What, exactly, is the argument against cutting springs?

thehackmechanic

thehackmechanic

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My 3.0 is showing more of a gap above the tops of the tires than I'd prefer. What, exactly, is the argument against cutting a coil off the springs? 2002 folks do it all the time. I read that the issue is that the spring won't sit as neatly square in the perch, but, again, how is this different from cutting springs on a 2002? This is a sedately-driven car; I'm not going to be catching air time in it. It currently has KYBs in it, though I'm thinking of ponying up for Bilstein HDs. I have an old set of springs from a parts car that I can cut. I am aware of the issue of lowering possibly causing rubbing problems with the staggered Alpinas, but that issue persists whether I use new lowering springs or cut a coil off existing ones.
 
the spring rate goes up with cut springs, for one.
we used to cut springs when we were teens and didn't have the money for
springs in the right height and spring rate.

springs have a flattened top and bottom. if you cut it, the end will have an abrupt end.
and won't sit flat.
 
Most modern car springs are not linear, they are progressive. That means you will be eliminating the most compressable (if you cut from the top) or the least compressable (if you cut from the bottom) parts of the spring. The spring rate varies along the spring to provide the best spectrum of suspension absorption, when coupled with the dampers. If you cut from the top, the springs become much harder, and have little travel. However, they will not absorb small bumps, making the car feel much rougher. If you cut the bottom, the springs will be overall much softer, causing the vehicle to bottom out easily.

As noted, they are also box-end springs, which means the end is crafted such that the last coil forms a flat surface, granting even force distribution around the radius of the spring. Without the box end, the spring, when compressed, will "bow", rather than compress straight down. This will also compromise the resultant spring rate, as you are only compressing a part of the spring at that point, while the other side is actually stretched.

An alternate old-school trick to "get low" is to heat the coils selectively. Heating a coil enough will cause it to lose its "springiness", leaving the box in place but still lowering the car. The downside is the shortening of the fatigue life of the spring, so you could be driving along and the spring will crack.
 
Yea, but an e9 doesn't have progressive springs, so cutting out a fraction of a coil seems like a valid way to lower the car. And, if you cut from the end that has been flattened, a little time on the grinder will duplicate the original profile on the newly cut end.

In my opinion, cutting a spring is a much better procedure than trying to de-temper it with heat. It would be difficult to get an even de-tempering throughout a single spring, AND it would be difficult to get an equal de-tempering between a pair of springs.

If you do cut X" off your spring note that a little algebra is needed to determine the amount of lowering that will result. For a given force (e.g., the weight of one corner of a car) a spring will compress by the same %, even after it has been shortened (*). So, if you measure your spring's compressed length as 12", and its uncompressed length as 15", then it is compressing by 1 - 12/15 = 20%. If you cut 1" off of it, it will still compress by 20% under the same load, so its new compressed length will be (15" - 1") x (1 - 20%) = 11.2". So in this example (where I just made up the numbers) cutting 1" off the spring while it is sitting on the garage floor would reduce its compressed length by .8".

On an e9, the amount the compressed spring is shortened equals the amount the car is lowered, since the bottom of the strut acts directly on the lower ball joint. On cars with spring pans, some additional calculations are required.

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* For extra credit, what happens to the rate after a spring has been shortened? In the above example we are reducing the spring's length to 14" / 15" = 93.3%. Its rate will increase to 1 / .933 = 1.071 of its original rate. In other words, it will be 7.1% stiffer as measured in lbs force / inches compression.
 
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I cut my springs a while ago, the car looks better and I have not noticed any change in the ride
 
With your alias you have to go with cut springs, don't you? I cut 1 coil off all 4 springs on my first coupe years ago- perfect height (some might say too low), firmer but not harsh and a little extra camber. I used a dremel and then angled the cut and smoothed it out so it wouldn't cut up the pad. If your going to lower it you'll probably never go back to stock height anyway so why not try it first?
 
cutting springs?

<< With your alias you have to go with cut springs, don't you?>>

:^)

Thanks guys; valuable information all. I don't see the downside of, ahem, hacking up a set of springs that's been sitting under the porch at my mother's house for 20 years and seeing how it turns out.

--Rob
 
I was thinking about cutting my springs, but decided to go with the lowering springs from La Jolla for the piece of mind. I installed them yesterday. It took less than 2 hours, and the car looks and handles great. $400 is steep, but includes shipping.
 
there ae so many lowered springs out

eibach makes almost any spring rate. size, radius
i designed my custom e31 suspension that way.
most parts were from e46 ground control.
once you know the desired spring rate and dimensions. finding what fits your needs will be the easy part...and my lowered springs cost 140 for two front
 
I've cut 1.25 or 1.5 coils off the rear and it's worked well.

In the front, I cut a coil without reprofiling the top and the spring slipped off the perch while I was driving...so, some time with a torch to profile the ends and he car was lower but still not "there."

I ended up getting a coilover kit from ground control along with camber plates. I'm using the stock perches, so no welding. Ride is good and it's almost as low as I'd like.

I think my front camber is around 1.5 degrees negative, I had the same concern about the fender lips so I rolled them. FWIW my car was unusually high in the front, and the spacers had already been removed.

coupe%20002.jpg
 
Lowering springs

I just bought a set from Carl N. for $349 front and rear...nice. Get 'em while they are hot!
I believe he has done the math...
 
I agree, I have them as well. The front is lower than the rear and the rear is a little too high for my taste, will cut the rear springs to match the front.
 
Found the springs from the 2800cs that I parted out in 1987. Cut one coil off both the front and the rears and installed them yesterday. Started raining so I haven't taken the car out to check the stance yet.
 
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