i have a 2002 Gt, i want to lower it 1.5 all the way around, i got the 315's in the back and i just want suggestions on the type of spring i should get.. like whats the difference between progressive and not? BBK Performance 2501 - BBK Gripp Lowering Coil Springs - Overview - SummitRacing.com im looking at those, but let me know if im in the wrong direction or not, thanks for any help!