Join Date: Aug 2002
Location: At the apex, blocking your pass.
Most V8 Mustangs have a factory front spring rate somewhere around 425-450#/in. (Cobras were more softly sprung and got 400# springs.) That translates to a 118-125#/in coilover spring (111# for Cobras.) A 218# coilover in front equates to a 785# spring. (Are you sure it's 218 -- that's an odd rating -- coilovers are usually sold in 25# increments.)
In back, Most GT's got factory springs in the 200#/in range (Cobras got 165#/in.) This translates to a 110#/in coilover (90#/in for Cobras.) Your 123# coilovers (again, an odd rating for coilovers,) equates to a 224#/in spring.
You'll end up with a moderately stiffrer setup, similar to H&R race springs up front and between FMS (200#), Eibach (200# for Pro and Sport Kits), and H&R Sports (250#).
And if you "go wild" with the rear suspension, you're probably going to want a MUCH stiffer rear spring.
-- Robert King
NASA AI #42, Texas
Instructor, NASA Texas Region
Instructor, TWS Perf. Driving School