I have seen it mentioned a few times that the rear OEM springs are standard 5"x13" springs, and can be replaced with Eibach ERS 5"x(whatever length your want) springs. What I have not seen are any pictures. Nor have I seen anyone say they have actually done it.

So, I took off one of the OEM rear springs, and the inside diameter appears to be approximately 3 7/8" or 3 15/16" (did not use a micrometer). Since Eibach ERS 5" springs are supposed to have a 5" inside diameter, it does not look like they would fit properly.

So, is anyone actually running the Eibach ERS 5" ID springs in the rear, and if so, what did you do to make them work?

 

Nobody? Darn.

 

im also interested.. would you be running it with a height adjuster? some one chime in please

 

5" inside diameter will work, but 5.5" outside diameter is a better choice.

As delivered the springs have a flat top and bottom. That works fine with the rubber oem upper spring seat, but will not work for the lower control arm. You will need to cut off enough of one end of the spring as to create your own "pigtail". Basically you'd be cutting off enough to mirror the oem spring.

Trick here is to pick the right free length to get your ride height right. Selecting the proper spring rate is just as important. Cutting up to .8" off the upper spring seat or back filling above it to gain as much as .6" is a choice to fine tune things height wise.

Zeal, Truechoice and Stance all offer adjustable rear spring seats for a price, which would go a long way towards taking the guessing out of where you would end up ride height wise. (Only thing I've ever seen from stance unfotuneately came with 616lbs rear springs).

 

Oh yeah, Kw and Bilstein coilover kits can be converted to a ERS linear spring by making a simple adaptor. (and avoid costly adjustable seats from someone else).

 

Have you seen this actually fit? The measurements I found don't seem to support it, but I could be wrong.

The Stance OEM rear upper spring perch apparently has a 5.0" outside diameter, so a 5.5" ID spring would not even engage/touch that spring perch.

The OEM spring bucket is cast to fit the rubber insert that the spring sits on top of. Then the aluminum spring bucket has a lip that would appear to interfere with a spring that was more than a half inch wider in diameter than stock.

What am I missing?

 

Well here's the problem. Since we are dealing with outside diameter, that demension is controlled. At you increase the spring rate of the 5" outside diameter spring, it's wire diameter goes up and the inside diameter shrinks. A 5" OD spring with 450lbs in rate, barely fits around the upper spring seat cone and will barely slip into the lower seat that fits in the lower control arm. Switching to 5.5" O.D. gives you the breathing room you have to have on the inside. Sorry, I knew their was a reason, I had forgotten exactly what it was until now.

 

Ah! I did not realize that they measured inside diameter on the 2"/2.25"/2.5" springs, but used outside diameter on the 5"/5.5" springs.
Thanks.

 

I was curious, so I called Eibach to get the exact dimensions...
The 9.5" x 5.5" OD - 500 lb/in springs have in ID of 4.24"
The 9.5" x 5.5" OD - 600 lb/in springs have in ID of 4.2"

Hypercoils
The 9.5" x 5.5" OD - 500 lb/in springs have in ID of 4.31"
The 9.5" x 5.5" OD - 600 lb/in springs have in ID of 4.24"

 

I realize this thread is 2+ years old, but searching on this site is terrible so im adding this to this thread for documentation purposes.

https://my350z.com/forum/10071325-post77.html