Stock XJ Front Spring Rate Versus????

[crazy-apes]

What is the factory spring rate on a 2001 XJ (non-upcountry)? How about the resting hight without a load? I am looking at the new Rancho Rockcrawler Competition Springs for the Jeep TJ. The are 160 lbs/in and 20.5 inches long unloaded. How much lift do you think this will give? I understand that the OME 934 (ZJ) sprins are 180 lbs and 18.5.

Sincerely,

Curtis

 

[Eagle]

The factory manuals do not specify the spring rates, but I believe stock springs are around 180 pounds per inch. Rusty's springs are designed to ride soft, and they're 160.

TJ springs are shorter than XJ springs. Those springs probably won't lift your XJ at all -- they might even lower it.

You can't compare two springs just on the basis of the unloaded height. The wire diameter and the number of coils plays a large part in determining the rate.

 

[Jackhill442]

Front coils are 120 lbs/in, while rear packs are 160 from factory on all XJ's.

 

[Eagle]

Front coils are 120 lbs/in, while rear packs are 160 from factory on all XJ's.

120?

That sounds VERY soft. Source for this data?

Or was that a typo and you meant 220?

 

[MaXJohnson]

I think you'll find that the 120/160 rates quoted are "wheel rates" not "spring rates". The wheel rate takes motion ratio into consideration.

for the sake of discussion, assume your XJ weighs 3500 lbs. Approximately 55% of that weight is on the front end, or 1925 lbs. Half of that is supported by each coil; 962.5 lbs.

962.5 lbs would compress a 160 lbs/in spring ~6" = 14.5" compressed height
962.5 lbs would compress a 180 lbs/in spring ~5.35" = 13.15" compressed height

Measure the installed height of your existing springs and compare.

YMMV

 

[crazy-apes]

Well the exact specs are 20.25 free length, 160 lb/ft, wire diameter = .893, 13 total coils, and 11.63 active coils. Anyone have an idea how tall that would be?

 

[MaXJohnson]

Well the exact specs are 20.25 free length, 160 lb/ft, wire diameter = .893, 13 total coils, and 11.63 active coils. Anyone have an idea how tall that would be?

The wire diameter, coil count and active coils along with the mean coil diameter, which you didn't mention, are used to determine the spring rate. You already know this to be 160 lbs/in.

20.25 is 1/4" less than you mentioned in your first quote, so the compresses height would calculate to 14.25" rather than 14.5". This means the two different springs would provide essentially the same ride height. The TJ spring, having a taller uncompressed height, would be less likely to fall out when a wheel is in full droop.