I have all sorts of books and charts that can predict the spring rate of a coil, leaf or torsion bar, none cover air springs. Given the numbers from Firestone, they would be highly progressive rate.
OK fellas - that's great info but it doesn't help me solve my problem. Steve says the ***umption is that the spring is half way between the control arm attachments and the ball joint attachment. What if it's only 40% of the distance to the ball joint? The psi required to lift the car the same length of travel goes up right? What's the math for that? I used Slam Specialties charts and ordered what looked like the right size (RE-6's) but I have to go to 115 to 125 psi to get them to rise to drive height and the ride is very harsh. My solution would be to move the lower bag mount further toward the ball joint - right? In my case my measurements show I can mount hand fabricated brackets with an 11 degree cant toward the lower ball joint before I run into a clearance problem. Does that make sense? FYI the car weighs 3840 lbs and I am running a 76 Malibu front clip.
Moonglow2, Yes the farther out you move the bag tward the ball joint the easier it will be to lift the car. Many people who make thier own brackets weld the upper cups to the plate about 1 inch outward especially on 58-64 Impala's because there is plenty of room in the frame opening. If it were me I would change out to a RE-7 and move the bag outwards 1/2 inch to 1 inch on the lower arm and I would bet your ride height PSI will drop to around 70-80 which would make for a smoother ride. RE-6 are not really good for a car that heavy in the front. The RE-6 would work great in back cause by my guess your car is probably close to a 60-40 split on weight over the axle.
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