Shorter rear springs for ERA rear suspension

wolf k · #1 (**permalink**) 06-26-2016, 09:19 AM

Can any one think of any pitfalls in installing shorter rear springs for the ERA designed rear suspension on my FIA? My desire is to lower rear ride height so that the rear tire gap to fender is reduced. I already have my coil overs adjusted to minimum ride height yet still have approximately 1 inch of fender gap. I am running 295/50/15 rear tires, using taller tires is not a good option for me.

DanEC · #2 (**permalink**) 06-26-2016, 10:15 AM

I think the FIA typically wheel well design had more wheel well to tire gap than the other models. If you have backed the stock springs off I would think your frame to road clearance is getting petty minimal. How much clearance do you have now?

wolf k · #3 (**permalink**) 06-26-2016, 04:21 PM

Rear frame to ground clearance is 5 inches, front is slightly less.

strictlypersonl · #4 (**permalink**) 06-27-2016, 06:17 AM

You've probably got our standard Eibach spring: 0900.225.0550. (9" Long x 550 lb/in). You could either go shorter (8" long) or use a lower rate, i.e. 475-500 lb/in. If you are using an aluminum-block engine, I would do the latter.

wolf k · #5 (**permalink**) 06-27-2016, 06:48 AM

Yes, have the standard spring, 9"x 550 lb/in, so I will go with the shorter spring same rate.
I do not remember the formula for lowering, 1 inch shorter spring lowers the car more than 1 inch? or less than 1 inch?

DanEC · #6 (**permalink**) 06-27-2016, 10:38 AM

Roughly you can take the dimensions from the lower control arm inside pivot to the tire center, and the lower control arm inside pivot to the shock absorber amount and calculate the ratio of the two. For example if the ratio is 1.5 then that can be multiplied by the difference in spring length (1 inch) which all things being equal (spring rate and so forth) would drop the rear 1.5 inches.

It's not exact but should be reasonably close with accurate dimensions and ratio. Since the 8 inch spring has a slightly lower spring rate the actual drop should be a little more.

wolf k · #7 (**permalink**) 07-04-2016, 05:59 AM

Top is factory ERA setup
Bottom is two inch shorter spring with a helper spring

Result

wolf k · #8 (**permalink**) 07-14-2016, 05:16 AM

Just wanted to post that the car rides great with this spring set-up, no ill effects. With the two inch shorter spring and helper spring, this places the adjusting ring in the upper 1/3 range of adjustment. With this setting, the tops of the tires are flush with the wheel opening.
I also have the front lowered as well so the top of the tires are flush, the stock length springs were suitable as there is much more adjustment range in the front shocks. However, I should install helper springs in the front also, to keep the springs loaded when the car is off the ground.