help with spring rates

[skeevay]

I am trying to determine what rate springs to order for my 65 impala. I have done some research/estimating/guessing and come up with some numbers. I was hoping I could get some input from some of you with experience in this department.

I am guesstimating the total weight of the car to be 3900 lbs. 57%/front 43%/rear. Lt1 w/ alum. heads....T-56 trans. 4th gen camaro front suspension using coil overs. Motion ratio= .4 (13.75" lower A-arm/ 8.75" A-arm pivot to lower shock pivot) Shock angle of about 12 deg. 1 1/4" front sway bar. Rear suspension is truck arm with coil overs in factory spring location (on top of trailing arms ahead of axle housing). No rear sway bar. This car will be used mostly on the street and for road trips occassionally so a decent ride quality is desirable, although I do like the firm "sports car" feel.

700 lbs. in front/ 225 lbs. in. rear......? What do you guys think?

[sinned]

225 in the back is too much, especially for the type of ride you want. Rear spring rate has much more affect on ride quality than front rate does. I would stick with the 700lbs in the front but run no more than 160-175lbs in the rear.

[Orngcrush69]

I agree with dennis, 225 is way too much for the back. I'm running a BBC with alum. heads, 1 1/4 sway bar in the front and none in the rear and my rate are 800 front 175 in the rear, and I run this car hard on the track and then drive it home.

[BRIAN]

For a coil over I do not feel the 225's are a bad starting point. Use qa1 stuff they are accurate and have poly coating which makes them easy to clean and return if they are the wrong rate. Tell them the travel you are looking for in a shock and they will set you up pretty close. Most full body cars I have done wind up with between 175 to 250 with a 9 or 10" spring. Also take into account approx 1/2" of settle on quality springs.


Set up car, put on floor and then measure your springs loaded on the shocks. Keep the adjusters approx 1/2 up on the threads. If spring doesn't compress and allow shock to provide the travel you are looking for then adjust from there. Every shock has a set height that is should operate within.

[David Pozzi]

a 250 lb/in front rate at the wheel would be pretty nice. A 650 lb coil would yield that rate using a .4 motion ratio plus the coil angle.
Here are some calculators to help
http://www.proshocks.com/calcs/index.htm

[sinned]

Are these true coil overs or just truck arm springs with weight jacks...makes a huge difference?

[skeevay]

Thanks for all the input.

Are these true coil overs or just truck arm springs with weight jacks...makes a huge difference?

Coil overs. I'm leaning towards the QA1 dr5855p's. They have a suggested ride height of 13.25"-14.5" and that's right where I need to be.

a 250 lb/in front rate at the wheel would be pretty nice. A 650 lb coil would yield that rate using a .4 motion ratio plus the coil angle.
Here are some calculators to help

I used some calculators like that from another link (very helpful!), plus did some math with a calculator just to double check. I was coming up with about the same figure of about 250 lb. wheel rate. One thing is a little confusing in my research....When trying to find the spring rate for a certain wheel rate you must first plug in a spring rate to actually get the wheel rate. Does that make sense or am I just up too late?!

[aonghus]

I knew something was wrong when I received my package for my FRONT coil overs with 200lb Eibach 8" springs....