Odd ball spring question

Phil1098

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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?
 

RocketcarX

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There is no room to have a legit coil over in the rear, so you get an adjustable spring perch and smallish diameter spring. A lot of platforms do this .
 

Wes06

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no hes asking why coil over setups tend to have really tightly wound diameter springs up front rather than larger diameter such as stock or non coilover replacements
 

Norm Peterson

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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
 
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Phil1098

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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

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?
 

Norm Peterson

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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?
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).

Coilover springs come in a wide range of rates and free lengths, with rate increments of 50 lb/in or smaller in many cases. There's more, but that's the basic stuff. Google Hypercoil and look inside their catalog.


Norm
 

Sky Render

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Coil overs use smaller springs because most spring manufacturers make springs in that diameter. It allows easy adjustment of spring rate by swapping springs. So Eibach can make one set of 800-lb springs that would work on a vast majority of coil overs on the market, for instance.

If your coil overs used the same diameter ​spring as stock, you'd have to find springs in that oddball diameter to change rates.
 

SoundGuyDave

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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.
 

Phil1098

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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.

You are 100% correct, that is what I was asking. Your answer seems solid to me. Maybe they do small coils in the rear stock just because of space limitations and are forced to spend a few extra dimes.
 

kerrynzl

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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'll chime in here [as a first posting].
Two things are advantages.

Firstly the smaller diameter allows for larger tyres,
Secondly the tighter the winding , the stiffer the spring.

You need to picture a coil as a wound up torsion bar, the shorter the bar [or spring] the stiffer it is.

Now the downside [which is why OEM use larger wound springs]
A tighter spring has less spring load for the same given stiffness so it will come out of the spring lands when the load comes off.

Because of this, OEM springs can also be mounted above the tyre height.
 

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