Softer Coil Spring Rates

[Mr Nick]

My current combo is a bit on the stiff side, years ago when building this car my vision was cruiser during the week and casual autocross on the weekends. Well the reality is I use this car as a spirited cruiser and in 5 years have only auto-crossed once on a Hot Rod Power Tour stop.

I'm thinking of softening the suspension a little bit, currently it rides nice on smooth roads (of course) but it struggles to absorb impact from any type of quick/harsh bump on the road. Even at low speeds (driveway curbs for example) the car feels too stiff like it rocks over the curb, instead of the suspension absorbing it.

Front:
SPC upper and lower control arms w/tall upper and lower ball joints
UMI 4050F 530 lb rate springs
Spacers in driver LCA only to fix the lean
ridetech HQ single adjustable Fox shocks
Hellwig sway bar with poly end links
255/40/18



Rear:
UMI lower trailing arm, poly bushing on frame side & rod end on axle
UMI upper trailing arm, rod end on frame & rubber bushing in axle housing
Hypercoil 11" 175 lb rate springs
ridetech HQ single adjustable Fox shocks
Hellwig sway bar
285/40/18

The chart shows what UMI suggests when using coil-overs up front. Assuming this is also accurate for non coil-overs, then the 530 lb springs I have now are way too stiff for my small block Olds with alum heads & intake, lightweight battery and no heat or AC.




Also, UMI 2" drop rear springs are 135 lbs rate, again suggesting my current 175 lbs rear springs are too stiff.

I'm thinking of changing to 11" 150 lbs rear coils, will lower it a touch more and also ride a little softer. Then up front move to a 400 or 450 lb spring. I'm not opposed to switching to coil overs up front, but would rather not do coil overs in the rear since I just finished my exhaust and I really don't want to risk having to move it.

Thank you for any suggestions and comments.