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Suspension Theory
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Also I learned this the hard way, take some time to understand the differences of shim thickness, a .12 is about 3 times stiffer than a .10!!! My suspension was soooo stiff on small chatter but great on big hits and I got lost in adjusting my mid valve in all different configurations. Turned out one day I was on Thumper Talk and a random post said “remember the blue KYB shims are .12 not .10 so that makes a big difference” I was using a analog micrometer and couldn’t really tell the difference and ordered a digital... I’ll be damned half the shims in my Mid Valve and compression stack were .12 shims 🤦♂️
I went back and re installed the original stacks I had in all .10 and it was rideable again and worked well! It’s little stuff like that, that will drive you insane but when you learn from your mistakes it’s rewarding!!!
Introduction/Theory to fluid dynamics (rent a book from your local library and learn the basics)
The Shop
This thread on TT made me feel pretty stupid for awhile... when it all starts to make sense you read it again and have this look on your face and realize you don’t get it!
The mid valves in forks can be very restrictive. A lot of the harshness on chop - assuming you have a reasonable spring rate- is the mid valve being toooo stiff. So if you're getting too much feed back on chop... sharp edged stuff with the forks; Try opening up the float and lighten the mid valve. A mid valve change has more effect then a base valve change (pull one shim from the mid value and you'll feel it.. the base valve you'll barely notice it). Make big base valve shim changes as a result. My mind set now is to go with higher oil levels in the forks and softer on the valving to get the small bump compliance I want... I tune till the forks is too soft then add stuff back in... Vs staying too stiff. I want that small bump compliance and will give up some bottoming resistance. Especially for off road.
On shocks pay attention to the pivot shim size. That is the last shim in the stock.. the smallest diameter one. Changing the piviot shim can effect the entire stack.
I setup shock initial compression to be softer then stock most often. Often I will put in a bleed shim between the shock piston and the first shim that will be big enough in diameter to cover the piston (compression side). Why? That little bit of bleed helps the bike track under power. The shock moves a bit freerer and hooks up better. This is similar to drilling out the bleed hole in the shock piston (if there is a hole). It can be undone too. Some of the best shocks I've ever valved had this done to them and they hocked up... clawed at the ground. I've put a few bleed shims in too... Had to do this to a KTM 350 due to the stock linkage setup. To get the bike to move on small chop. Yes you can go too far and it will blow through. But you need to experiment and find these points. You'll learn alot about what you like and don't like.
On shock rebound: I like my high speed rebound to be stiffer then stock. When the shock is deep in the travel I want it coming back SLOW from a hard hit. Now, I m not hitting super cross woops etc... this is mainly for off road which is where I spend most of my time. I go for cross overs higher up in the rebound stack to let the shock move in the first part of the stroke for compliance - then stiff up the high speed part of the travel to control it.
Note: I don't go near a supercross track... so none of what's above would apply there. Supercross is a different animal and I have nothing to add to setup for that.
There’s an Ohlins shop manual floating around on the web, has some good info about shim selection and the math to convert to different size shims.
Restackor is a computer program that can help graph and plot shim changes, There is a ton of info on the site as well.
TT suspension form has been the biggest help to me, I don’t really know anything.
I have looked at the restacker program though I never bought it. It looks like it could be a benefit. I guess one question is.....are you just doong this ofr yourself and a possible living?
Race Tech used to include valving charts in their God Valve kits but they no longer do so. Many will debate the good or bad of Gold Valves but they are still an excellent place to start ofr the DIY guy.
Lots of good advice in here!
One thing to note, as Honda65 said "And you have to be willing to go back and tear it down again (and again and again)."
Honestly, once you do it a few times, you can do it FAST. But it IS messy!!! You will be much more inclined to dive into it if you have a proper, dedicated work space to do suspension and contain the oil that will be flying around.
Not doing this for a living, just for me personally. I’m in the military and move around a lot, so sometimes my suspension needs change with the terrain and in some cases exceeds what I can adjust for with the clickers.
