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Cutting Front Springs ... bad idea ?


ChuckinNC

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I would like to lower the front of my 1973 by about an inch. Being retired, and frugal, and trying to live off what is left of my 401-K, my first thought was to look into cutting a round off the spring. I searched the site, and found that several knowledgable folks think it is a bad idea. So, what makes it bad ? The top coil on the spring is flattened, and removing the top portion will change that. So, the top of the spring will not seat correctly. Is that the main problem ?

What springs would you recommend for purchase, and can I buy just the fronts. This modification is for a street car that gets driven sedately for the most part. I think the rear springs have sagged a bit, which makes the front end sit higher than it should, even with the metal spacer removed.

Thanks for sharing your thoughts and experience..

Chuck in NC

Chuck in NC

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ok for short term, bad idea for long term.

springs are rated and calcuated for tension, strength and weight. The moment you cut a spring it affects the load it can support. Without getting into the technical aspects and physics of it the simple answer in short is that in time your springs will weaken and flatten out.

your car will look as if it has negative camber.

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ok for short term, bad idea for long term.

springs are rated and calcuated for tension, strength and weight. The moment you cut a spring it affects the load it can support. Without getting into the technical aspects and physics of it the simple answer in short is that in time your springs will weaken and flatten out.

your car will look as if it has negative camber.

BS! cutting a spring has no effect on the metal that remains, assiming you dont heat up the metal when cutting. the metal coil that remains actually ends up STIFFER because less spring is holding up the same weight.

i did mine about seven+ years ago and LOVE IT, with Bil HDs.

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BS! cutting a spring has no effect on the metal that remains, assiming you dont heat up the metal when cutting. the metal coil that remains actually ends up STIFFER because less spring is holding up the same weight.

i did mine about seven+ years ago and LOVE IT, with Bil HDs.

Forgive my questioning, but it seems to me that cutting the springs is essentially a bad thing.

If you cut a spring, that's less overall dampering ability. Shorter, "lowering" springs have a higher spring rate, so the shorter spring could make up the height difference with more spring (dampering) force. Cutting one of the coils in a spring would produce an overall weaker spring; less dampering force than the original spring.

Now, to the effect of it's consequences on handling on a BMW 2002, you'd have to ask people that do more racing than I do.

If you ask me, go with the scienced out lowering spring, and ask Jeff Ireland to explain why if you need more convincing evidence.

ClayW
1967 1600-2 - M42 - 1521145          Follow my project at www.TX02.blogspot.com          E30 DD Project Blog

 

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Guest Anonymous

ClayW, it might be just your use of words, but your opinion that cutting a spring reduces the damping force shows either poor choice or words, or something worse.

A SPRING has essentially NO damping capability whatsoever... the shock absorbers provide dampening. You wouldn't need shocks if the spring could dampen...

That said, to reduce ride height on a car that "for the most part is driven sedately" probably isn't a good idea. The original poster is of course free to try it, but a stiffer riding car isn't likely a good thing. I am in mind of the squids with too-lowered, overly stiff Japanese cars, bouncing up and down as they drive. It looks like shit, and probably feels like it too.

I had an 02 with short, stiff springs, stiff shocks, big bars, hot motor, seats and all that. Although it was a nice looker and my little kids thought is was a hoot when I hammered it, it was NOT a comfortable ride. A 2002 in good condition is an amazing ride (for its time).

Original poster should ensure that his suspension components are in proper condition so he knows what a good 02 rides like, before he goes to messing with it.

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ClayW, it might be just your use of words, but your opinion that cutting a spring reduces the damping force shows either poor choice or words, or something worse.

A SPRING has essentially NO damping capability whatsoever... the shock absorbers provide dampening. You wouldn't need shocks if the spring could dampen...

That said, to reduce ride height on a car that "for the most part is driven sedately" probably isn't a good idea. The original poster is of course free to try it, but a stiffer riding car isn't likely a good thing. I am in mind of the squids with too-lowered, overly stiff Japanese cars, bouncing up and down as they drive. It looks like shit, and probably feels like it too.

I had an 02 with short, stiff springs, stiff shocks, big bars, hot motor, seats and all that. Although it was a nice looker and my little kids thought is was a hoot when I hammered it, it was NOT a comfortable ride. A 2002 in good condition is an amazing ride (for its time).

Original poster should ensure that his suspension components are in proper condition so he knows what a good 02 rides like, before he goes to messing with it.

Not only that (springs have no "dampering" force), but as I said before, cutting a spring results in a HIGHER spring rate. this is science, look it up. Bimmer magazine did an article a long time ago on this and they cut 1.5 coils in front and 1 coil in rear, and they ended up with about 20% stiffer springs. Hmm, guess what? Thats about the same increase as $200+ sport springs.

The problem with slammed rice cars is they are no longer riding on their springs, they are riding on their bump stops.

In any event you should ALWAYS match your spring rate to your shocks. IF you cut your springs you should at least have Bil HDs. I have about 1.75 cut off my front and 1 off the rear, with Bil HDs all around. it rides and handles WONDERFULLY. the chief benefit of aftermarket sport springs is you can get them in a progressive rate and it keeps people like jeff ireland in business.

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I dont have my chassis/suspension engineering type books at work here.. but from what I can remember. Cutting your springs increases the rate.

http://www.eatonsprings.co/atqCuttingCoilSpringsCalculations.htm

Its not a bad thing just you might want to know exactly what your'e changing when you do cut the springs..

