2010 Marzocchi 888 Evo tuning thread

[Hacktastic]

Been getting lots of trail time on mine. You can run the compression pretty far in without it getting harsh on the trail. Completely different damper than they've had in the past.

[acair422]

Is this with the factory shimstack or have you made some personal changes...

[Hacktastic]

Haven't even touched anything on the fork yet besides adjusters. Not sure what I'd want out of a revalve yet, if anything.

[X777]

It has been said that the gold knob on the bottom controls is a low speed bleed to bypass the shimstack in the base valve. Now, I have been wondering... what does a base shimstack do? Does it take care of the high speed region of compression or fiddling with it adjusts the range of the low speed region?

[dilzy]

Base valve shim stack covers entire speed range when needle is closed. The fact that it is the base valve and not the mid valve simply means that each shim has less effect on the amount of compression damping, as the ratio (similar to a brake master/slave ratio) of rod movement to oil displaced is quite high.

Due to this very high ratio, you may notice a tiny amount of slop in the stroke, where compression valving on the mid-valve would add an immediate firmness that you can't get on the base without it being harsh. I tried it on my 36, but couldn't stop the cavitation which will occur without pressurization.

It's the same system every fork and shock manufacturer (except DB and Vivid) uses. The shape of the base shim stack can be made to have most effect over any particular speed region. EG: Flat=Lots of low speed with linear progression; Christmas tree=harder progression, ect.

[dilzy]

What's everyones verdict on the chassis? WC or Standard?

[X777]

Well, I have been lucky enough to get the 888rc3evo ti. Unfortunately I wasn't able to weigh it, as I didn't have scales with an appropriate range. But I strongly believe that it is close to 3kg as Zoke says.

Before mounting the fork on to my bike I took it apart to check the amount of oil and grease and to satisfy my general curiosity . Oil volumes were just as Zoke recommends, there was plenty of grease on the seals. There is a new foam ring under the dust viper similar to what fox and Rs are using in their forks. As far as I remember most of the parts in the fork are anodized and generally well made - high quality, no plastic crap anywhere...

Can't really comment on performance yet, but initial impressions are great. Fork is very smooth out of the box, I have been on it only 4 days in quite cold weather conditions (where my friends boxxer team was well frozen and he was getting like 10cm of travel ) fork was still behaving pretty decent, there is enough support from new damping so the fork doesn't blow through it's travel as much my 888rc2x did and yet I don't feel that it lost any of it's suppleness and it is noticeably stiffer. So in short it's stiff, well built, with good weight and a high end fork. We shall see how it holds up but I do have a lot of faith in it. Can't wait for the summer.

Back to your post. So you are saying that if I want more LSC I need to cut down the Christmas tree and make it all flat? What an industrialist way of thinking.
Replacing smaller shims visible on the picture with bigger ones or same size as is the biggest one = more LSC ?

Excuse my english it's not my native language...

[davep]

Changing the shim stack changes the 'knee' on the damping graph, or the threshold between the LSC and HSC. The shape of the curve below the knee is 100% LSC and is not changed by modifications to the shim stack. Adjusting the needle valve is the only way to change the shape of the LSC curve:



The following graph shows the change in overall damper curve via changes to the first shims in the shim stack. You can see, that the curve below the inflection point (knee) is always the same shape...what does change however is the point where the shims open, and the regressive HSC takes over

To stay in the LSC region 'longer' you need to make the shim stack such that it takes more force to open. Stiffer or more large shims next to the piston face are one way to do this.


The further away from the piston face....you are effecting the regression of the HSC curve. If the tapper in shims is agressive (fat short pyramid) the curve will be more regressive. If the shim stack tapers less, the HSC curve will be less regressive in nature.


Images as well as some very good reading from here: http://www.peterverdonedesigns.com/damping.htm

[Hacktastic]

Think of it as a "timing switch" for the HS stacks almost. That's crude, but kinda the way it works, especially with an adjuster that has a range from freeflow to fully closed off.

[RedOne]

This link might be interesting for all you suspension tuning nerds
http://shimrestackor.com/Code/Sample...ack-config.htm

[dilzy]

Nice post Dave. Thicker face shims often are the easiest way of obtaining more l-msc damping, but you don't want too much, because you'll start to ruin your traction.

[X777]

Thanks for great the post dave and to all other guys too.
I would like to find out more about this particullar case ( rc3 evo).
My theory is : Unless the LSC needle is fully closed, the shim stack controls HS region of compressin and as dilzy said when it is fully closed it covers the entire compression range... What are your thoughts on this guys??

[dilzy]

The shim stack in practice with the needle open around mid way (obviously this depends on the size of the bleed hole) will cover a range from upper LS all the way up. On forks where there is a spring backing the stack, the spring controls high, stack mids and needle low. Personally I like to have the stack such that I have the needle closed off to let the shims do all the work.

[X777]

what fork are you on ?

[dilzy]

888rc2x wc right now. Woeful when you want some lsc damping, but nice and supple. All my tuning experience comes from my 2 Fox forks (40 and 36) and my Ohlins forks on my moto.