.25 thick preload reducer shim below the two stock 19mm platform shims. The preload reduction cuts the platform and force curve roughly in half from the original CV-11411-03 tune. I also like being able to keep the LSC adjuster closed or just cracked open a click or two in order to reduce brake dive compared to a tune where I would need to open the LSC further to keep it somewhat plush.

I did a bunch more reading and came to the realization that it would be fairly difficult project to write a simple spreadsheet that would somewhat accurately predict all the possible shim stacks. From the documentation, it does appear that the restackor program can be configured to handle the complex fluid dynamics and shim pre-load that are produced by the 0.6mm lip on top of the ABS+ port. Purchasing the restackor program to do the modeling would be a bargain compared to the time involved if someone actually needed that level of info.

As far as I got was to calculate the spring constants for the standard individual ABS+ shims. Even just doing this requires some fairly complex calculations. Individual shim stiffness is influenced variously by both the outside diameter and the inside (hole) diameter, by the height of the shim and by the ratio of the height to the OD.
As you pointed out, increasing the shim thickness has a cubed effect on the individual shim thickness (thicker shims are stiff). What is not quite as intuitive is that for a fixed shim ID (8mm) and thickness, a reduction of the OD produces a stiffer individual shim. Rather than tackle the shim stiffness calculations myself, I found an engineering spreadsheet designed for calculating "Bellville spring" (dished disk springs). Bellville spring stiffness behave much differently if they are manufactured with excessive concave/convex dishing, but you can use the same equation to calculate stiffness of a flat shim by just setting the overall height of the dished spring a tiny bit more than the shim material thickness. The spreadsheet generates an error if you put the Bellville spring height exactly equal to the shim material, but it works fine if you enter a overall height of 0.21mm for a 0.20mm thickness shim. Spreadsheet I used was downloaded from; Excel Belleville Spring Calculator

I ran all the standard ABS+ shims and came up with the following spring rate constants (K) for shims all of 8mm ID;

OD (mm)_H(mm) K(N/mm)
19mm____0.2____ 27.6
19mm____0.15____11.6
19mm____0.1_____3.4
17.5mm__0.2_____33.5
17.5mm__0.15____14.2
17.5mm__0.1______4.2
17mm____0.2_____36.0
17mm____0.15____15.2
17mm____0.1______4.5
15mm____0.2_____49.8
15mm____0.15____21.0
15mm____0.1______6.2
13mm____0.2_____75.6
13mm____0.15____31.9
13mm____0.1 _____9.4

Comparison graph of the results looks like;

Admittedly none of this does much to directly predict the combine complex behavior of shims stacked together which are of different OD. A common MX shim stack configuration is to have a large OD shim on the bottom and stack against the valve port and gradually tapering springs stacked on top. The resulting tapered shim stack should have a combine stiffness that is a bit less than the combine individual shim stiffness because the large shim hangs out from beneath the smaller, stiffer shim above and so is only partially stiffened by those above. Still, just knowing the relative stiffness of individual shims should be helpful for selecting shims for an experimental stack..

Unfortunately, I dont see an obvious direct relationship between the calculated shim spring rates and the observed blow-off force needed to overcome the platform level of the XC tune stacks.

 

[tigris99]

The platform shims have preload. That's what creates the platform. If you noticed when you were making changes, there is a raised lip that the platform shims rest on. When you tighten the assembly the shims are compressed into a dish shape. This removes the normal spring rate. Instead it requires a certain level of pressure before they "pop" open.

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[GrayJay]

As I understand spring physics, you should be able to multiply the spring rate constant (K) by the amount of pre-load deflection to determine the force needed to lift the shim off of the lip.
For a 19mmx0.2t shim pre-loaded 0.6 mm, the calculated force to lift the shim is thus 27.6 N/mm x 0.6mm = 16.6 N.

If you look at the graphs for pre-loaded tunes CV-11411-03 (using two 19mm shims) and CV-11411-07 (using three19mm shims) and divide the blow-off platform force by the # of shims, this tells you that each of the pre-loaded 19mm shims contributes an average of 254 N of force to the platform so a bit over 1 order of magnitude difference from my calculated springs. You would also need to include in the calculation that the 11mmx 0.5T clamp shim above the pre-load shim would stiffen the 19mm shims to function more like a 19mm OD shim with a 11mm ID (instead of actual 8mm ID), the 11mm clamp should make the platform shims around 20% stiffer.

All I can think is that perhaps somehow I miscalculated the spring-rate constants at 1/10 the actual rate, in which case the calculated force 165N x 120% = 200N would be a bit closer to the observed chart blow-off force of 254N per shim.

 

[tigris99]

Dude, your making me think to much . I understand all that but my "mental capacity" prefers led lighting systems[emoji14]
My guess would be like I said, your over thinking it so probably made a very simple mathematical mistake is all. Recheck your calculations but keep it simple, one piece at a time. Especially if I understand you correctly and your off by a factor of 10. Simply forgot a 0 or accidently put a decimal in the wrong spot. IT HAPPENS, don't dwell on it.

And there is alot of other factors in how a fork will perform. So if your doing all this just to "analyze and understand" then awesome. You have more patience than me (but I do the same with LED bike lights and flashlights). If your doing this to determine best shim set up, your beating your head on a wall. Ambient temperature, air chamber pressure, riding position, bike geometry, and the list goes on will screw up what you think your accomplishing. Too many variables.

