Put a d44 up front and run 5.38...

 

With flat flares and a 1" body lift, you can run 37s with 1" front and 2.5" rear extended bumpstops.

Without a 1" body lift, you can run them with 2" front and as little as 3" rear extended bumpstops if you get really busy with a sawsall throughout the rear fender well pinch seam.

Some of this depends on wheel backspacing. Less backspacing requires slightly less bumpstopping.

With an automatic and 3.73s, driving with the OD turned off puts you at the same engine rpm as 5.38s. So, run them for a while with stock gears, a Superchips, and OD off to get a feel for it.

4.88s with an 07-11 automatic are low enough for 33s, but not 35s or 37s.

You can usually find a take-off front Rubi D44 axle that has already been regeared, gusseted and sleeves, with chromoly shafts for about $2000-$2500.

It doesn't make sense to spend $1000+ on a selectable front locker and cable or compressor, $600+ on front chromoly axle shafts, $300 for front gears and overhaul kit, and $400 for labor to upgrade a D30, when you can sell yours and buy a used Rubi D44 for a lower net cost.

 

I have a 2008 JK X 2-door. Automatic Transmission, 3.73's, 4" RC Suspension Lift Kit, and Smittybilt XRC (non-armor) flat fenders. I do not have extended bumpstops. But from what I've read and heard a 4" lift and flat flares offers plenty of room for 37's. Is this correct? Thanks for the information and I will definitely keep my eyes open for a built Rubi take-off D44. Also, I just got my ATX Slab's with 3.5" of backspace and I am going with 37X1250R17 Nitto Trail Grapplers.

 

Springs do not keep your tires from rubbing on your flares and body when the suspension articulates.

For a properly set up suspension, bumpstops stop up-travel and shocks stop down-travel. (Certain applications call for limiting straps.)

Running 4" springs, without extended bumpstops, 35s will rub when the suspension is articulated offroad. So no, 4" springs without extended bumpstops and with flat flares will not work offroad with 37s.

Spring height does not directly matter.

I helped a friend set up 37s with flat flares on his JKU Rubi with no lift--other than a front 1.5" leveling kit. It required significant trimming of the rear fender wells, 2" front and 1.5" rear extended bumpstops.


On my 2 dr, I run 40s with 4" front and rear extended bumpstops, 4.5" springs, with flat flares, and no body lift. It required significant fender well trimming.

 

I still think I'm a bit confused. So with a 4" lift, flat flares, and 37's with wheels that have 3.5" of backspace, what size bumpstop should I go with? 2" in the front and 3" in the rear?

 

Regardless of spring size, to run flat flares and 37s on 3.5" backspaced wheels, with no body lift, you'll want 2" front and 3" rear extended bumpstops.

It doesn't matter whether you're running 2.5" springs or 4" springs. The springs only affect your clearance at ride height, on level ground. They don't affect the clearance when the suspension is articulated.

 

Planman... When you talk about "significant trimming" on your rig, what all did you need to do? A lot of pinch weld area cutting or far more than that? Did you have to alter the location of the flairs or breach the passenger area?

 

These are pics with what I needed to do for my 40s. 37s wouldn't need as much trimming.

I had to eliminate the lower rear bolt/attachment hole on each side, and I had to trim from the middle top of the fender well all the way back to the lower corner. I also had to trim the internal bracket in the rear fender well area.

You don't need to breach the passenger area. You may have to trim all the way up to the spot welds in the seams. You will need to trim Bushwacker or similar flares below where they bolt on.

 

PlanMan,
Got a write up on doing Upper Helldorado?

Love seeing JK's going through that trail.

 

Thanks. Working on a YouTube video tonight regarding this year's run.

This was my EJS 2012 run:

http://www.youtube.com/watch?v=jJypB8EcYoc&sns=em