School me on suspension

[Boschwillkillyou]

I'm new. I just picked up a 91 318is and I'm wondering if all lowering springs are interchangeable for all e30s?
I'd have to assume that if you put the same springs on a 325 it'd be lower than a 318.
Also, if the PO of my car put Billstien sports in with the stock springs would I still need to change them if I put some lowering springs on?

[jlevie]

A 318 and a 325 need different springs. If the shocks haven't been on the car too long, and are thus worn, you can re-use them.

[JoeyBones]

to expand, the reason for the different springs, is the different rates due to weight of the vehicle. The 6-cyl engine in the 325 weighs more. The same springs will physically fit however in a pinch...