Dougs951S

That depends what tires/sway bars/alignment you run, and what type of handling characteristics you want from the car. If you have a stiff front sway bar, you'll want a bit more rear spring so I would recommend 650's.

jmj951

Currently, I have a 26.8mm front bar and a 19mm 5-way adjustable rear bar, which I need to keep on the softest setting on the track due to all of the quick direction changes in parts of the course. Before I upgraded the rear bar, it was a very good balance, but the rear of the car was really sloppy (inside way up, outside quite a bit lower) getting into the corkscrew. Now, the rear is level, but unfortunately I can break the rear end loose with ease.

I run a little toe-out on the track. 8.5" front wheels, 10" rears.

Dougs951S

My current springs are 8" and obviously 400# springs will compress 33% less than 300's. Will I be able to get away with using a 9 inch spring in the front? I can get a good deal on a set of 400 lb 2.5 x 9 springs. My car is currently fairly low, think "just high enough to be usable on the street-low." I'm hoping as an added benefit the added stiffness will keep me from catching the underside of the car against the pavement over really rough bumps. Every once in a blue moon I hear it just barely kiss.