JLUR - 37" tire risks

[BigDill]

We bought our JL with a 3.5" lift and 37" tires already installed and since we got it I keep hearing 2 different stories...
1) JL Rubicon with a lift can fit 37" wheels and there should be no issues as long as you aren't going crazy climbing vertical walls or rock bouncing.
2) 37" tires without regearing or replacing axles is sure to break something.

Can any of you who perhaps have experience give me your advice?
A) Are 37" tires ok on factory JL Rubicon running gear?
B) If upgrades are necessary, what is the minimum that I have to do to not break something on mild trails?

PS this is the lift kit that was installed, if this is any help...
ReadyLIFT | 2018-2019 Jeep JL Wrangler 2-Arm Terrain Flex Lift Kit

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[GRAK]

It's how you use it yeah. For mild trails 37s are fine on Rubi, the oem ball joints will go out sooner fyi. Wonder if previous owner regeared it or not

 

[BigDill]

I

It's how you use it yeah. For mild trails 37s are fine on Rubi, the oem ball joints will go out sooner fyi. Wonder if previous owner regeared it or not

Don't know but I will definitely look into it. They are definitely much cheaper than new gears and axles. Thank you.

 

[roaniecowpony]

I've had my JLUR on 37s 3.5" Metalcloak lift for a few years maybe 25000 miles. It has Metalcloak steering and trackbars, 4.88 gears with a 3.6 automatic. I do rock crawling with it on some moderately difficult trails like the Rubicon, Moab, etc. I wouldn't run smaller tires for what I do with it. But it takes more maintenance to keep it roadworthy. Ball joints, trackbar bushings, etc, all require more maintenance, tires cost more, etc. It seems like I'm always working on it. Its time to work on it again. I've developed a mild case of death wobble which didn't self dampen and required me to slow down to correct. It all depends on what you want out of your Jeep and how much you are willing to pay.

 

[roaniecowpony]

To your question about 37s with stock running gear, there are those that do it and say it works fine and there are some that have had failures. One common failure is twisted rear axles. The front axle shaft failures from large tires are usually a U-joint failure from applying power while turned sharply. It just takes a lot more torque to turn larger tires. Installing chromoly axle shafts add a lot of margin for preventing an axle shaft failure. The other failures of the axles is the bent or broken housing. This happens from big impacts or bounces. It's all about the driving style and a bit of luck. If you drive hard, you can break the Rubicon D44 axles. But, if you're conservative, you may not have anything to worry about, even on some pretty tough trails.

 

[Ratbert]

That's not really much of a concern until you get above 37s.

 

[_olllllllo_]

To your question about 37s with stock running gear, there are those that do it and say it works fine and there are some that have had failures. One common failure is twisted rear axles. The front axle shaft failures from large tires are usually a U-joint failure from applying power while turned sharply. It just takes a lot more torque to turn larger tires. Installing chromoly axle shafts add a lot of margin for preventing an axle shaft failure. The other failures of the axles is the bent or broken housing. This happens from big impacts or bounces. It's all about the driving style and a bit of luck. If you drive hard, you can break the Rubicon D44 axles. But, if you're conservative, you may not have anything to worry about, even on some pretty tough trails.

I would rather break an axle shaft than destroy the ring and pinion. The axle as the weak point is a much cheaper fix than a gear set.

 

[3TV]

Like roaniecowpony says, driving style makes all the difference. I have stock axles and 4.56 gears on my JLUR 392 and have been doing moderate to difficult trails with it for 3 years and 24,000 miles now. I used a 2 1/2" Metalcloak lift and 37s for the first two years, and for the last year I changed to 4 1/2" Metalcloak springs and 40s. I have done every trail in Moab at least twice and the Rubicon 3 times with no drivetrain failures. Each of the Rubicon trips have been with roaniecowpony. I do have Metalcloak steering, sector shaft and track bar braces.

