Phil1098
Member
This doesn't really matter much, but does anyone know why coil over kits have small front springs (that look mostly like rear) and a traditional front strut has way larger diameter windings?
Holding everything else constant (wire diameter, number of coils, material, etc.) the larger you make the mean spring diameter the softer the rate becomes. Plus the spring gets heavier because there's more wire in it, and it'd get heavier still if you were to try to recover the lost rate. Racing and performance in general prefer springs to be relatively stiff and light as opposed to soft and heavy.
Spring rate formula (big mean coil diameter - cubed - in the denominator makes the stiffness get smaller fairly rapidly):
Rate = [Shear Modulus] x [Wire Diameter]^4 ÷ 8 x [Number of Active Coils] x [Mean Coil Diameter]^3
Norm
My guess as to why the OE's use "big springs" (a term perhaps common to circle track) is tied to material grade (i.e. cost) and energy per unit volume (deals with durability with lower values for energy per unit volume permitting less expensive material).Understand and agree completely, it still doesn't make much sense. There are coil over kits that ride like stock, yet stock has the great big springs. You never see a coil over that uses big springs, yet they are both holding up the same mass and doing the same job. Or am I looking at this completely wrong and coil overs are track only and too stiff for the street?
I think the question he's asking is "why small diameter springs, not large diameter?"
For coilovers, which are a true motorsports application, the answer comes down to packaging. Smaller is always better, as it allows more clearance for suspension components, wheel width, tire sidewall, brake rotors, etc.
For OE's, they can have a larger margin of error in the spring, since the larger diameter is less sensitive to things like variance in metalurgy, wire diameter, or heat-treating. In other words, it's cheaper to do the larger spring.
I think the question he's asking is "why small diameter springs, not large diameter?"
For coilovers, which are a true motorsports application, the answer comes down to packaging. Smaller is always better, as it allows more clearance for suspension components, wheel width, tire sidewall, brake rotors, etc.
For OE's, they can have a larger margin of error in the spring, since the larger diameter is less sensitive to things like variance in metalurgy, wire diameter, or heat-treating. In other words, it's cheaper to do the larger spring.