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PCA Member since 1988
Join Date: Feb 2018
Location: SW Washington State
Posts: 4,638
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The way dual springs like that are "supposed" to work:
The two springs together have a lower total spring rate than either spring alone, as Bill described. BUT, if properly designed, the shorter spring with lower rate spring should "coil bind" before the suspension hits its bump stops, at which point the remaining spring rate takes over. In practice, this is difficult to achieve, because the travel and ride height must be precisely known (which also means no more fiddling with the ride height afterwards).
Thus, springs can be selected to give a certain amount of travel with both springs working, before the weaker spring hits coil bind, and then the stiffer spring rate prevails, until the shock/strut hits the bump stop rubber, which increases the spring rate even further.
If your supplier doesn't specify these parameters, then you can be pretty sure they are just guessing. I have yet to see the usual suspension vendors provide these details. (edit) Therefore, I suspect most of them are selling appearance over function.
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1973.5 911T with RoW 1980 SC CIS stroked to 3.2, 10:1 Mahle Sport p/c's, TBC exhaust ports, M1 cams, SSI's. RSR bushings & adj spring plates, Koni Sports, 21/26mm T-bars, stock swaybars, 16x7 Fuchs w Michelin Pilot Sport A/S 3+, 205/55-16 at all 4 corners.
Cars are for driving. If you want art, get something you can hang on the wall!
Last edited by PeteKz; 05-16-2025 at 04:34 PM..
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