Roaniecowpony was right behind me on the Rubicon trips, so he may say otherwise, but the driving style I try to use is very light on the throttle. A 392 makes more torque when it is idling than a 3.6 makes at its peak torque. So, I generally do not need throttle on most technical sections of trail. I idle along and use the paddle shifters to increase or decrease speed. If I do need throttle, it is almost always limited to less than 1500 RPM. My driving is far from perfect though, and I did manage to scuff the passenger rear fender flare on a rock this year on the Rubicon. Actually, it felt like a fairly hard hit to the side of the Jeep, and I was surprised not to see more damage. And I damaged a RSE Stepslider badly enough to need to replace it and did some rocker panel damage this year on Cliffhanger trail in Moab.

I'm just saying the Jeep gets used, and no drivetrain failures. For your described use of "mild trails" I think you'll be fine. Expect to need more maintenance like roaniecowpony says.

 

[roaniecowpony]

I would rather break an axle shaft than destroy the ring and pinion. The axle as the weak point is a much cheaper fix than a gear set.

I dont want any driveline trail failures. But axle shaft failures on the trail are particularly bad on semi-float axles.

 

[Ratbert]

I dont want any driveline trail failures. But axle shaft failures on the trail are particularly bad on semi-float axles.

Wasn't "easier to fix on the trail" supposed to be a selling point of the new axles? Maybe I'm misremembering that, or was unknowingly mislead.

 

[TrailMax]

Wasn't "easier to fix on the trail" supposed to be a selling point of the new axles? Maybe I'm misremembering that, or was unknowingly mislead.

I believe the new axles are full float (e.g. the axles do not bear the weight of the vehicle), though just the rear.

 

[roaniecowpony]

Wasn't "easier to fix on the trail" supposed to be a selling point of the new axles? Maybe I'm misremembering that, or was unknowingly mislead.

I think you're right about that on the later JLs with the rear "full float" axles.

My approach on the D44s on my 2018 is to put in chromoly axles and mitigate the probability of having a failure on the trail. I could deal with a ring and pinion failure easier on the trail than an axle failure. That's because, although I have spare axles, I rarely carry them in the Jeep, but they are sometimes at or near the trailhead, along with spare driveshafts, tierod, draglink, trackbar, D44 differential, etc.

 

[Ratbert]

I think you're right about that on the later JLs with the rear "full float" axles.

My approach on the D44s on my 2018 is to put in chromoly axles and mitigate the probability of having a failure on the trail. I could deal with a ring and pinion failure easier on the trail than an axle failure. That's because, although I have spare axles, I rarely carry them in the Jeep, but they are sometimes at or near the trailhead, along with spare driveshafts, tierod, draglink, trackbar, D44 differential, etc.

Yep, I was confusing full float and half. My bad.

I've been pretty foolish by not bringing spares along. I have, however, wheeled with Toyota people that bring lots of front end replacement parts. It's surprising how often then have to crawl under to replace stuff.

 

[roaniecowpony]

Yep, I was confusing full float and half. My bad.

I've been pretty foolish by not bringing spares along. I have, however, wheeled with Toyota people that bring lots of front end replacement parts. It's surprising how often then have to crawl under to replace stuff.

I'm amazed how many jeep people run D30/D35 axles with 37s and don't seem to have problems. I would think the Rubicon trail would eat them, but I seem to be wrong.

 

[3TV]

I'm amazed how many jeep people run D30/D35 axles with 37s and don't seem to have problems. I would think the Rubicon trail would eat them, but I seem to be wrong.

I broke a Dana 35 rear axle shaft on a '95 YJ once while pulling out of a gas station. I wasn't even giving it the gas beyond just normal mellow acceleration. No tire spin or other shenanigans, just pulling out and turning at the same time. I hear a loud bang and feel the rear of my YJ shift. When I looked in the passenger side view mirror, I see my tire and wheel about 6" out from the fender flare, so I pulled over and stopped before it came all the way out.

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