Theory of damping and rebound, and building shimstacks!

kb228 wrote:

Racetech suspension bible

UGOTBIT wrote:

The RT book is good, BUT there is not a lot of actual valving info inside. I would also like to find other books/info, I see...

The RT book is good, BUT there is not a lot of actual valving info inside.

I would also like to find other books/info, I see KYB has books/manuals listed in the Technical Touch catalog but do not have any info on them?

There’s also some Öhlins shock manuals floating around, they had some good info about shim selection/sizes.

Restackor is a computer based program, may be helpful for comparing but looking at the graphs doesn’t exactly translate to feel. Some really great tech info on the site also.

h_reed wrote:

https://www.ohlins.com/app/uploads/world/documents/2005/05/OM_07430-01…

Best info around.

Lasse wrote:

Hi! I'm interested in learning the theories of what goes in to revalving suspension. From damping defining damping curves to practical selection of shims. But I...

Hi!

I'm interested in learning the theories of what goes in to revalving suspension. From damping defining damping curves to practical selection of shims.

But I haven't been able to find any valid sources yet.

Can you guys recommend any sources? Books, publications or anything relevant is appreciated.

heatedcheese wrote:

All depends how far down the rabbit hole you want to go. If you are dead set on learning the theory, pick up an engineering book...

All depends how far down the rabbit hole you want to go. If you are dead set on learning the theory, pick up an engineering book or two on fluid dynamics and control theory. Those will teach you the actual math that goes into what your suspension does and not just what to tune but why. For 99% of us though that’s more time and effort than is needed to make a bike ride well so all of the above references are substantially more practical.

bvm111 wrote:

Lots of trial and error if you are doing it yourself and just remember that KYB shims are .11 not .10 like Showa and what comes...

Lots of trial and error if you are doing it yourself and just remember that KYB shims are .11 not .10 like Showa and what comes in RT goldvalve kits and that makes a big difference. They are hard to differentiate with a analog dial micrometer so use a digital. It doesn’t sound like much but that works out to be appx 48% stiffer than .10 and .15 shims are like 3 times as stiff sooooo don’t mix them up... ask me how I know and why my wrists hurt 🤦‍♂️

bvm111 wrote:

Lots of trial and error if you are doing it yourself and just remember that KYB shims are .11 not .10 like Showa and what comes...

Lots of trial and error if you are doing it yourself and just remember that KYB shims are .11 not .10 like Showa and what comes in RT goldvalve kits and that makes a big difference. They are hard to differentiate with a analog dial micrometer so use a digital. It doesn’t sound like much but that works out to be appx 48% stiffer than .10 and .15 shims are like 3 times as stiff sooooo don’t mix them up... ask me how I know and why my wrists hurt 🤦‍♂️

coastlinecascot wrote:

That is good to know. I thought my calipers were off when I first started measuring kyb stuff. I ended up only using racetech shims and...

That is good to know. I thought my calipers were off when I first started measuring kyb stuff. I ended up only using racetech shims and sdi shims. I might still have some kyb stockers in there.

bvm111 wrote:

Lots of trial and error if you are doing it yourself and just remember that KYB shims are .11 not .10 like Showa and what comes...

Lots of trial and error if you are doing it yourself and just remember that KYB shims are .11 not .10 like Showa and what comes in RT goldvalve kits and that makes a big difference. They are hard to differentiate with a analog dial micrometer so use a digital. It doesn’t sound like much but that works out to be appx 48% stiffer than .10 and .15 shims are like 3 times as stiff sooooo don’t mix them up... ask me how I know and why my wrists hurt 🤦‍♂️

coastlinecascot wrote:

That is good to know. I thought my calipers were off when I first started measuring kyb stuff. I ended up only using racetech shims and...

That is good to know. I thought my calipers were off when I first started measuring kyb stuff. I ended up only using racetech shims and sdi shims. I might still have some kyb stockers in there.

bvm111 wrote:

The KYB are usually a blue color so you can spot them I just couldn’t tell the difference with my old dial indicator. I read a...

The KYB are usually a blue color so you can spot them I just couldn’t tell the difference with my old dial indicator. I read a thread on thumper talk and a guy mentioned it so I ordered a digital one and I’ll be dammed they all measured either .11 or .12 depending on how much pressure I applied. I also thought how big a difference could it be but the guy also had the calculations and I was stunned! I just finished about an hour ago getting them all out of there and replaced with all new .10 shims I ordered and will reassemble tonight after the loctite has had time to cure.

I’ve been doing my own work for 20 years and have been doing trial and error from the RT stacks from my gold valve kits so I was using extra OE shims to come up with different stacks and just trial and error and I could not get the harshness out of the braking and acceleration chop, it was fine on larger hits but solid like concrete on small stuff... it will be interesting to see if this makes that much difference but that’s the fun of it too the trial and error and testing!

coastlinecascot wrote:

That is good to know. I thought my calipers were off when I first started measuring kyb stuff. I ended up only using racetech shims and...

That is good to know. I thought my calipers were off when I first started measuring kyb stuff. I ended up only using racetech shims and sdi shims. I might still have some kyb stockers in there.

bvm111 wrote:

The KYB are usually a blue color so you can spot them I just couldn’t tell the difference with my old dial indicator. I read a...

The KYB are usually a blue color so you can spot them I just couldn’t tell the difference with my old dial indicator. I read a thread on thumper talk and a guy mentioned it so I ordered a digital one and I’ll be dammed they all measured either .11 or .12 depending on how much pressure I applied. I also thought how big a difference could it be but the guy also had the calculations and I was stunned! I just finished about an hour ago getting them all out of there and replaced with all new .10 shims I ordered and will reassemble tonight after the loctite has had time to cure.

