Rear track-width changes

[Blown_xa]

widening just the rear track width will cause your car to understeer more than is does already. You should keep it the same width front and rear if not wider in the front. Increasing track width over-all will make the car more stable, but also you are extending the leverage point of the suspension therefore softening your spring rate in a sense. If you understand suspension and handling characteristics and how to adjust them, then you can come up with a killer handling car.

I use 20mm spacers in the front and 10mm in the rear.
I set up my car for slight oversteer steady state.
Also in my set up to acheive that includes:
Progress Coil-overs with 200 pound springs in the rear, 450 in the front.
Progress rear sway, stock front sway (soon to be omitted)
-2.6 degree front camber, 0 toe
-1.1 degree rear camber, .40 degree toe in(per)-rear toe in helps with stability on high speed road coarses with short wheelbase, probably run less for auto cross.
Tires are everything, you can have $6000 coil-overs and a guy with stock suspension but with better tires will beat you...
I run Toyo R1R's 225 50 15's all around
28psi cold front
33psi cold rear

just suggestions but at least you have something to go by.