I’ve been riding for a long time and am in tune with how to adjust my suspension and set up my chassis, but translating that to a valving change is a blind spot for me.
He kept reminding me that it's a black-art and One needs to have an open mind. Do not be afraid to experiment.....that applies to everything on the bike.
Trend monitoring - it crucial to document everything you do in a note book and use the data as a references going forward.
There are suspension tuning books and DVDs out there.
What this gentleman said above is very true. I 100% agree. I did some work on a friends bike - he's pretty darn fast - and the only feed back he could give me was "it feels different". I was like... "huh.... ahh... need more info than that".
You also have to know what you like. Or at least are willing to experiment to find out what you like. I like stuff that absorbs chop. I don't like getting pounded by sharp edged chop. So I set the bike up to adsorb that stuff first and foremost.
Thanks again. You guys are awesome.
Like Boomslang said, keep a notebook and make lots of notes and keep track of every little change. It will start to make sense. Also, keep in mind there are many ways to create a valve stack that will get similar results.
Boomslang- do you have that photo of your suspension bench set-up?
https://www.ohlins.com/app/uploads/world/documents/2005/05/OM_07430-01…
A common blady problem and one needs to dig deep to find the patience.......
Ill dig up some old photos of our sus department from back in the day.
Pit Row
https://www.facebook.com/Restackorandsuspensiondatabase
We've been working with this program since 2015 and it's really come a long way. It's not the end all of testing but it really shows us how far off the OEM settings are. We find a lot of problems and solutions this way. The amount of work and time is insane but worth it. If you really want to learn how stuff works and why the type of changes are necessary there is no other way.
Just remember. Garbage in Garbage out. It's not a black art. It's just pressure and math. There's always multiple ways to end up at the same point. My purpose is to find it with the least cost and make it easily repeatable but customize it for each individual.
.10 to .15 you multiply by a factor of 3.4
https://www.youtube.com/watch?v=dRekn0iRiRs
https://www.youtube.com/watch?v=BiclqTlRWFg
https://www.youtube.com/watch?v=nfjehrb0QFE&t=250s
https://www.youtube.com/watch?v=AzI2IEns3WY&t=446s
https://www.youtube.com/watch?v=mgR4PJwEHMg
https://www.youtube.com/watch?v=KPWzyBh6iN4
You are correct in my rush i mistyped .12 for being about three times stiffer as it is 1.7 and yes KYB shims are “exactly .114” but still NOT .10!
I have in my notes
0.10=1
0.12=1.7
0.15=3.4
My point was to double check your work and ensure you are as accurate as possible. I identified a simple mistake when building my stack that made a big difference in my set up and was hoping to be helpful to someone that might be in the same situation I was in. I made this revelation after working on my own suspension for over 25 years because my analog micrometer didn’t show the difference like the digital one I use now.
To expand this even further I found this to very interesting as well.
The stiffness of a shim is not linear in relation to its thickness. If two 0.15 mm shims are stacked together the stiffness will not equal one 0.30 mm shim. In fact it takes a little more than eight 0.15 mm
shims to equal one 0.30 mm shim. To
calculate how many thin shims it takes
to equal one thicker shim the formula is
approximately the same as for comparing the stiffness of dissimilar constant section beams. The procedure is to divide the thicker shim by the thinner shim to get the ratio between the thicknesses of the shims. Then if you cube the thickness ratio you will have an idea of how many thin shims it takes to equal one thicker shim.
for Example
0.30 ÷ 0.15 = 2.00
2.00 cubed (2.00 x 2.00 x 2.00) = 8.00
Hence:
0.15 x 8.0 shims = one 0.30 shim
yes i’m not this smart and stole it from Thumper Talk… but it has also helped me tremendously. I love learning about this stuff and continue to try my own stacks when I can on my own stuff but not at the point i would want to work on someone else’s.
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