larry0071

I have been on 37x13.5 STT Pro tires for a few summers now and I am at least pondering the move to 40" tires.

Currently using 3.5" Rock Krawler triple rates, 1.25" body lift, Ram Assist on a ProRock 44 Unlimited with Eaton E-Lock, Sport D44 rear with TrueTrack and Ten Factory shafts, 28" Fox shocks, factory control arms, Fusion 2.5T Tie Rod, Synergy drag link brace/Pitman brace, Synergy track bar and 4.88 gears with a Rubicon 4:1 T-Case.

My JK is not a daily driver. It is trailered to and from the trails and driven as desired to work and for errands.
I am not a flip/high steer, I expect that I need to swap to 4.5 RK springs and high steer.
I am using a D44 rear, I expect that I'll need to move to a D60 rear.
I play at Rausch Creek and like to run black and red rock trails, things get somewhat bouncy and nasty before I pull cable.
I expect to increase shock length to match longer coils, likely around a 30-31" extended front shock, 28-29" rear because of the EVO rear shock raise brackets.
I am on factory brakes now, but have a front and rear big brake kit (Dynatrac ProGrip) already paid for and ordered. So brakes should not be an issue.

My current build on 37" rubber has been essentially bulletproof. I am not real nice to my Jeep, yet it always drives me in and back out. I would like to maintain that relationship of reliability while hammering around on the rocks.

So to those of you who have built quality 2 doors on 40's, what am I not thinking of? I am thinking that the PR44U with RCV shafts is going to be marginal, but should be okay...

Please offer your experience and knowledge to help me decide if this next evolution is more than I want to fund or not. I prefer to pull it apart 1 time and pull it out done right and not have to mess with it again. My 3 years 16/17/18 have been totally hands off aside from brakes, greasing and swapping out a couple bent factory control arms.

BoraBora

Dunno how well that Eaton will fare with 40's. I nuked my 30 spline 4 pin Eaton rear with 37's just 2 weeks ago. I'd look into a 35 spline conversion for the front. Should be pretty easy to offload the 30 spline RCV's and locker anyways.

Another note, you sure you need more lift height? I think you can cram those shocks (11.8" travel front, 10.5" travel rear....or "4-6 inch lift shocks") with what you've got now. I'm running around 3-3.5" of lift on 37's with the shocks I listed (28" extended rear, 28.3" front) with 2" front and ~2.25" rear bumpstops with the EVO Rockstars. I'm also running flatties. I'd imagine with a 1.25" body lift like you, I could fit 40's no problem. Just shooting ideas around.

TOTL Innovations

With a 1.25" body lift on top of a 3.5" lift, I dont think you will need any more lift.

What backspacing are those wheels?

larry0071

The wheels are a discontinued LRG model 106, part number 10689073700
18"x9"
5 on 5"
Offset 0mm
Hub Bore 83mm
2500 LB rating per wheel
So with 0mm offset, that gives a centered hub at 4.5". I do also run a G2 1.5" wheel spacer, so that moves the wheel mounting surface to a 3" offset.

I purchased these because of the easy access to clean the barrels, I will only buy a wheel that my hand can fit through with a wash mitt for easy cleaning.

TheDirtman

Axle width is going to be an issue. Figure another 2.5" of effective wheel backspacing needed. Or go up big in height 6"+ so you can steer.40's on 44's is just a poor idea and reliability will go out the window. Trails will be super easy and you will try harder and harder trails you could not do on 37's pushing the other components harder then you ever have before. Moving to a rear 60 mens new driveshaft or at lest have yours cut down. Typically a lot of money and work to make the move and its up to you if you think you need to spend $15-20k so you can climb that bigger rock.

TOTL Innovations

Yeah thats not enough back spacing and as someone who made the jump from 37s to 40s, I would agree with Dirt on this one. Its also going to take the fun out of things because you will need some pretty serious obstacles to make it a challenge.

resharp001

I've told myself I'd never make this jump........and every time I even let the thought drift in to my head, I have to remind myself I'd have to park outside the garage, cuz I can't spare even 1" of added height before I won't fit in! That said, what I have seen first hand is a couple friends go this route....build and build, end up on D60s and 40's, superchargers and all that fun stuff.......and now, they never get out to wheel, and it pretty much plays to what Dirtman said above. Now they own some really nice rigs, but never use em.

jedg

I'll echo the same. I've found that 37s are just right for me. It allows me to play at the fringes of the 'big boys', I can go out with the fellows on 40s and mostly hang with them (though it's more of a challenge for me) and I can still go riding with the folks on 35s and have fun. Also, I attend Jeep Jamborees on occasion and they have a limitation of 37 inch tires so this keeps me eligible for their functions as well.

I'll say that Dirtman and Planman are the two that have kept me level headed on the show lift/tire thing. I'm still happy with the coil spring/shock suspension and 37s.

Dynatrac

It's very wise of you to give this careful consideration before diving in. Going to 40s is a significant step up in what's reuqired to ensure that you have a reliable rig. One thing that stood out in your original post is that your rig is pretty much bullet proof now and very reliable with 37s. When you go to 40s, you'll really need to upgrade both axles at least to ProRock 60s and a full-float rears to remain bullet proof. People can get away with running a 44-class front axle with 40s, but that's not the same as having a bullet proof rig that you know won't let you down and ruin a four-wheeling outing. In addition to the additional strength, as others pointed, you'll want wider axles to push the wheels/tires out and allow you to run wheels with deeper backspacing. With 40s on a 2-door JK, we normally suggest our Hard Core Plus ProRock XD60/XD60 axle combo. These are the strongest 60-class axle you can buy. The front XD60 also includes our 1550LT wheel ends that allow you to have the best turning radius and lowest stress on the rest of the steering components. Hope this info helps!

larry0071

That pretty much ends it for me. To go wider is really a bad idea being that I live in Pennsylvania and we are not allowed to have tires outside of the fenders at all. I am already illegal by having about 2" out each side, but it's not so vulgar that the cops harass me. I'm sure that if I went wider and had nearly 4" of tread outside, I would get to know the police in PA who have a hard on for enforcing that law. I get nervous now when a cop is following me... It's not a money thing as much as a worry free legal thing. As I am now, my wife and I pass the Jeep back and forth as a nice day vehicle that we drive to our jobs, I have had the doors and top off for about 3 months now. It sets in a garage until there is a low/no chance of rain and then we take turns with it. The last thing I want is a pissed off Momma calling me to explain that she just got ticketed or towed by some police who hates Jeeps. And anyone in PA can tell you, there are areas known for targeting Jeeps with doors removed, tires sticking out, LED light bars and more.