Originally Posted by

**robmac**
**Coil Spring Rate Formula:**

11,250,000 - Torsional Modules For Steel (Constant)

**CSPWD** - Coil Spring Wire Diameter (How thick is the wire?)

**8 **- Constant

**NOAC **- Number Of Active Coils (Coils that are free to move. Not coils seated. It may be that 1/2 of the top and bottom coil is seated causing a spring with 8 coils to have the distance of 7 free.)

**CMD **- Coil Mean Diameter (The diameter from center to center of the coil. Measure the diameter of the coil from wire center to wire center. If you know the coil is .5 inches thick and the outside diameter of the coil spring is 3 inches, then the Coil Mean Diameter would be 2.5 inches)

(11,250,000 x (CSWD x 4))

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(8 x NOAC x (CMD x 3))

All Measurements in inches -

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404 Valve spring = 30.5 lbs/inch

404 Prop Shaft spring = 18.75 lbs/inch

18.5 / 30.5 = 0.6 near enough to 2/3 !