Custom Valving Coilovers: How to gauge shim stack and shock force graphs

[strat61caster]

Definitely use the adjuster if you can get the shock dyno to prove they're consistent, the stuff from the East has come a long way, seems like more and more people with access to the tools to verify trust the adjuster to be consistent not like it was ten to fifteen years ago.

What looks good in Excel rarely translates perfectly to the real world.

[FeRS]

Originally Posted by strat61caster

Definitely use the adjuster if you can get the shock dyno to prove they're consistent, the stuff from the East has come a long way, seems like more and more people with access to the tools to verify trust the adjuster to be consistent not like it was ten to fifteen years ago.

What looks good in Excel rarely translates perfectly to the real world.

Definitely going to get it dyno'd on multiple adjustment levels to see how it works, might get rid of the bleed shims then. Maybe I can have it set up for 5k front 6k rear springs on full stiff, and then 4k front 5k rear on a softer setting...

[Racecomp Engineering]

Originally Posted by FeRS

I'm aware, I have Bilstein 46mm COB pistons without the preload spring thing, so they should act as double digressive pistons. And by shim preload, do you mean the part on the piston or the preload shims? Or something else entirely?


Thanks by the way

The COB spring thing doesn't directly control shim preload but both have a large effect on low speed (bleed). Not everyone uses it, but Bilstein likes it and it has it's advantages.

EDIT: I think we're mostly talking about the same thing. The COB spring is a little confusing.

The preload shim(s) control how much the stack is preloaded. A thinner preload shim means more preload (the Bilstein digressive pistons are "dished"). Shim preload can control where the knee occurs and with the rest of the stack, how much it "blows off". Preload and the bleed shims have a large effect on low speed valving.

- Andrew

[FeRS]

Originally Posted by Racecomp Engineering

The COB spring thing doesn't directly control shim preload but both have a large effect on low speed (bleed). Not everyone uses it, but Bilstein likes it and it has it's advantages.

EDIT: I think we're mostly talking about the same thing. The COB spring is a little confusing.

The preload shim(s) control how much the stack is preloaded. A thinner preload shim means more preload (the Bilstein digressive pistons are "dished"). Shim preload can control where the knee occurs and with the rest of the stack, how much it "blows off". Preload and the bleed shims have a large effect on low speed valving.

- Andrew

Ah, got it. I'm planning to digress the damping around 3in/s so I might need to play with the preload and cover shims. By "blows off", do you mean the digressioin of the high speed damping force? I was under the impression the support shims on the tops of the stacks mostly controlled that.

[Racecomp Engineering]

Originally Posted by FeRS

Ah, got it. I'm planning to digress the damping around 3in/s so I might need to play with the preload and cover shims. By "blows off", do you mean the digressioin of the high speed damping force? I was under the impression the support shims on the tops of the stacks mostly controlled that.

By blow off I mean the "sharpness" of the knee when it digresses. The support shims control the high speed damping force, but the preload shim and cover plate can control where (lower or higher piston speeds) and with how much force the knee occurs. So the full stack needs to be considered when looking at the knee.

- Andrew

[FeRS]

Originally Posted by Racecomp Engineering

By blow off I mean the "sharpness" of the knee when it digresses. The support shims control the high speed damping force, but the preload shim and cover plate can control where (lower or higher piston speeds) and with how much force the knee occurs. So the full stack needs to be considered when looking at the knee.

- Andrew

I thought as much, never knew for sure. Thanks.

[FeRS]

Damper should be assembled soon and I'll hopefully have a dyno graph in the coming weeks.

[FeRS]

Another update. I learned some stuff today, most of it bad.




Here's the rod disassembled with the rebound and compressions stacks laid out. There was an ungodly amount of threadlocker on the end nut that took a blow torch to get off.





Here's the new digressive stack with Bilstein piston. I intended to have this assembled today, but I then ran into this:



The Bilstein 12mmID 46mmOD COB digressive piston is NOT the same size as the Megan Racing one. I confirmed with Megan beforehand that their pistons were 46mm, so someone has their measurements wrong.


I ended up putting on the Megan linear piston with my digressive shims as pictured above. I know you can make a linear piston act digressive with the right preload so that's the plan from here on out. Then in my infinite wisdom I put on the rubber seal cap and c-clip on the wrong end of the shock body.









These are next to impossible to take out, and I'm getting busy with IRL stuff so the next update on these might be a week or two. Gonna work on the GUI calculator in the mean time.

[Racecomp Engineering]

Did you get the 36mm Bilstein piston?

- Andrew

[FeRS]

Originally Posted by Racecomp Engineering

Did you get the 36mm Bilstein piston?

- Andrew

Nope, B-PI-COB-12/46 from RE Suspensions