Okay im a high school kid and i wasnt smart enough to take physics so i need help. Me and my friend are arguing about cutting springs and while there is a miriad of problems associated with it but the one we were talking about is the infamous "it will make your car bounce around" and hes saying that if you simply put in stiffer shocks/struts it would work fine but im not convinced. This the best thing my friend could put forward as to why the bouncing around wont happen is this (we were comparing 2 springs, both have the same spring rate but one is half the size (an exageration of real life) so basically the cut spring and the other is a full size spring)

see u can't do that tho b/c comparin that on will have , the taller one has already started compression
a bump applies the same amount of compresstion no matter the height, the taller one would compres from 0-25% from its uncompressed state of 100%
now if u cut it, of that 100% lets say u take off 25%
so u start at -25% BUT the 25% doesn't exist b/c its what i have cut off SO the the range in which the spring compresses is 25-50%
but both r 25% still

so can someone explain why cut springs make your car bounce around??

 

The thing that comes to mind first off, is there's less travel between top height and bottoming out... so if it hits bottom faster, it's also going to come back up faster... less shock/strut travel to do dampening...

I also might suggest you actually use whole words and complete sentences so those of us that don't know your shorthand can under stand it. And actually verbalize what you are trying to say.

 

Cutting a spring increases the spring rate.

 

Yes. It increases it dramitically and they do not perform like they should. They can become oscilatory and thats why you get the bad bounce. Also, no strut or spring will be able to dampen a cut spring like that effectively.

 

A spring cut in half might as well be a solid rod! :-)

 

I cut a 1/2 coil off and reflatted the ends on my rear coils after new Konis boosted me up and it rides the same as before. If you're cutting 1 or 2 coils I'm sure it would be different. But if you're doing suspension work, you probably want to get a set of good struts/shocks anyway.

 

Cutting 1 coil from your spring adds roughly 10% to the spring rate.

 

The bouncing you are referring to is related to worn shocks and/or struts. Bouncing being related to the springs is a myth. Cutting springs increases spring rate, and creates more oscillation. More spring rate on worn shocks/struts means more bounce. Never cut more than one coil - EVER! Even cheapie shocks/struts have no problem controlling very stiff springs.

Excessive bounce is ALWAYS a shock/strut problem and NEVER a spring problem.

Example:

I cut my front and rear springs 3/4 coil. I have the ORIGINAL 1985 struts up front with some unknown 8 year old shocks in the rear. I get no bounce. I've ridden in several other thirdgens with aftermarket springs/shocks/struts. Mine rides nearly identical.