Who makes the lowest spring for the Z? I believe it's either Eibach Sportline or GF210's? Correct me if I'm wrong?!

 

You are one hundred percent correct.

 

Sportline is the lowest before getting into coilovers correct?

 

^ yes

 

Technically the lowest is Sprint at 1.75"/1.75"

IMO, if you have to go that low, your better off with a coilover system so you can hopefully actually have some shock travel. For that reason I've never included the spring in any of the aftermarket suspension lists I publish

Some other choices mentioned and not mentioned.

H&R sport progressive springs 350Z 1.3”/1” drop
Spring rates in LBS 370/400 (peak rates only, softer initial rates are unknown)

Eibach 350Z sportline progressive springs 1.2"/1.2"
F: 239/400 R: 257/435

Tanabe GF210 Series 350Z progressive springs 1”/1.2”
Spring rates in LBS 336/375 (only peak rates are published, softer initial progressive rates unknown)

Kg/mm DRacing progressive springs 1.2”/1.2”
Spring rates in LBS initial/final front 252/454 initial/final rear 252/482 rear
^too much for oem shocks, Tokico D-spec would be fine

Swift 350Z Spec-R progressive springs 1.2”/1”
Spring rates in LBS initial/final Front: 291/392 Rear: 280/448

 

get sportlines and do the spring mount mod.