Looks like you're in uncharted territory. We did have a Focus ST run in 2013, but we invited him from the SEMA Show floor, so he probably didn't put much thought into suspension modifications. Good luck and I'll see you in Vegas!

Jim McIlvaine
eCare Manager, OPTIMA Batteries

 

So you are just looking for a custom spring then? Have you tried reaching out to some of the spring manufacturers directly to ask for a custom spec ID, length and rate specifically vs just finding off the shelf ones?

Alternatively, have you looked at rear coilovers? Those have adjustible rear seat perches that attach to the lower control arms and then some have alternative spring options. Like my Fortune Auto coilovers let you select rates from 4k-28 as an add on using Swift springs. 450# is the equivalent to 8k
Fortune Auto 500 Series Coilovers for Ford Focus ST - Fortune Auto SuperStore by Enjuku Racing Parts, LLC

Then on my other focus that I ran K-sports, i wanted a stiffer rear spring so i wouldnt rub as much when going super low with my lower offset wheels. I was able to contact them and they sold me a 9k spring to replace my stock 6k rates. Seemed springs in different rates are easier to come by with a coilover setup.

 

Thanks for giving this some thought guys. Since the goal with the suspension is excellent handling; I am not keen on the systems that change the mounting location of the springs. In my opinion the car is not designed to carry its weight anywhere but the factory location unless significant fabrication and reinforcement is done.

I think I have come up with a solution utilizing some aftermarket Honda Civic lower spring perches of the correct dimensions. My plan is to fit these through the holes in the bottom of the control arms and pinch them in there with the provided locking rings.

 

The picture you are using is showing the same looking lower perches that I mentioned coilovers come with. Rear coilovers do not change the location of where the spring is, unless you are referencing that you can adjust the ride height with them thus changing where the spring technically is...again, this looks like what you have in your picture. The ones i have used on focus sit in the perch and are usually secured with a bolt and large washer through the bottom

I would assume any class of racing that doesnt require stock suspension would be utilizing coilovers for their ability to set custom dampening/rebounding and corning balancing.

Either way, glad you found a solution