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Originally posted by RogerB:
And now for the science:
Cutting is generally not recommended because you don't really have much control over the final spring rate. With suspension travel reduced, you need a higher rate to avoid bottoming. Furthermore, there's no way to know for sure that the new rate will be properly matched to your strut choice. Still, in some shadetree applications, it might be your only option, and it might work OK if done properly.
Just playing the devil's advocate...but think of all the people that buy spring brand "x" and struts brand "y". DO they know if the 2 brands are matched? No.
So really that risk is apparent anytime you change springs or struts...even if you get OEM replacements from a generic company.
98 E0 SVT with some stuff
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Strut to spring matching doesn't matter that much. With the rates and uses we're discussing, it's moot. Yes, cutting the spring increases the rate. Originally posted by Buddy Palumbo:
I believe spring rate has to do with the spring's tensile strength and number of coil wraps per inch
All spring steel has very similar elastic properties. The rate of a spring can be determined by # of wraps, coil diameter, and wire diameter. Free length has a minor effect.
Buddy, if it was just # of wraps/unit length, then what would be the rate of two 500lb/in springs put end-to-end? 500lb/in, of course. But that's obviously not right, since stacking two 500lb/in springs will give you a 250lb/in rate. It's proportional to the number of coils.
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Originally posted by Big Jim:
Originally posted by Buddy Palumbo:
Originally posted by RogerB:
Cutting a spring will increase the spring rate, since "length" (or rather, "number of active coils") is part of the rate equation.
I don't know if this is a true statement . I believe spring rate has to do with the spring's tensile strength and number of coil wraps per inch (or foot , or whatever) . I think if you cut a spring , it's spring rate will be the same , but over less travel length .
Also, some springs have a linear spring rate , having an even number of wraps throughout the spring (like Eibach , IIRC) , whereas the springs I'm running (H&R's) have a progressive spring rate , where the springs start out with a certain number of wraps & then get closer together . Coilovers are a linear rate spring , are they not ?? Ones that I've seen in person have been .
I question that as well.
When I was in high school, it was a common thing to heat the front springs for the "raked" look. I even observed it done a few times. Every one of the ones I was aware of had horable ride quality after torching the springs. The springs most certainly not only lost the ability to hold the car at original height, but also bounced all over the road.
Just my observations.
Handy Spring Rate Calculator
Now, I could be wrong, in that heating the spring enough to change its shape might affect the modulus...
Function before fashion.
'96 Contour SE
"Toss the Contour into a corner, and it's as easy to catch as a softball thrown by a preschooler." -Edmunds, 1998
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The modulus won't change. It's a constant for any given alloy. Even within different kinds of steel, it's very close: within a few percent.
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I hope you are not trying to say that temper doesn't effect spring character. Heating a spring until it sags without much or any proper attempt to retemper it really screws up a spring. Just spraying cold water on it while it is still hot isn't enough.
Jim Johnson
98 SVT
03 Escape Limited
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The modulous will not change. The problem is that you'll get plastic deformation (sag) in the spring if you don't heat-treat it properly.
Anyway, heating springs is stupid these days. If you do it very carefully, it can work. But, it's not worth the time, materials, and training when you can get cheap imported springs that will work just as well for so little money.
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Originally posted by Auto-X Fil:
Strut to spring matching doesn't matter that much. With the rates and uses we're discussing, it's moot.
Yes, cutting the spring increases the rate. Originally posted by Buddy Palumbo:
I believe spring rate has to do with the spring's tensile strength and number of coil wraps per inch
All spring steel has very similar elastic properties. The rate of a spring can be determined by # of wraps, coil diameter, and wire diameter. Free length has a minor effect.
Buddy, if it was just # of wraps/unit length, then what would be the rate of two 500lb/in springs put end-to-end? 500lb/in, of course. But that's obviously not right, since stacking two 500lb/in springs will give you a 250lb/in rate. It's proportional to the number of coils.
I don't think I picked my words correctly , or maybe you misunderstood me . I realize what you're saying about stacking 2 springs & whatnot . However , I still stand by my thoughts about tensile strength , wire size/diameter & progressive # of wraps for a progressive spring rate . Just me thinking aloud ...
~~~~~~~ Phil 
Black & Tan 2000 SVT Contour #2137 of 2150
35,000 miles & counting !
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Let me phrase it simply, to be sure we are on the same page:
If you cut ANY apring, it's rate will increase.
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