I’ve been doing my own work for 20 years and have been doing trial and error from the RT stacks from my gold valve kits so I was using extra OE shims to come up with different stacks and just trial and error and I could not get the harshness out of the braking and acceleration chop, it was fine on larger hits but solid like concrete on small stuff... it will be interesting to see if this makes that much difference but that’s the fun of it too the trial and error and testing!

PTshox wrote:

For this situation - the harshness in braking and acceleration chop - three things come to mind. 1. Spring rate, 2 preload on that spring, 3...

For this situation - the harshness in braking and acceleration chop - three things come to mind. 1. Spring rate, 2 preload on that spring, 3 bleed shims.

First check to see how much preload you have on that fork spring. To get the harshness out of braking bumps go to little to zero preload on the forks.

You may also want to look at putting a bleed shim as the first shim on the face of the base valve compression piston (what fork do you have). That shim will be a very small diameter shim and it won't cover the piston ports. Say a normal shim is 24 mm dia the bleed shim will be 14 mm... maybe even two of them. Right against the piston. The first shim or shims. This will allow oil to pass through on the smaller chop. I've used this on both forks and shocks to get the bike to track and take the harshness out of the small chop.

Also, fork midvalve valving can be very restrictive on small bumps. So you may want to lighten that up...

Is this for MX or trail riding btw? And what fork is on your bike?

coastlinecascot wrote:

That is good to know. I thought my calipers were off when I first started measuring kyb stuff. I ended up only using racetech shims and...

That is good to know. I thought my calipers were off when I first started measuring kyb stuff. I ended up only using racetech shims and sdi shims. I might still have some kyb stockers in there.

bvm111 wrote:

The KYB are usually a blue color so you can spot them I just couldn’t tell the difference with my old dial indicator. I read a...

The KYB are usually a blue color so you can spot them I just couldn’t tell the difference with my old dial indicator. I read a thread on thumper talk and a guy mentioned it so I ordered a digital one and I’ll be dammed they all measured either .11 or .12 depending on how much pressure I applied. I also thought how big a difference could it be but the guy also had the calculations and I was stunned! I just finished about an hour ago getting them all out of there and replaced with all new .10 shims I ordered and will reassemble tonight after the loctite has had time to cure.

I’ve been doing my own work for 20 years and have been doing trial and error from the RT stacks from my gold valve kits so I was using extra OE shims to come up with different stacks and just trial and error and I could not get the harshness out of the braking and acceleration chop, it was fine on larger hits but solid like concrete on small stuff... it will be interesting to see if this makes that much difference but that’s the fun of it too the trial and error and testing!

PTshox wrote:

For this situation - the harshness in braking and acceleration chop - three things come to mind. 1. Spring rate, 2 preload on that spring, 3...

For this situation - the harshness in braking and acceleration chop - three things come to mind. 1. Spring rate, 2 preload on that spring, 3 bleed shims.

First check to see how much preload you have on that fork spring. To get the harshness out of braking bumps go to little to zero preload on the forks.

You may also want to look at putting a bleed shim as the first shim on the face of the base valve compression piston (what fork do you have). That shim will be a very small diameter shim and it won't cover the piston ports. Say a normal shim is 24 mm dia the bleed shim will be 14 mm... maybe even two of them. Right against the piston. The first shim or shims. This will allow oil to pass through on the smaller chop. I've used this on both forks and shocks to get the bike to track and take the harshness out of the small chop.

Also, fork midvalve valving can be very restrictive on small bumps. So you may want to lighten that up...

Is this for MX or trail riding btw? And what fork is on your bike?

PTshox wrote:

[u]See suggestions below...Underlined[/u] It’s for MX on my 2006 KX250 with 48mm AOS forks. I have RT gold valves and have worked with rob to develop...

See suggestions below...Underlined

It’s for MX on my 2006 KX250 with 48mm AOS forks. I have RT gold valves and have worked with rob to develop a “non standard” RT setting that keeps the MV due to my size and riding style as they usually recommend to remove. I just happened to have half of the shims at OEM .11 Mixed in rather than the .10 Since it wasn’t a standard RT stack I had to use the KYB ones to create the correct taper...so that was quite the revelation! I did measure my OEM springs today and they are 4mm shorter than the RT springs so I removed the spacers today when I had the forks disassembled .... so yes I had affective 8mm pre load 🤦‍♂️

Go to zero on the pre load. Take it all out...

What ICS spring rate do you have in there? Softer ICS springs help a bunch with the small chop. If you don't know... try putting a bleed shim on the compression piston in the base valve assembly. And reduce the number of shims in the base valve... lighten it up. Base valves are not as senative as mid valves. So you have to make big changes there to feel it.

Finally - open up the float all the way on the mid valve. You actually want that fork to move easily... Use the spring and the oil level to control bottoming. But it doesn't sound like bottoming is a issue. So go Soft on everything else till you get that small bump compliance you want. Make big changes to find out if you are going in the right direction. You can back up from there to get towards a sweet spot. In other words, don't make 1 or 2 shim changes when you're in searching mode. Make the changes drastic so you can feel them. The guy that ran FOX shocks power sports div for 20+ years taught me this... Big changes till you get in the ball park. Small changes when you get closer to where you want to go. Right now sounds like the sm bump compliance is off a lot... so big changes!

I am 225 vet int/exp depending on track and running .50 springs and running .30 float on the MV instead of the bleed shim.

Finally get to ride this weekend after almost 2 months off and excited to give it a try!