Theres a formula available to help determine required spring rates..but thats just a starting point..may havve to bump up and down a few numbers to aquire the exact "feel"
your looking for...
http://www.ridetech.com/info/spring-rate-calculator/

 

Okay, I knew I should have deleted that comment from my post. I have seen innovation here. Not looking to get flamed......just trying to get some info out there from an unexpected source. Hope it helps someone.
Thanks, Ray in TX.

 

Also, for my Fiero, I found the factory spring rates posted on one of the Fiero forum threads and went from there. The 250lb/in on my original rear struts worked fine. Just a little stiffer than factory spring rates. I went to the 300lb/in springs 'cause I have a 3800na Buick engine w/4spd automatic that I'm going to install soon.
Thanks, Ray in TX.

 

Not "knocking the SS guys". I am an SS guy! (and a Fiero guy) I've gotten lots of good info on here. Lots of sharp people with good ideas. I guess I'm just used to seeing more fabrication and innovation on the Fiero forum 'cause we're dealing with an older design, and parts that are becoming harder to find. Just trying to inject some ideas on the coil overs.
Thanks, Ray in TX.
2009 HHR SS, Aqua Blue Metallic, Automatic, AA5 option, Trifecta Infiniboost ~24psi peak(cruise controlled), Forge Motorsports BPV(yellow spring installed), K&N drop in filter, Dejon charge pipe, TTR sway bar, TTR upper engine mount, MPX catless downpipe, EBC redstuff front pads, Moog front sway bar links, Dunlop SP Sport 01 DSST - 245/40R18 93Y.

 

Moon, you put the fatty's on there yet, I am going to try my 265x40 on the rear, see if that .4" will clear the fender liners.

 

SS fan: Just got them on a couple hours ago. they fill up the wheelwells real nice, and seem to stick much better than OE's. They are aired up to [gulp] 44 lbs., so after I put a couple of heat cycles in em, will drop them to 32 lbs., and they should stick even better. So far, so good.
They are Handkook Venus V12's, 255-40-18's, and rated perry high for dry traction. Autocross next month ought to be much better, with the trick coilovers, and sticky tires. "Moon"

 

I think the 255's are wide enough, I will be installing the Brembos and new rear matching rotors and pads, with the KW's in the morning, I want to come play at the track too !!!