Coil Spring Debate

[fuse]

I need to put a spreadsheet together and compare. It's hard to do this riding in a truck stuck in traffic. The guy driving is no help either...

I have something for you. Try this out: https://www.thespringstore.com/spring-rate-calculator.html

Doubling the spring length does indeed halve the spring rate, but only if you double the number of active coils at the same time. You can look at the math or try out some different values in the calculator to verify this.

 

[JMT]

But stacking them DOES change the rate of the ASSEMBLY of the 2 springs.

By ASSEMBLY are you saying that once you have cut a coil it is shorter and by doing so you have directly changed the RATE? Just trying to get clarification on your conception of rate and coil length

 

[Fargo]

So, why does a 933 spring have a lower rate the a 934?

Because the 933 has fewer turns than the 934. (I have a spreadsheet full of this stuff)

OME # number of turns

OME933 11.2
OME934 10

These coils use the same 14mm diameter bar

Post was edited to remove 949 info

 

[bobthetj03]

This is getting above my pay grade.

 

[Fargo]

By ASSEMBLY are you saying that once you have cut a coil it is shorter and by doing so you have directly changed the RATE? Just trying to get clarification on your conception of rate and coil length

By assembly I simply meant stacking them on top of each other. The rate of the spring will not change by cutting it. It can't, the rate is the same through out the spring by definition of a linear rate.

But stacking springs will give a different rate as indicated in the formula provided earlier.

 

[bobthetj03]

Because the 933 has fewer turns than the 934. (I have a spreadsheet full of this stuff)

OME # number of turns

OME933 11.2
OME934 10
OME949 7.1


The 949 also uses a thicker bar diameter

On my phone and didn't have arb spec sheet. I thought the wire diameters were the same.

 

[Fargo]

MODERATOR, CAN WE GET THIS MOVED TO A NEW THREAD?

This is a great discussion but we are really off topic.

 

[Fargo]

On my phone and didn't have arb spec sheet. I thought the wire diameters were the same.

Only the LJ 949 had a different diameter. The other two were the same. I should not have kept it in the list. I'll edit the post.

 

[fuse]

The rate of the spring will not change by cutting it.

I think you might want to check your math.

 

[bobthetj03]

MODERATOR, CAN WE GET THIS MOVED TO A NEW THREAD?

This is a great discussion but we are really off topic.

It's my thread, so I'm ok with this turn. We've pretty much come to a conclusion with the original topic. Maybe add to the title.

 

[JMT]

But stacking springs will give a different rate as indicated in the formula provided earlier.

That's what I have trouble seeing.

Because the 933 has fewer turns than the 934. (I have a spreadsheet full of this stuff)

OME # number of turns

OME933 11.2
OME934 10
OME949 7.1


The 949 also uses a thicker bar diameter

Yes, the less number of turns the farther the coils are spaced apart and the spring rate will be higher.My conclusion on why the OME HD 2" kit paired the 933 and 942 was to keep the factory rake, or something close to it. But nobody on here wants to keep the factory rake, they want level, so 934 and 942 paired should eliminate that. Thoughts?

 

[Fargo]

I have something for you. Try this out: https://www.thespringstore.com/spring-rate-calculator.html

Doubling the spring length does indeed halve the spring rate, but only if you double the number of active coils at the same time. You can look at the math or try out some different values in the calculator to verify this.

Nice find. I'll have to play with this.

You guys are so fast to respond I think I am missing half the messages.

Sorry, but I'll have to take a break from our discussion. I need to get some work done. But I'll come back later.

I think I'll have to go back and re read everything in case I missed something too.

 

[Damazzaro]

K will double if L is halved. Assuming a basic and symmetric spring setup.

 

[JMT]

Can someone who has a pretty good grasp of this, like @Fargo, or possibly someone else, put some working principles together (after you get some work done, of course)? For starters, something like

Principle 1: linear spring rates are equal throughout the length of the spring
Principle 2: a shorter spring will have a higher spring rate (all else being equal)
Principle 3:

 

[Fargo]

K will double if L is halved. Assuming a basic and symmetric spring setup.

Depending on how you do it. Cutting the length in half with a saw or torch will not change the rate because the amount of material is also changed. But if you design a new spring with the same amount of material then the rate will change.

We have to always keep in mind the length of the bar the coil is made with. Its just a lever in the shape of a coil.

I gotta go. You guys are great. I love the discussion and the thought. But I gotta earn a living. I'll be back.

 

[JMT]

On my phone and didn't have arb spec sheet. I thought the wire diameters were the same.

They are for 933 and 934, they're both 14mm, but he brought in 949, which is 17mm. Don't know why he brought that into the discussion, but I think we're alll looking at the same sheet

 

[Fargo]

..Don't know why he brought that into the discussion, but I think we're alll looking at the same sheet

That was my mistake. I removed it. Sorry for the confusion. The 933 and 934 are both 14mm. From the arb/ome spec sheet you guys are likely looking at.

 

[Damazzaro]

Depending on how you do it. Cutting the length in half with a saw or torch will not change the rate because the amount of material is also changed. But if you design a new spring with the same amount of material then the rate will change.

We have to always keep in mind the length of the bar the coil is made with. Its just a lever in the shape of a coil.

I gotta go. You guys are great. I love the discussion and the thought. But I gotta earn a living. I'll be back.

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.

 

[JMT]

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.

This makes sense because if you envision your coil spring as a straight bar of steel, at full length you are able to use less force to get the same leverage as you would if you cut that steel bar in half. So, cutting the coil decreases the amount of work it can do by a factor I'm sure is discovered using a physics formula.

 

[fuse]

Here's the formula from the page I mentioned earlier.

D = D outer - d
G = E ÷ 2 ( 1 + V)
k = Gd^4 ÷ (8D^3 na)

Where:

• d = Wire Diameter
• D outer = Outer Diameter
• D = Mean Diameter
• E = Young's Modulus of Material
• G = Shear Modulus of Material
• L free = Free Length
• k = Spring Rate (Spring Constant)
• na = Active Coils
• V = Poisson's Ratio of Material

That's a lot to bite off, but if you're comparing springs made of the same material, E, G and V stay the same. If they have the same outer diameter and wire diameter (as might be the case when comparing two TJ springs from the same manufacturer), then D and d stay the same.

Something to note: L is not a factor in the calculation. That is, if everything else stays the same including the number of active coils, two springs of different lengths have the same spring rate.

Based on this calculation, what happens if you double the number of active coils? Or halve the number of active coils?