Need Help! Changing Rear Chassis Springs

[John A. Simpson]

I'm plagiarizing Herb Adams book 'Chassis Engineering' here but to get you started if your springs are rated at 300 lbs-in. then when you compress the spring one inch it will support 300 lbs. If you compress another inch it will support another 300 lbs. for a total of 600 lbs. Your spring compressed three inches can support 900 lbs. Your coil-overs are close enough to vertical it shouldn't be a big factor. If your know your sprung weight you can get close. If your sprung weight, basically what you're picking up with your jack when you were taking the weight off yours springs but not lifting the differential etc., you can figure it out. If your sprung weight is 1200 lbs. you'd need 1200 lbs. of spring load to support the car at rest. Each spring will be compressed two inches to support your hypothetical 1200 lbs. So I'm guessing IF (big if) in this example if you put the car two inches above your desired ride height and had the coil-overs collars snugged up to the spring, you would be close. Do you know the weight of the rear half of your car? I'll bet you can figure it out from watching what your current springs do. For example, if your 240 lbs-in. springs compress 2.5 inches (to support 1/2 of our theoretical 1200 lbs. )the 300 lbs-in. springs would compress 2 inches. I think if you measure and watch your springs you can get pretty close, but I have to admit this is all arm chair theory on my part, I have NO experience. Good Luck young Skywalker. If nothing else if I'm completely out of the ballpark maybe someone who really knows will chime in. I sounded pretty good though didn't I.



John