I'm hoping for the former (cuz you can) instead of the latter. Be nice to have another "analyst" dealing with manitou forks. Couple good guys here already, but except Mullen, their not around much. And I personally prefer the "try-ride-try something else-ride again" technique. DONT THINK, DRINK (well ride then drink )

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[GrayJay]

Analyzing the shim springs was definitively just a fun intellectual amusement, not an outright replacement for try-it-and-ride-it tuning. Understanding the relative individual shim spring rates however did help me with interpreting the manitou example shock dyno tuning charts and I think I would have an easier time with developing custom shim stacks.

 

[ashwinearl]

. I ride cross country and use light linear stack with low speed needle almost closed - it has very good small bump sensitivity and good midstroke. I like to spin (no out of saddle sprints) and this stack fits me very well.

Could you describe the linear stack you are running. Your riding style sounds a lot like mine. Can you describe it starting from the clamp shim (what size ) and then going to the piston?

Thanks. I've been on Clamp | 15x0.15 | 17x0.2 |Piston and it has been ok.

 

[arnea]

I had the standard Trail stack (11x0.5 clamp, 2x19x0.2 preloaded shims and 17.5x0.2 speed shim). I removed both preloaded shims and added 17x0.1 shim on top of existing speed shim.

 

[tigris99]

What are you talking about, none of that has anything to do with what we are discussing??? Everyone modifying shim stacks has the manual and knows how to do the work so wondering why you posted that?

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[ashwinearl]

Did u change the oil in the damper? Did you check the oil level as shown in manitou manual? Did u compress forks several times with dampers set full open and then let sit so air trapped in the fluid can escape to the top of the damper?

Actually, I'm glad minkitkat posted this. It's a good reminder to me as sometimes I forget to do this or am not patient enough to follow the procedure correctly. I'm sure my oil level has been off because of this.

 

[tigris99]

Wanted to report back. Changing to prep m in the air chamber and going linear stack is amazing. I ran LSC 3 clicks open and no dive issues at all, Bob was unnoticed and small bump compliance was freaking amazing. 120mm seems to have brought the bike to life too. Smoother control leaning in the corners and much more stable coming down without killing response to steering inputs.

Like riding a much more fun and new bike lol. And the 30% sag is enough that I can still keep the weight forward on the climbs without issue

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[NH Mtbiker]

So I am a newbie with Manitou forks. I previously owned an X-fusion Velvet in 2011 that was fairly easy to service, as I had installed Enduro fork seals no problem. I am now a proud owner of a new 120mm Mavel Pro 29er fork and not a clue, until now somewhat, how to go about opening it up and changing oil, seals or removing platform shims. I just went to the Manitou support online and opened up this service video:

My first question is - is this video relavent to my Marvel Pro in any way? I quickly noticed the Mattoc requires 3 specialty tools: flat ground 24mm socket, 8mm thin wall socket and a cassette tool. Any chance these are also needed on the Marvel?

I have also been told that I may want to loose the platform shims altogether in an effort to gain plushness and small bump compliance.... is this also true?

I think the right thing to do first is ride the snot out of this fork for 30-50 miles and then decide what needs to be done under the hood, yes? Great info here and enough to make my brain hurt, but thanks!

 

[fishwrinkle]

if it were me, like you said ride the piss outta it before opening it up. except mine took much more than 50 miles to break in.

 

[GrayJay]

I dont think that the mattock video is particularly applicable to your marvel, the mattock is a more complex fork. You can get the ABS+ dampener out of your marvel for tuning in just a couple of minutes work just using normal hand-tools, see post #1 of this thread and start reading through the manitou tuning training manual; http://goo.gl/JaqWO

 

[tigris99]

Do NOT take out all the platform shims UNLESS you buy "speed shims" to tune with in their place. Removing the platform shims in the marvel means removing ALL high speed damping shims.

Unless manitou changed it the stock abs shim stack is 2 platform shims and nothing more. Ya u need shims in there or you want have any damping.

Manitou has a service manual on their website. Marvel forks are INSANELY easy to work on with standard tools. But it's not something you should do without good reason. Many snap off the damper shaft not taking the forks apart properly

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[Dougal]

So I am a newbie with Manitou forks. I previously owned an X-fusion Velvet in 2011 that was fairly easy to service, as I had installed Enduro fork seals no problem. I am now a proud owner of a new 120mm Mavel Pro 29er fork and not a clue, until now somewhat, how to go about opening it up and changing oil, seals or removing platform shims. I just went to the Manitou support online and opened up this service video:

My first question is - is this video relavent to my Marvel Pro in any way? I quickly noticed the Mattoc requires 3 specialty tools: flat ground 24mm socket, 8mm thin wall socket and a cassette tool. Any chance these are also needed on the Marvel?

I have also been told that I may want to loose the platform shims altogether in an effort to gain plushness and small bump compliance.... is this also true?

I think the right thing to do first is ride the snot out of this fork for 30-50 miles and then decide what needs to be done under the hood, yes? Great info here and enough to make my brain hurt, but thanks!

The marvel is a lot easier to service than the Mattoc. No special tools.

Just remember the damper side (8mm hex) screws INTO the fork to remove it.

 

[arnea]

Manitou has service manual up in their site: http://www.manitoumtb.com/assets/Service Manuals/2012 Service Manual.pdf It's old, but contains all the information you need.

You can get shims from here: Revalving Shims You need 8mm ID shims. Get couple of 17mm OD shims with 0.1, 0.15 and 0.2mm thickness. Also you might want some thicker (e.g. 0.25mm) shims with 10mm OD if you decide you need some light platform. You can use those to reduce the preload of the platform shims.