First I don't regard this as an argument. It's a discussion or dialogue. I don't seek to "win" anything.

OK, finally some math. Separates the marketing from the engineering. But why hold back with the simple formula that doesn't prove your point? (formula only relevant for same-length springs. That's not what we're talking about is it?

How about running an example with numbers in it?

 

Quote:

Originally Posted by ppro

…The rate of a plain old spring should not change if it's cut…

Quote:

Originally Posted by ppro

…I just don't see how the spring rate increases when the spring is cut…

It does.
Its rate increases when the number of active coils is reduced, just as a torsion bar becomes stiffer as its length is shortened.

Quote:

Originally Posted by ppro

…I am not getting any math or a practical example to support this.

http://www.afcoracing.com/tech_pages/spring.shtml#rate
http://www.swayaway.com/calculators/swayawayCalc.php#step9
http://www.pontiacracing.net/js_coil_spring_rate.htm

However, because the load height is occasionally inordinately compromised when shortening OE coil springs, the likelihood of near-fully compressing the jounce snubbers may become a more frequent occurrence. The attendant dramatic increase in wheel rate when that occurs could negatively affect the vehicle’s dynamic balance during spirited operation.

Some choose to fit springs with a higher rate that better accommodates the reduced jounce travel when reducing their ride height.
Others here have not and yet reported no deleterious results.

 

The first link (http://www.afcoracing.com/tech_pages/spring.shtml#rate) says spring rate increases as spring compresses but doesn't say what happens when a spring is cut. So it does not support the contention that cutting increases rate.

The second link ( http://www.swayaway.com/calculators/swayawayCalc.php#step9 ) appears to support the contention that rate increases as number of coils decreases.

The third link ( http://www.pontiacracing.net/js_coil_spring_rate.htm ) appears to support the contention that rate increases as number of coils decreases.

I can live with that. It's counter-intuitive but so be it.

That doesn't change what I was trying to say - and this really restated another way here:

Quote:

Originally Posted by jiii

However, because the load height is occasionally inordinately compromised when shortening OE coil springs, the likelihood of near-fully compressing the jounce snubbers may become a more frequent occurrence. The attendant dramatic increase in wheel rate when that occurs could negatively affect the vehicle’s dynamic balance during spirited operation.

But it has been reported. We have people reporting scraping the chassis on the ground. That's something I want to avoid, along with the related, and unplanned stress on the chassis.

 

you've got to be kidding me...all this because some of us want to lower our cars an inch...if my springs made in Germany are that d@mn weak, I better change them out rt now whether I cut them or not...but in reality, this little car has seen 125 many times w/ stab braking hard to reduce speed to 60-80 mph range in order to make my turn from the straightaway many, many times... I throw this car around a lot, I can't understand how cutting a spring a half coil changes anything that I will feel while doing above mentioned driving, except lower my center of gravity just a little...its more for appearance for me, but I am hoping for a little better handling, if not, doesn't matter...the original question was does it hurt anything cutting your springs...to lower your car...an inch, I don't think so, cut it in half and yes you will bottom out, distort the whole suspension, might as well add hydraulics and set her on the ground...but that's not what most have done, they have cut only a half of one coil....now, does that hurt anything...1/2 Coil...this is the answer many were looking for...I decided to do just that, others may buy a lowering kit...like eibach, but after looking into that, I don't think those springs will have the spring rate I have now...they look to be smaller in diameter...I don't have a way to measure spring rate, maybe someone on here has that answer...I want a more stiff spring if I am going to buy something else. I haven't seen a definitive answer here either way

 

The equations are both correct.

 

if you really want to lower your car do it right. If your idea of right is to just cut the springs, than sorry. You spent too much money to short cut and cut the springs. Eibach, and H&r are very good companies, to order products from. Eibach pro-kit, on my 94 t-bird, and H&R supersports on my cobra. With the h&r's I had to address many things. Tha ride quality, and stability, was awesome, on the other hand, not counting front bumper, or air dam, clearence was about a pack of clearence. This measured at the lowest structural crossmember. Then you have to think about proper alignment. I'm not sure how far the stock caster camber plates will adjust. I had to get special plates to allow for the drop. Then here was bumpsteer, and ball joints, that will get extra load on them. But all said and done, The cobra, dropped 2" up front, and 1.75 in the back, and handeled like a dream, with tokico illumina s/s. I haven't even considered dropping this car, it's kinda nice to not have to worry about speedbumps. Don't forget turtles crossing the road if they do that where you live. chris

 

the aftermarket springs, offer better ride quality, while maintaining an agressive approach into and through corners. By the time i had everything put together with the cobra, it would handle beyond where I felt safe, on back roads, and I bet it would have been awesome on a road course.