Rear spring lengths

[99tjadams]

Hello all, I was a jeepforum member 20 years ago. Built up my TJ with a ton of help from the forum and then life and a trans am project got in the way.

Now I’m back and looking to fix her up again.

I need to lower it another 0.5” to 1” so that it fits better under the hoist. (Right now it’s aired down 0.5” to get in there and it’s still tight)

I have already removed the 1” body lift.
It has a rubicon express 4.5 with what are supposed to be 3.5” springs (I’m skeptical)

Also has a SYE, MML, ford 8.8, 4.56, Trxus 35x12.5R15

Going to a 33 or 34 (285/75/17) is an option but I would really like to keep the 35s - 90% street, 10% forest service roads

Right now my compressed spring heights
16.5” front (converts to 4.5” lift)
13.25 rear (converts to 5” lift)

Lots of rake, about 2” higher in the rear

Front left to fender 39.5”
Front pass to fender 39.25”
Rear left to fender 41.5”
rear pass to fender 41”
Low fuel, no tire rack or spare

Bottom of frame to floor 22”
Bottom of door to floor 32.5”

After a bit of reading here I am planning to replace the rear springs with Currie

Trying to decide if I should just replace the rears or replace all four.

Replacing the fronts with Currie 4” (15.75” compressed) should lower the front about 0.5-0.75”

Finally my question …..

The Currie rear springs compressed

Currie 3” rear is 11”

Currie 3.5” rear is 12.25”

Currie 4” rear is 13”

Why does a spring that is 1” shorter when compressed only drop the vehicle height 0.5” ?

 

[TheBoogieman]

Option #2.

 

[Inogame]

Dude.. tell me more about that bird...

 

[99tjadams]

Option #2. View attachment 619515

This is brilliant.

 

[99tjadams]

Dude.. tell me more about that bird...

76 T/A
455 , KRE heads, hyd roller
Tremec 6spd, 4.10s
I’ll try to dig up a pic

 

[lBasket]

Option #2. View attachment 619515

 

[TheBoogieman]

View attachment 619517

Damn foreigner. Those wheels are huge to @Kiwi TJ .

 

[99tjadams]

This post seems to explain it.
Post in thread 'Currie rear 3 inch springs seem tall'
https://wranglertjforum.com/threads/currie-rear-3-inch-springs-seem-tall.71643/post-1356704

Sounds like I should go by the compressed height spec, not just the “advertised lift” amount.

Probably going to go 3” TJ springs in the rear to bring it down 2”

Then see how it is, and likely swap the front to the 4” TJ springs. Should lower the front 0.5”

Should bring the frame down to 20” and windshield height closer to 6’2”

I curious if the ford 8.8 tube diameter is larger than the Dana 35 and that’s why the rear is riding extra high.

I’ll probably ask Currie what they think as well before ordering.

 

[jjvw]

Advertised spring lift height is only someone in an office guessing. They do not know how much your Jeep weighs.

 

[macleanflood]

I had a PO installed procomp 4" lift.

I replaced the springs with Currie 4" and gained two inches.

I'd weight your vehicle... preferably each individual tire weight, or at least front and rear axle. Then call Currie and talk to someone.

I personally would be lowering my Jeep on to HF vehicle dollies for the few times I'm on a lift vs compromising ride quality. Sure it's 10 percent FS roads but trees fall, landslide happen and you can never discount a good zombie apocalypse or civil unrest.

-Mac

 

[99tjadams]

I had a PO installed procomp 4" lift.

I replaced the springs with Currie 4" and gained two inches.

I'd weight your vehicle... preferably each individual tire weight, or at least front and rear axle. Then call Currie and talk to someone.

I personally would be lowering my Jeep on to HF vehicle dollies for the few times I'm on a lift vs compromising ride quality. Sure it's 10 percent FS roads but trees fall, landslide happen and you can never discount a good zombie apocalypse or civil unrest.

-Mac

I’m surprised you went up in height. Most people claim the RE/Pro comp lift gives more over advertised and the Currie is spot on.

I do have smaller wheel sets and HF Dollie’s, so it is an option. Appreciate the feedback.

 

[99tjadams]

This is what RockJock says

Loaded weights of our springs are tested at 690lbs a corner, not sure how yours equates to that

Our springs are lighter rates but they are designed around 35’s heavy bumper and hard top with full 35” spare.

I’m trying to think of a way to measure my corner weights. We have a 25ton crane with digital scale at work, but not sure how accurate it is around 1000lbs

The guy at the landfill is a grumpy old prick, I don’t wanna ask him to let me play with his scale lol.

Probably going to go with the rear 3”
Math says it will drop me 2”
But I’m gambling that I’m lighter than 690lbs a corner and it will only drop me 1-1.5” in the rear, which would be ideal.

 

[jjvw]

This is what RockJock says

Loaded weights of our springs are tested at 690lbs a corner, not sure how yours equates to that

Our springs are lighter rates but they are designed around 35’s heavy bumper and hard top with full 35” spare.

I’m trying to think of a way to measure my corner weights. We have a 25ton crane with digital scale at work, but not sure how accurate it is around 1000lbs

The guy at the landfill is a grumpy old prick, I don’t wanna ask him to let me play with his scale lol.

Probably going to go with the rear 3”
Math says it will drop me 2”
But I’m gambling that I’m lighter than 690lbs a corner and it will only drop me 1-1.5” in the rear, which would be ideal.

The rear Rubicon Express coil springs are a 225lb/in spring rate. They have a free length of 16.5".

Subtract their current ride height from their free length. Multiply that number by their spring rate. That number is a close estimate of your Jeep's rear corner sprung weight.

Use that number to estimate the ride height of any other coil spring with a known spring rate and free length.

 

[99tjadams]

The rear Rubicon Express coil springs are a 225lb/in spring rate. They have a free length of 16.5".

Subtract their current ride height from their free length. Multiply that number by their spring rate. That number is a close estimate of your Jeep's rear corner sprung weight.

Use that number to estimate the ride height of any other coil spring with a known spring rate and free length.

This is brilliant
I’m going to triple check my spring heights and run through this.
I noticed a 1/4” makes a big difference in corner weight.