Question about cutting springs

[jackr]

If you cut 2" off a spring, will that result in lowering the car 2" or is there some other geometry involved?

Thanks
Jack

[George Willet]

In a nutshell, NO! There are many variables: front or rear? what was the rate of the spring to begin with? what is the motion ratio of the suspension? Cutting springs is false economy if one doesn't have the ways to figure the end result.

Advise looking at Centerline's springs. They are inexpensive, and they work. Or Steve Smith's "Acvanced Race Car Suspension Development" book is only $20. or so, and one can find the ways to see how things interrelate, and how do what you want.

Hope this helps, George

[Chris Kattchee]

Jack,

It's been my experience with 105 series cars that there's a 1:2 ratio front and about 1:1 rear. For example, adding a half inch shim (to the spring bucket) in front lowers the car one inch. Cutting the springs kind of does the same thing except it's a little less since the spring rate increases when coils are removed.

[aeroengineerguy]

I cut a full loop out of my IAP sport springs and it lowered my gtv about 2" a little more than I would have liked, but it handles a lot better now. If I was going to do it again I would cut less off at first and keep trimming until I liked the result. Good luck

Jason

[ossodiseppia]

I'm with George on this one. Buy springs that are designed for this type of use.

[Spyros]

The car will lower more because there will be less effective spring stiffness to react the static load. If it is a progressive spring you will destroy it completely. As you can see in my profile i am an Automotive Engineer, in addition i am specialized in suspension and handling. I just want to say that the idea of lowering the car for better handling is false and in many times not required. The suspension geometry changes in a way difficult to understand. The position of the CG is the last to make a difference. What we are concerned with is the CG distance from the roll centre of the car which in some car increases as the spring shortens due to alterations in the suspension geometry. That will produce larger Jacking forces and although the car will corner better up to a limit it could roll over or slide agressively without a warning. What i want to say is that you should not listen to these "i know "mechanics or people who think that they got it all because they have open a book. Go to a proper modification centre if available and ask them if lowering the particular car is suitable for true better handling and safety. If they know their job they will first study the geometry and then give you an answer or proposal. See you!

some of the later North American cars sit higher than the factory intended simply to meet US bumper height regulations, and springs do weaken with age, getting new factory springs (what the makers intended before the DOT compromise) to correct these problems is reasonably risk free if you are staying with stock tire sizes. But Spyros is right, there are so many factors to be considered, Tire width, tire diameter, shocks, etc. the commonly held opinion is that lowering the car is an improvement, just like replacing the Spica with webers. the road and a race track are 2 different enviroments. If you do a lot of research on this you might be surprised at some of the options you have when it comes to increasing your Handling "performance" and still maintaining reasonable ride quality.