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Coil Springs

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Our coil springs came from Poly Performance, and we opted for a 12x3x450 over a 12x3x500. Our upper spring is 12 inches long, 3-inch ID, and 450 lb/in; the lower is identical but 500 lb/in. The combined spring rate is equal to the top rate times the bottom rate divided by the top rate plus the bottom rate [CR = (TR x BR) diviede by (TR BR)]. This gave us a combined rate of 237 lb/in.