suspension springs


Staff member


engineguy posted this info

"There is a lot of difference in springs, whether OE replacement or aftermarket performance springs. Original equipment springs are designed basically to hold the vehicle at the proper ride height. Due to the fact that there are/were (usually) several engine options available, springs are designed to handle the various weights involved.

The difference between springs is usually two major features: The diameter of the spring material (referred to as "wire gauge") and the overall length of the spring material used in the spring. Springs are normally categorized by the number of pounds of force that it takes to compress the spring one inch. Hence a 200# spring means that a force of 200 lbs will compress the spring by 1".

If you compare two springs side-by-side and one spring has more coils that the other one, the spring with more coils is actually softer than the spring with fewer coils, assuming that the wire gauge is the same for both springs. To visualize this, consider the fact that a coil spring is actually a torsion bar that is wound into a circular shape. A short torsion bar will be more difficult to twist than a longer torsion bar, again assuming that the diameter of both bars are the same. A good example of this is rear coil springs. Observing rear coils for an El Camino or station wagon and you will notice that springs for these vehicles have fewer coils that the rear coil for a coupe or sedan. "

RB69SS396Conv posted this info
"There are probably 15 or 20 Moog part #s that will fit some cars, with a HUGE variety of free height and rate, and spec'ed for various installed heights and weights (which, since the car has "leverage" on the spring, is NOT the same as how much one corner of the car weighs).

As said, if you buy the "heavy duty with air" listing, it will sit up too high.

Best thing to do is look up the "standard" springs that the book shows; then compare the rate, free height, and installed height at whatever weight they give it for, for each of the other part #s that will physically interchange (same OD, similar wire dia, correct end shapes), and pick one out that gives the effect you want. For example if you want it to ride stiffer you might pick one that would work out to having a similar installed height at the installed weight that the book shows for your car, given its rate. E.g. if you find one that has an IH of 16" @ 1600# with a rate of 300 #/in, and then one with an IH of 15" @ 2000# with a rate of 400 #/in, then the stiffer one will sit at about the same height at your weight (1" higher than 15", at 400 # less than the 2000 # given), but will be noticeably stiffer. Or, if you want to raise or lower the whole car, you can apply the same principle. I wouldn't suggest straying too terribly far from the stock parameters though, if your springs are OE now, then even just the lamest stock replacement will be RADICALLY different. Not AT ALL like a direct swap-out."

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