Coil Spring Debate

[Fargo]

K should change because it inversely related to the length of a spring. So cutting a uniform spring in half with yield a doubled k value

Edit:
If you cut the spring in half you now are moving the spring half the distance of the original size so it will require 2x the same force. Where k is equal to force over delta length.

I'll have to look into what you are saying closer. We are missing something in our communications here. I think it has to do with the free length of the spring after it is cut. Again coming back to the amount of material and bar length. Because I am pretty sure I can't just go cut my LJ coil and magically have a stiffer spring to carry a load better. So I maintain that cutting in half will not change the rate. Only the free standing length gets shorter. Cutting the amount of material in half is a different story.

EDIT: Which I guess we are doing as well if we cut the spring in half. The question that remains then is free height. (Assuming all else is equal)

I'm going on pause now. I'll have to re-read and think through everything. I don't know this stuff as much as I am just able to think through it, but that takes time if I haven't considered it before.

 

[bobthetj03]

@Chris, could you move posts to here from post#221 on from the control arm bushing/nvh thread. I think this deserves its own thread after all.

 

[Chris]

@Chris, could you move posts to here from post#221 on from the control arm bushing/nvh thread. I think this deserves its own thread after all.

Done!

 

[jjvw]

https://www.eatondetroitspring.com/cutting-coil-springs-calculations/

This site explains that a spring will increase in rate as the coil is cut. A spring's rate is determined by the number of winds (along with the wire diameter). Cutting the winds from a coil (shortening) will increase it's rate because it now takes more force to compress fewer winds.

 

[Fargo]

K should change because it inversely related to the length of a spring. So cutting a uniform spring in half with yield a doubled k value

Edit:
If you cut the spring in half you now are moving the spring half the distance of the original size so it will require 2x the same force. Where k is equal to force over delta length.

I've been thinking about this along with my reply earlier in my edit where I said that we are in fact cutting the material in half when we cut a spring in half. Once I wrote that comment, I realized what I just said. It then started to make more sense that the spring rate might infact double when you cut the spring in half. Because we now have a shorter lever. So what I had said before about rate not changing may not have been right.

So know I have to go back and re-evelauate if it would make a difference if the springs are connected or not. I'm inclined to think now that jjvw was correct and that it does not matter if they are one 10" spring or two 5" springs. It is the rate that matters. In which case, the dual rate single coil would act the same as a stacked assembly of 2 coils. So, I guess I'll be rewinding some of my thoughts now and doing some reading on the web pages provided. Thanks guys, this has been a great discussion.

 

[jjvw]

This is fun stuff to figure out. I think I have a slightly better grasp of combined rates now.

 

[Grandpastyx]

I think it makes sense or makes it easier to visualize if we think of a 24 inch breaker bar it will undo a wheel nut with half the force of a 12 inch one but then if we cut the 24 inch into two it will now act like the 12 inch and so take twice the force to undo the wheel nut then if we weld it up again it just becomes a 24 inch bar
The same with springs the longer the bar is that makes up springs the more leverage and so softer the spring
And with the number of coils that makes up the spring in order to fit in the same space or same spring height a softer spring will require more coils spaced closer together and a harder spring of the same height will have less coils at a steeper angle because the bar that is used to make up the spring is only half as long but still has to end up at the same height I hope this makes as much sense as it did in my head

 

[Fargo]

I think it makes sense or makes it easier to visualize if we think of a 24 inch breaker bar it will undo a wheel nut with half the force of a 12 inch one but then if we cut the 24 inch into two it will now act like the 12 inch and so take twice the force to undo the wheel nut then if we weld it up again it just becomes a 24 inch bar
The same with springs the longer the bar is that makes up springs the more leverage and so softer the spring
And with the number of coils that makes up the spring in order to fit in the same space or same spring height a softer spring will require more coils spaced closer together and a harder spring of the same height will have less coils at a steeper angle because the bar that is used to make up the spring is only half as long but still has to end up at the same height I hope this makes as much sense as it did in my head

That makes sense to me. I think I messed up in some of my initial thoughts, because I wasn't thinking about how cutting the spring in half also cut the leverage force in half. I think this is a good explanation on that point.

 

[Fargo]

Some interesting reading about linear vs progressive coils on the page linked below. They also have a nice calculator and other info.
https://www.hypercoils.com/tech-tips/linear-vs-progressive-rate-suspension-springs/

I think we have some links to some pretty good info in this thread for anyone who wants to know more about springs.

 

[bobthetj03]

Nice article! This leaves me with a couple of thoughts. Since a dual rate spring provides better roll control, maybe that would be a better choice of spring for those that run an AR? Secondly, would a dual rate spring for say a 3" lift not provide enough free length for the transition rate to be of any use? I'm thinking anything less than a 4" lift spring in a dual rate may not play well with our jeeps.

 

[JMT]

One of the things about most of the articles I'm sure we've all read, is they are racing oriented. I wish there was more info out there directly related to our form of off-roading or even daily driving.

According to the article, linear rate springs contribute nothing to roll control, since the inside spring is offsetting what the outside spring is accomplishing, resulting in zero additional control. This is different than I've read elsewhere, but it does make sense. Second, how long of a spring is the relatively long spring referred to in the article, such that dual rate will be of any use for us? We're not taking corners at high speed, but we do come off of rocks and cause sudden rocking of the Jeep back and forth at times. We also load down our Jeeps with gear at times. These would have an effect on whether those upper coils would remain active and be any help with roll control. There are lots of variables here.

 

[Fargo]

Nice article! This leaves me with a couple of thoughts. Since a dual rate spring provides better roll control, maybe that would be a better choice of spring for those that run an AR? Secondly, would a dual rate spring for say a 3" lift not provide enough free length for the transition rate to be of any use? I'm thinking anything less than a 4" lift spring in a dual rate may not play well with our jeeps.

Antirock or not, it would provide more front end stability once you get into the firm rate.

One of the things about most of the articles I'm sure we've all read, is they are racing oriented. I wish there was more info out there directly related to our form of off-roading or even daily driving.

According to the article, linear rate springs contribute nothing to roll control, since the inside spring is offsetting what the outside spring is accomplishing, resulting in zero additional control. This is different than I've read elsewhere, but it does make sense. Second, how long of a spring is the relatively long spring referred to in the article, such that dual rate will be of any use for us? We're not taking corners at high speed, but we do come off of rocks and cause sudden rocking of the Jeep back and forth at times. We also load down our Jeeps with gear at times. These would have an effect on whether those upper coils would remain active and be any help with roll control. There are lots of variables here.

Yeah, most of what I have seen is in regards to racing. But I think our suspensions which have 8" - 12" +/- of travel is a lot more travel than they are working with. So there should be plenty of room for a progressive coil to work with, even with only a 2" lift. I think the bigger challenge is the difference in weight between a stock Tj with a soft top and a 4cyl versus and LJ with a hardtop, 6cyl and heavy armor.

 

[bobthetj03]

That's why I'd like to see more choices in spring rates with the dual rate springs. Say a TJ with a winch, hard top, 6cyl. can run a 150/190lb in. spring, vs a lighter TJ, 4cyl, soft top, a 130/160 lb in. spring. You get the jist.