My Tech Week contribution-Cutting coils

I have no expectations of winning a damn thing but I continually see threads about how to or how much to cut coils.
I see lots of responses like
"cut 1 rung and it'll be perfect" Really? Will it? Maybe but more than likely the poster got lucky and you will not.
or
"cut a bit at a time 'til it sits where you want"
Yep, that'll work but it's a pain in the ass and while I don't consider myself lazy I'd rather not pull the front end apart 2, 3, 6 times to get it right.
Here's my method and some pics of mostly OT cars I've done this on in recent history.

A little simple math can be your friend. In most cases most double a arm front ends have the coils about half way between the pivot point and the wheel giving you a 2:1 ratio on what you cut from the spring. What that means is that whatever linear height you remove from the spring will be double at the wheel. So if you cut 1" of spring (from the non flat portion) the car will drop 2". I've done my last 4 cars (64 LeSabre, 66 Catalina, 67 Riviera, and 62 Montery) the same way and it's been spot on first time every time.



What to do out back? If the spring is directly on the axle out back then the ratio is 1:1 so 1" of spring will drop it 1"
Good luck and have fun!



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Makes sense. When we pulled my old truck apart, we had one loop in one coil already broke so we just matched the other side and got the desired effect without guessing. Like you said, just lucky.

 

Good tip Mike! When I get around to fixing up my wife's Rambler, I'll be using this tip.

 

emmm. well it's not quite linear because as you cut more spring off you continually raise the spring rate so it has less and less effect.

OC

 

You are absolutely right but I omitted mentioning it because from my experience the rising rate of the cut spring is relatively minimal and has little effect.

 

More math for ya -

In the right hand pic, to get exactly a 1" rise on the lower control arm, the spring needs to be cut by 1 divided by the cosine of the angle of the spring from vertical.

 

Yep, and unless you have another car you drive to compare it to, you'll never feel it.

 

Thanks for the post.Nice cars.Hard to argue with results.

 

This is interesting.The front is easy to figure out but on the rear if your car has the spring located on the lower control arm how does this work?On a 59 Chevy this is how the rear spring is mounted.

Also on the 59 the spring will only sit one way on upper and lower pots.So you would have to remove one coil to have it so the spring will sit right.

 

Helpful...I was thinking of going a bit lower with my front end and this thread couldn't have been timed any better.

 

Well the same math applies but like you mention the spring mounting style will dictate what you can do. I'd do the back first then that will tell you how much to do the front to get the desired stance.

 

So on the rear do you measure from the center line of the rear axle to the center of the spring?

 

You would measure from the centerline of the front control arm pivot to the centerline of the rear axle. We'll call this A.
You would then measure from the centerline of the front control arm pivot to the centerline of the spring. We'll call this B
You then divide the first measurement by the second measurement to get the drop ratio.
Here's a couple of examples with some nice simple measurements:
-If A=3' and B=1.5' (so the spring is half way between the front pivot and the axle center line) you would get 3/1.5=2. So cut 1" of spring and get 2" of drop.
-If the spring were further forward..say 1' from the front pivot the numbers would now be A=3' and B=1' you would get 3/1=3. So cut 1" of spring and get 3" of drop.

So for your deal where you have to cut 1 full coil at a time you won't be able to control the amount of drop but you will be able to figure out approx. how much drop you'll get from each coil.

I'll post up a pic of the rear scenario when I get to a computer with a decent graphics program. I can't handle trying to do stuff in MS Paint.

Hope this helps.

 

This can also be applied if youre swapping coils for bags, to calculate inflated heights
and deflated height by comparing the coil lenght when the coil is still in place w/out having to go mad mocking all up.
This way you'll know already in what position you want your bags mounted to achieve maximum and minimum desired heights.
Hope i made sense!
Anyway, thanx Mike.

 

Good info on this post...thank you!