anyone got the number off the top of their head?

Need to do some tuning on the Wolf, thinking of XJ or ZJ coils.

The numbers would really help

Cheers

Bill

Bill...

Here's some misc. ramblings I cut 'n pasted from Naxja a while back when the topic of spring rates popped up...

OEM is supposedly 147 lb/in rate.
Tera 4" TJ coils give 4.5" of lift on an XJ and have a 200 lb/in rate , 20.25" tall unloaded
Tera 3" TJ coils give 3.5" of lift on an XJ and have a 170 lb/in rate
Rusty's 4.5" coils give 5" of lift and have a 150 lb/in rate, 22" tall unloaded
RE's 4.5" ZJ coils give 6"-6.25" of lift on an XJ and have a 200 lb/in rate, 22" tall unloaded
Rustys 3" coils give 3" and have 150 lb/in rate.
Rancho 3" coils, at least the old coils give about 2 1/4" of lift on an XJ and have a very high 235 lb/in rate.
OME coils give 2.25" - 2.5" of lift and have a 148 lb/in rate

I agree with most of the posted numbers but after discussing rates with Rustin and Ryan at RE:

RE ZJ coils are 240 lb/in.

The old Rancho's (which have a great rate for a long arm design) are aroud 260 lb/in.

Rustin said he might have a set of coils made for us to test in the desert that will run in the 260 range. but provide about 6-7 inches of lift. Yummy.

Andy

Thanks for the info guys,

Do you know what the stock ZJ v8 rate is?

Do you know if the diameter of the ZJ coils is different from the XJ.

See - what I'm after, is some new coils for the front of the Wolf that are a little taller, and a little smaller in diameter than the present coils (69 El Camino if ya can believe that!). Not because I want any "lift" at all - but I need to lift it a bit to gain some room for more suspension / steering linkage options. Got a bad axle wrap problem and a bad habit of smashing steering linkages to bits.

The current coils are 6-3/4" diameter :eek: and 12" loaded (and awfully soft too)

An old Xj set I have are about 17-1/2" free and 5-1/4" diameter.

Bill...

ZJ coils and XJ coils are the size diameter. As a reference, XJ Up Country Coils are the same as ZJ std coils. The only difference is the diameter of the coil wire (1/2" vs 5/8"). If you ever need to figure spring rate for "mystery" coils or leaves, do some calcs as indicated below. If you can't read this, just copy and englarge.

http://www.imagestation.com/picture/sraid19/pbf31e61bc1716baf1c2de51e79529b1d/fdc2a247.jpg

GonPostal,

If i read that right, it's

[11,250,000 x coil spring wire diameter^4] / [8 x # of active coils x avg. coil diameter^3]

Izat right?

Great info

Yep... that be it....

GonPostal,

What was the source for that info?

Reson i ask, i took some measurements and ran some figures, and the equation gives rates of 66lb/in for the El Camino coils and 99lb/in for the ZJ V8 coils.

Seems the constant should be 4 not 8, or you need to double you results. Wierd.

It's a page out of the December 2001 issue of 4Wheel & OffRoad.

The mean diameter of the coil would be the average between the outside and inside diameter of the coil.

The active coils seems kinda tricky to measure, but look at the pic.

The coil wire diameter should be obvious.

So....In the example (blurry text part of pic) :


"Coil spring rate for a coil spring that has 12 active coils, with a coil wire diameter of 0.5 inch, and an average coil diameter of 3 inches would work out as follows"

Then they plug in the values:

(11,250,000 x 0.5^4) / (8 x 12 x 3^3) = 271 lb/in
(11,250,000 x .0625) / (8 x 12 x 27) =271 lb/in
(703,125) / (2592) = 271 lb/in

Math works out for me... try plugging in your values in the above manner...

Yea, I ran their numbers to check i could still do simple Algebra (had me worried).

Here are my numbers - check my math.

69 El Camino Coils

(11,250,000 x 0.579^4) / (8 x 11 x 6^3) = 66.51 lb/in

ZJ V8 coils

(11,250,000 x .590^4) / (8 x 16 x 4.75^3) = 99 lb/in

Yea, the # of active coils might be off by 1 or 2, but that's not going to half the result.

I dunno??

Thats the right equation BV, but the number of active coils is tricky, on a zj or xj, the top pigtail coil is dead, and probably most of the bottom coil is dead, so you should have about 2 dead coils total, basically any coils that are touching the mounting surface is not going to be active. The value for the modulus can vary, but 11,250,000 is a good average.

Bill..

The math is correct. Had me puzzled as well, so I did a search for spring rate calculators and found this site...

http://www.proshocks.com/calcs/index.htm

clicked on the "New Coil Spring Rate Calculator" link, and plugged in your values. Came pretty close.


Also stumbled across this link:

http://www.rapidline.com/calc/index.htm

Has some awesome looking stuff for the serious builder, but of course ya gotta pay for it. You can buy what you need , though.