Which springs for coilovers

[w793_2000]

Which rear coilover springs do I need for a 68 Camaro super gas car if I don't have access to 4 wheel scales? The car weighs 2680, rear halfed with Alston chassis kit.

[Jimmy Smith]

My thoughts would be 130. Later J.Smith 4621racing

[w793_2000]

Thanx for your thoughts, Jimmy. Been searching though and it looks more like #110 to me. Anyone else have any ideas? Also, does anyone know if there's a way to identify my old springs if they aren't marked? By wire diameter maybe? They mike out at .396........Mike

[jim hensley]

mine was set up with 120# that is what santhuff recommended.

[Michael Pliska]

Are your shocks in front of or behind the axle? That will affect the desired spring rate as well as the overall rear weight. How much engine setback do you have from stock?

As far as determining the spring rate, you need the wire diameter, the coil average diameter (which you can calculate from the coil OD and the wire diameter), and the number of "active" coils. For active coils you just need to start on one end at the point where the coil last touches the coil next to it, then count the number of turns until you hit the comparable spot on the other end (may not necessarily be a whole number, could be 11.5 coils for example). If you want to post that info, I can calculate it for you. Or if you want to do it yourself here is the formula:
Rate (lb/in) = Gd^4/8ND^3
G=11.25E6 (torsional modulus for steel) 11250000
d=wire diam in inches
N=# of active coils
D=mean coil dia in inches

Incidentally, my Vega with some ballast and an iron headed BBC is close to your weight, with the shocks in front of the axle. It seemed to like 90-110 lb springs the best.

[Mike Pearson]

Originally Posted by Michael Pliska

Are your shocks in front of or behind the axle? That will affect the desired spring rate as well as the overall rear weight. How much engine setback do you have from stock?

As far as determining the spring rate, you need the wire diameter, the coil average diameter (which you can calculate from the coil OD and the wire diameter), and the number of "active" coils. For active coils you just need to start on one end at the point where the coil last touches the coil next to it, then count the number of turns until you hit the comparable spot on the other end (may not necessarily be a whole number, could be 11.5 coils for example). If you want to post that info, I can calculate it for you. Or if you want to do it yourself here is the formula:
Rate (lb/in) = Gd^4/8ND^3
G=11.25E6 (torsional modulus for steel) 11250000
d=wire diam in inches
N=# of active coils
D=mean coil dia in inches

Incidentally, my Vega with some ballast and an iron headed BBC is close to your weight, with the shocks in front of the axle. It seemed to like 90-110 lb springs the best.

I would say this is more correct. I have 130 lb springs on my car and it weighs 3200 lbs. Hal Lee recommended 110 on my car But I have not tried them yet