The Official Spring Rate Calculator Thread Part II

[muddermilitia]

And here are your results:

52" Springs

1. SAE HS-788 - 286lb/in (SF = 1.15)
2. Chassis Engineering - 279lb/in
3. Ranger Station w/ taper - 265lb/in
4. Excel from Pirate - 235lb/in

64" Springs

1. SAE HS-788 - 186lb/in (SF = 1.15)
2. Chassis Engineering - 152lb/in
3. Ranger Station w/ taper - 138lb/in
4. Excel from Pirate - 141lb/in

How is that for service?

BTW, I am using the active length of the springs in all calculations (including the Ranger Station calculator). The exception is the calculators from Pirate where they clearly are using the entire length in the equations.

Wow, I knew the rears were softer than the fronts but not by that much!

damn, thats a big difference from the 52s to the 64s, i guess thats a nice flexy truck.

Yea, I guess once my engine hoist is all fixed I will have to flex out the truck and see how it does.

 

[BGKYK5]

Triaged, yes I am using the equation from the spreadsheet you posted on Pirate. Where did you dig it up? Thanks for the link, I'll have to spend some time digesting all that!

 

[Triaged]

Where did you dig it up? Thanks for the link, I'll have to spend some time digesting all that!

The spreadsheet I tossed together a long time ago. I think there might even be a thread on here about it. I can't remember where the equations came from.

I'm going to have to pick up one of those old Chevy Power Manuals on ebay sometime. MJ said it was an older version of this
http://www.sdparts.com/product/24502488/ChevroletPowerManual.aspx
Lots of engine info and just the last chapter was on vehicle dynamics.

 

[BGKYK5]

Thanks. I have a fair collection of books on vehicle dynamics and stuff, but I am always on the lookout for more info.

 

[BGKYK5]

Well I finally went through and did the math with the Chevy Power equations posted by Traiged. The result? The equation reduces down to the same as the Chassis Engineering equation in the case of symmetric springs. We'll need somebody to post up the measurements of a 56" or other non-symmetric spring to see what it does.

Here is the equation:

R = (WN/192)*(1000T1/(L-L'))^3*((b/a + 1)^4)/(b/a)^2

The variables are the same as in the original post (I just added [a] and to that post).

For non-symmetric springs (like 56" springs) I'll also need:
a = the length of the spring ahead of the axle (about 30" for a 56" spring)
b = the length of the spring behind the axle (about 26" for a 56" spring)

 

[BGKYK5]

I picked up some 56" springs (thanks JohnnyChimpo!) and finally got around to measuring them. IIRC, they are from a late 80's 3/4T 'Burb.

Here are my results:


L = 56"
L' = 4.2"
N = 4
N' = 1
W = 2.5"
T1 = 0.360"
T2 = 0.345"
T3 = 0.345"
T4 = 0.345"
a = 30"
b = 26"

1. SAE HSS-788 - 261lb/in
2. Chassis Engineering - 280lb/in
3. Ranger Station w/o taper - 280lb/in
4. Excel from Pirate - 239lb/in
5. Chevy Power - 245lb/in

So according to Chevy Power, an offset center pin slightly reduces the spring rate. It is also interesting to note that these results are slightly stiffer than my 52" springs. However, the longer length should make the spring rate more linear (the rate shouldn't increase with travel as much).

 

[72k5mike]

What if I want to know how much my rate changes by using an add a leaf?

I have a full length leaf that was taken from a tuff country pack and added to my 7 leaf waggy front springs. The spring is 0.25" thick (I would have to actually measure it, that is a guess), 47" long, 2.5" wide.

Would I just use the formulas given and input the leaf number count as 1?

 

[BGKYK5]

I would calculate the rate with the original pack, then calculate the rate for the pack with the additional leaf (depending on the equation you may just have to change N from 7 to 8).

 

[Duntz00]

I've got some 70's dodge 52's with offset center pin I plan to swap into the front of my truck I'll get some measurements off of for ya.

 

[Blue85]

I also measured my stock '89 front springs and the 4" lift Trail Master (AFAIK) front springs on my '91. This is what I got:

Stock Front

L = 47.25"
L' = 3.66"
N = 2
N' = 2
W = 2.9"
T1 = 0.400"
T2 = 0.400"

Which resulted in:

1. SAE HS-788 - 399lb/in (SF = 1.20)
2. Chassis Engineering - 373lb/in
3. Ranger Station w/o taper - 373lb/in
4. Excel from Pirate - 422lb/in

So the stock front springs are stiffer than 52" rears and the published rate for EZ-rides? Is this the stock 4-leaf pack? Have you crunched the nubmers for EZ-rides based on measurements?

 

[BGKYK5]

The stock fronts are definately stiffer than 52's. If you have dimensions on EZ-rides I'll crunch the numbers.