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Spring Cutting - A few Questions

929 views 11 replies 6 participants last post by  rand49er 
#1 ·
I've done my research and found out that H&R springs will be available again very soon. Before I go and drop nearly $300 on new springs, I have a few questions about cutting springs (stock, or otherwise):

1) Is there a ratio of coils cut to drop achieved (IE 1 coil = 1" drop)? If so, does this ratio change with, say, H&R springs?

2) How much does/will the stock spring rate change with cutting of coils? Or does it change at all?

3) Any idea what aftermarket springs (H&R) spring rates are?

4) Are there "perches" that our springs sit in which would lead to improper seating of the spring if you didn't cut full coil(s) off? (I've read a few people say they've cut 1 1/4 or 1 1/2 coils off, but that strikes me as a possible issue)

5) How low can you go before the spring is just too short for the suspension travel and will just pop or fall out?

6) Has anyone been part of a comparison between a moderately 'cut' (no more than a 2" drop) stock spring's ride quality, and that of a V that's on un-cut H&R's?

I think that's about all I have for now ... thanks in advance to anyone who chimes in with some useful info!!
 
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#2 ·
Well, you don't seem to be getting many answers. I'll take a shot at a few:
1. The more you cut, the lower you go. How's that? In reality, the shorter the spring gets the stiffer it gets, so it's complicated. Maybe somebody has a rule of thumb, but the real answer can only be obtained by either trial and error or with a spring formula from an engineering textbook.
2. The effective stiffness goes up. See engineering textbook above.
3. Search the forum on spring rates and you will find answers for commonly available aftermarket setups. But, if you get a setup that uses standard sizes, you can change the springs fairly economically if you decide you need more or less rate, or more or less drop.
4. I don't know what type of perch we have, i.e. if it is designed for an unground spring at both ends, one end, or what. Others can surely answer this.
5. Don't know. This is what helper springs are for. They keep a short spring in place when the suspension droops, such as when the car is jacked up.
6. Personally, I would never cut or heat-form a spring. I'd get a setup that uses standard 2.25 or 2.5 dia. units which are both stocked in various lengths and rates.
 
#8 ·
are there any other setups that utilize 2.5" springs OTHER than ground control?

I do know that MM spacers (or the equivalent) are required to lower the rear.

I'm curious why you recommend the GC kit. From what I've read there's almost a 50/50 split between people that are happy with those kits, and people who aren't. I understand that the adjustability is nice, but beyond that I'm not sure of the advantages over just lowering springs. I've read that the rear will not lower more than an inch (even with MM spacers), although the front will adjust to significantly lower than H&R or Eibach springs. All I want is a nice aggressive, moderate stance while maintaining the stock ride quality - or at least as close to it as possible.
yes. Adjustability is the only true differentiator of this "kit" from springs unless there is a performance advantage/disadvantage to using 2.5" vs stock diameter springs.

That "kit", from what I have seen, is 4 eibach springs and custom perches consisting of 3 metal pieces and a threaded cylinder. I'm thinking David Copperfield must be their marketing manager or there just aint much in that "kit".
 
#3 ·
Springs are rated in pounds (or kilograms) of force per inch (or centimeter) of deflection. If you remove 10% of the coils, you reduce the force necessary to compress the spring a given distance by 10%.

Can't recall specifically, but I believe our stock springs are in the range of 400 lbs/in. Ground Control kits offer Eibach springs with rates ranging from 500 lbs/in up to 750 lbs/in. (I have 650 rear/600 front, as an example.)

As inexpensive as springs are, I'd never modify the stockers. You also have to contend with the Nivomats self-leveling feature. If you want to lower the car, mow the neighbor's lawn, do some extra babysitting, and save your spare change then get a GC kit if you can at all do it.
 
#5 ·
If you remove 10% of the coils, you reduce the force necessary to compress the spring a given distance by 10%.
QUOTE]

This is not correct.

You don't have to take my word for it. If you want to see what happens when you cut a spring, go to the spring calculator at

http://www.engineersedge.com/spring_comp_calc_k dot htm


and click on "Open Calculator"

Then, just leave all the numbers alone except reduce the number of active coils from 10 to 9. This is what happens if you remove 10% of the coils, in rand49er's example. Then hit "Find K Constant" and watch what happens. (Answer: The rate goes up 10%, not down.)
 
#6 ·
I had cut 1 coil off my rears and half off of my fronts, no complaints here.
 
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