The original question (accidentally erased) was if a progressive coilover could be made cheaply at home, perhaps using a Ground Control kit with two different sized springs or whatever.
The original question (accidentally erased) was if a progressive coilover could be made cheaply at home, perhaps using a Ground Control kit with two different sized springs or whatever.
It sounds to me like you'd just need a little motor on each damper to turn the adjuster when you flip a switch or turn a knob inside the car. The B16 setup sounds a lot like the tein electric damper force controller.
Lol, ok. I was referring to the type that has two different sized coils on each damper.
Call ground control. I think they offer all of the parts to build the exact setup you want. I'm sure they can explain what damper they think you need.
AFCO certainly has the parts and there's some good tech on their site. There are a couple of interesting things you can do, including keeping the soft spring inactive at ride height and only having it come into play beyond a chosen amount of droop. Spring rates interplay as well.
The real question is - just what are you trying to achieve?
Eibach has a nice calculator, or at least the formulas, to calculate the combined spring rate, resting length, and the length where the softer spring get's bound up and the spring rate reverts to the stiffer spring.
I used the formulas extensively to design a nice package with some custom aluminum Bilstein shocks.
Thanks for the info, everyone.
Keith, I was considering them for two different cars; a full bodied 1300 lb. home built and a 2400 lb. EP3. Both streetable with occasional Track Days capabilities. But still somewhat comfortable on the street.
An analogy would be to have a tire stickier than Azenies but comfortable on the street. Such as the Kuhmo XS. Not quite a track tire but doable. A compromise but a good one.
Since cost is a big factor for me, the idea intrigued me. If I could afford it, the Honda would have custom Bilstein B16s. There's a guy in Germany that I've been communicating with and he uses them on the 'Ring and for dd and loves them.
It's been my experience that the quality of the shock and the suitability of the damping has a bigger effect on both ride and performance than the spring rate does. I would expect a progressive rate spring (whether it's from how the spring is wound or a dual spring setup) would lead to changes in the car's handling as the suspension compresses - and that if you were using twin springs, you'd see a step change in spring rate when the soft one hits coil bind. Never tried it though.
I know one of my AFCO books has some interesting info on applications of a dual spring setup, in the idealized situation of a car that only turns left 
I'll see if I can dig it up.
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