Text from website above copied below for the lazy ;)

--------

Taken from eatonsprings.com

Tech Question - Cutting Coil Springs, with calculations

Q - Mike,

Finally, I can ask an expert …. I'm a member of a Classic Mustang forum where the "popular wisdom" is that if one cuts a spring, say a fraction of a coil (like 1/4 to 1/2), the spring *rate* increases …. I'm an engineer (but alas an EE!) with no practical knowledge on the matter -- BUT, this "popular wisdom" tends to run contrary to my intuition …. OK, within elastic limits of a spring in compression, does cutting a spring's free length change the rate (i.e., the "k" in F=k*x)?? …. I think it changes the rated load (as a percentage of the reduction in overall length) as the reduced overall length also reduced the total "F," or load, the spring can handle (max deflection/compression … but I just don't see how the metal knows that part of it has been lopped-off or not …. so, is *k* a function of spring length (and number of coils) …. I would really appreciate a bit more of information on what factors drive the *k* value for a given spring design (mostly I'm focused on coils for front springs here) …. I've read your web sites Spring Tech 101 and it doesn't address this specific question in detail …. also, I know lots of restomod folks cut springs to achieve a certain ride height ….. but is this really the best practice if limited to less than, say, 10% of a spring's original length?? …. I think I already know the answer to this, but I want an expert opinion please ….

and, do you by chance know what the factory ride height of a '67 Mustang GT at front and rear as measured from the spindle/axle centers to the fender lip center are?? …. I cannot find this data anywhere …. Scott

A - Scott,

"Popular wisdom" rules. Cutting coils does increase the spring rate. Let me explain why.

The strength of a spring, leaf or coil is a function of the cube of the steel used. Keeping with the subject of your question, coil springs, the diameter of the wire and the length of the wire will give us the amount of steel used.

For this whole discussion we will be talking about springs with the same wire diameter and the same inside diameter. The only thing that will change will be the length of the wire used to wind the spring.

The longer the wire is the lower the spring rate. As the wire get shorter, such as when cutting the coil, the spring rate increases.

So everyone has a clear understanding lets describe what "rate" is. Rate is the amount of weight it takes to deflect a spring one-inch.

A very common mistake is to think that spring rate is how much a spring supports. How much weight a spring is designed to support is called "Load" or "Designed Load" or "Load Rate". This is cover in Spring Tech 101.

Rate and Load Rate are two totally different animals.

The calculation to find the rate of a coil spring is:

11,250,000 times the wire diameter to the 4th power divided by 8 times the active number of turns times the mean diameter cubed.

Active turns are the number of turns of the spring that do not touch anything. Any part of the coil which makes contact with anything becomes inactive, that is it no longer functions as part of the spring.

The mean diameter is the inside coil diameter plus one wire thickness. Or the outside coil diameter less one wire thickness.

Let's say for example a 1967 Mustang GT front spring is made from .610 wire and has an inside diameter of 3.875" and has a free height of 16.145" (not installed) and is deflected down to 10.5" (load height) when loaded to 1,519 lbs. (load rate) This spring has a spring rate of 269lbs.

This spring has 9.33 total coils but 1.33 coils touch the spring seat so they are inactive leaving 8 active turns. (I know this from the Ford blue print).

The mean diameter is 3.875 + .610 (The inside is the important diameter because it is the inside of the spring which is used to locate the spring on the corresponding suspension parts. The outside diameter is not considered because it will change with a change of wire diameter)

Do the math -

11,250,000 x (.610 x .610 x .610 x .610) / 8 x 8 active turns x (4.485 x 4.485 x 4.485) = 269 lbs.

Double check the math - 16.145 - 10.5 = 5.645 deflection. 1,519/5.645 = 269

Now if we cut say 1/2 turn off this spring the active turns become 7.5.

So 11,250,000 x (.610 x .610 x .610 x .610) / 8 x 7.5 x (4.485 x 4.485 x 4.485) = 287 lbs

While the rate is increased the load is unchanged. Rate is the amount of weight required to deflect the spring one-inch while load is the amount of weight the spring will support at a given height.

Cutting coils is limited to those types which have tangential ends. Tangential ends are those which spiral off into space. If you tried to stand the spring on end it would fall over.

Square ends and pigtail ends, both will stand up, and can not be cut because the finished product will not mount correctly in the suspension.

See this tech question on Cutting Coil Springs for a more complete explanation.

When altering ride height one must be aware of much more than just the springs. Brake lines, steering, shock length and other areas of interference. We do not offer coil springs which will alter any ride height more than 2-inches. Nor do we recommend anyone alter the ride height more than 2-inches.

While we have all sorts of springs which will vary ride height, spring rates and ride quality on the shelf, cutting coils may be, in some cases, the only way to achieve the desired stance one is looking for.

I do not know the distance from the spindle to the fender lip, but we do have other measurements which may help. Send me your fax number.

I hope this answers your question and enjoy your t-shirt. - Mike

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One more thing...

I thought I better define Spring rate:

Spring Rate is the amount of weight needed to compress a spring a certain . Springs are rated in LB/in (in metric system kg/mm), or specifically, how many pounds of weight are required to depress the spring by one inch.

Taken from http://www.tuninglinx.com/html/spring-rate.html

Again the stuff i nabbed from the sites seems right, but i'll hit the books this evening to confirm.

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With so many 2002s equipped with lowering springs, one should be able to locate a good set of stock springs for next to $nothing. Then you can experiment.

I cut coils on an'02 once. It works okay until you load the trunk up with stuff like a large load of groceries plus a couple passengers, then the rear suspension tends to bottom easily. Trim the coils with moderation, no more than the 1 or so coils as suggested.

If all you want to do is level the car, perhaps inspecting the spring perches and replacing the rear rubber spacers is all you need to do.

Jerry

no bimmer, for now

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