Spring Rate to Damper Ratios???

[Duk]

What sort of information do I need to help determine damper rates for a known spring rate?

Bilstein shocks quoted with numbers like:
40/20 210-120 Dampening or
60/20 320-120 Dampening or
30/50 160-260 Dampening.

Here says:
Understanding Bilstein Valve Ratings
Damping forces of Bilstein valvings for Off-Road are measured in Newtons at a velocity of 0.52 meters/seconds (approximately 20 inches/second). The ratings shown correspond to those measurements; rebound force is the first number, followed by compression force (rebound / compression). Conventionally, the ratings are written as one tenth the damping force in Newtons.
EXAMPLE: Valve rating: 275 / 78
Rebound force is 2750 Newtons at 0.52 m/s
Compression force is 780 Newtons at 0.52 m/s
Higher numbers mean higher (firmer) damping forces. For example, 360/80 has more control (is firmer) that 275/78, while 170/60 has less control (is softer) than 275/78.

10 Newtons = 2.248 pounds force.

I'm using a spring with 375lb/in rate.

[Ken_T]

I can't be bothered 'splainin' so I drew a picture.


What car? Coilover/motion ratio of spring same as damper? Primary use?

Damping coefficients in the low speed area should be between 0.45 to 0.7 for best handling and almost plateau off after that. Those numbers aren't going to tell you anything, especially because only off roaders damper pistons move that fast. They run progressive damping so it gets 'harder' so the car doesn't bottom out on landing where asphalt cars will run digressive damping so any bumps in the road don't upset the car too much.

Really need a PROPER dyno plot (constant velocity, force vs velocity) to see if the damper will suit your car. Then again I'm being super picky and trying to get it 100% right when it doesn't need to be anywhere near that to have fun.

[Duk]

What car? Coilover/motion ratio of spring same as damper? Primary use?

Car is non-Toyota.
Coilover MR is the same as the spring for the front. Haven't calculated for the rear yet.
Primary use is for the road.

Damping coefficients in the low speed area should be between 0.45 to 0.7 for best handling and almost plateau off after that. Those numbers aren't going to tell you anything, especially because only off roaders damper pistons move that fast.

Ahhh, so any suggestions for actual shaft/piston speeds for normal road car use? How can the reduced shaft/piston speed be converted to Bilstein's 0.52m/sec reference speed, or is that next to impossible without a shock dyno?
Where I am stuck is converting Bilstein 'X' Newtons of force at 0.52m/sec into something that would at least be a starting point for my (front) spring rate (375lb/in = 1668.15N/in = 65675N/m).

They run progressive damping so it gets 'harder' so the car doesn't bottom out on landing where asphalt cars will run digressive damping so any bumps in the road don't upset the car too much.

I really want to use a digressive valved shock to maintain ride and control when negotiating a decent bump, while having good bump valving to help make the car responsive. If road cars have lower shock speeds, are the digressive valved Bilsteins that are marketed for things like sprint cars no use?
I think I need to know a lot more or just modify my existing Koni's for adjustable bump valving. Not a real fan of the Koni's tho.

+ Repness for your input.

[Ken_T]

Ahhh, so any suggestions for actual shaft/piston speeds for normal road car use?

They say body roll moves the shock between 0-3"/sec (as per my MSpaint drawing), anything above that up to 10-12"/sec will be for handling bumps in the road.

How can the reduced shaft/piston speed be converted to Bilstein's 0.52m/sec reference speed, or is that next to impossible without a shock dyno?
Where I am stuck is converting Bilstein 'X' Newtons of force at 0.52m/sec into something that would at least be a starting point for my (front) spring rate (375lb/in = 1668.15N/in = 65675N/m).

Yeah, you can't do this. All you can do is ask bilstein to send you a plot of what the shock does, doubt they'd do that though. One shop gets bilsteins custom valved for it's application but even they don't have the plot for the damper. I asked the guy to get me a dyno plot because I'm not buying them without one and all I get is something like, "everyone that's driven the car says it's good". You should be able to email the tech guy at bilstein with your requirement and have them recommend a damper for the application. I know a member here did the same with koni and got some shocks recommended for him. They did tell him to get 8611-1259/8610-1437 which are probably good enough for what you want. I have dyno plots of these if you wanna see them.

And another thing, not saying bilstein do this but, one shock that was dynoed had a nicer plot (hard in the low range plateauing off nicely) in the softer end of adjustment than at the hard end where low speed damping decreased and the high speed increased. Totally backwards of what you want.

I really want to use a digressive valved shock to maintain ride and control when negotiating a decent bump, while having good bump valving to help make the car responsive. If road cars have lower shock speeds, are the digressive valved Bilsteins that are marketed for things like sprint cars no use?

I have no idea what a sprint car shock looks like and whether you can make it fit your app. If it does fit it's probably going to be too soft as I'm going to guess those cars are light and run soft springs. It might do though, The front are mounted half way up the LCA? and probably still have 5" of travel where they are.

I think I need to know a lot more or just modify my existing Koni's for adjustable bump valving. Not a real fan of the Koni's tho.

I have a bunch of pdf's and saved web pages on determining ideal damper rates if you want to read them. They get real complicated to the point of wanting to give up on getting 100% ideal shocks and just drive with what you have already. Which is where I'm at and I'm too cheap to want a 100% car.

Why not just buy double adjustable konis such as the 8611-1259. What's wrong with the koni's? twin-tube design or the inconsistencies between some shocks?

Also, have a look at QA-1. They have shocks which you can valve yourself. I can't remember if they started doing cartridge type shocks for mac' strut though.

[Duk]

I have no idea what a sprint car shock looks like and whether you can make it fit your app. If it does fit it's probably going to be too soft as I'm going to guess those cars are light and run soft springs. It might do though, The front are mounted half way up the LCA? and probably still have 5" of travel where they are.

They are a small bodied (1.875" with a 36mm piston) shock that measure about the same as the Koni's currently on the car.

Why not just buy double adjustable konis such as the 8611-1259. What's wrong with the koni's? twin-tube design or the inconsistencies between some shocks?

I have also thought about trying to add bump valve adjustment and an over pressure relief valve to try and achieve a similar effect to the Bilstein digressive valve effect. The problem I found with the Koni's is poor initial bump support for low speed transitional stuff, but that is contradicted by over damped bump valving. Hit a decent bump at speed and it does its best impersonation of a brick (I reckon that this is a result of Koni trying to provide a sporting shock for what was a severely under sprung car) . I think that if it was a high pressure gas shock rather than the low pressure gas twin tube, the initial bump support would be much better even with less bump valving.
Perhaps adding a floating piston between the inner and outer tubes and make it a high pressure gas shock

[Ken_T]

http://www.honda-tech.com/showthread.php?t=2415915
Dunno how much support there is for 36mm stuff but looks like fun.

Instead of putting on adjusters which are probably non-linear and not the same across two dampers, I think you're better off just getting a non-adjustable shock valved or valving a shock for your app.