40"s on mildly modified JL Rubicon axles?

[J0E]

38x13.50-17LT Mickey Thompson BAJA PRO SX. They are only 9 lbs. heavier than my current 35" Trail Grapplers, so it should not be a catastrophic difference. But still probably would add trusses.

It's not the tire weight, it's the weight of the vehicle and the radius of the tire. And truss is just needed for KoH and bumping, has nothing to do with radius of tire.

Killer tire. That's about the limit of a D44 if you don't bump it or go too low in the differentials.

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[OBJLU]

The truss is going to help reduce deflection too, so will a high quality diff cover like the ARB.

 

[Headbarcode]

It is almost time to replace my 35' Nitto Trail Grapplers. I have had them for 2 years, love them, but still wish I had chosen 37" at that time. Now I am thinking if I get 37', I will wish I would go for 40"! I know there is no real need for me to do that, but hey, just wanting them is a good reason

Anyway, what you guys saying makes a lot of sense and I don't want to get stuck in the middle of British Columbia's nowhere. Thanks for all input. And since I am not paying 20k+ for new axles now, I am thinking of a compromise:

38x13.50-17LT Mickey Thompson BAJA PRO SX. They are only 9 lbs. heavier than my current 35" Trail Grapplers, so it should not be a catastrophic difference. But still probably would add trusses.

I was looking at that exact tire a while back. What knocked it out of the running for me was it being bias ply and having a directional tire tread. Bias ply tires don't like high speeds and fast maneuvers, but those aren't wrangler attributes. The directional tread was the bigger turn off. The spare would only be a proper fix for one side of the vehicle. It could be used on the other, but would require a run to the tire shop asap to have it remounted and balanced.

 

[Remorseless]

It is almost time to replace my 35' Nitto Trail Grapplers. I have had them for 2 years, love them, but still wish I had chosen 37" at that time. Now I am thinking if I get 37', I will wish I would go for 40"! I know there is no real need for me to do that, but hey, just wanting them is a good reason

Anyway, what you guys saying makes a lot of sense and I don't want to get stuck in the middle of British Columbia's nowhere. Thanks for all input. And since I am not paying 20k+ for new axles now, I am thinking of a compromise:

38x13.50-17LT Mickey Thompson BAJA PRO SX. They are only 9 lbs. heavier than my current 35" Trail Grapplers, so it should not be a catastrophic difference. But still probably would add trusses.

lol, fair enough "Because I want to" is definitely a valid use case! But yeah, it's not so much tire weight (IMO anyway, sure there are people who will disagree), but it's a combination of a lot of other things that are the consideration for axles - larger tires offer more leverage against axle components (a 38 is 19" worth of cheater bar torquing at the hub, 40s are 20"), vehicle weight is a huge component for whether or not an axle tube is sufficient, how much power you're sending to the ground, and how "hoppy" you are/how much skinny pedal you use off road. Those are more important to axle longevity than is tire weight, again, just in my opinion.

If you're not trying to smash through a rock garden at 20 MPH I think those'd do fine on a D44 provided you crawl hard stuff and avoid bouncing as much as possible (not always possible, but minimize it to be sure). However, @Headbarcode makes good points about the attributes of that particular tire. Driving home on a bias ply directional spare on the wrong side isn't going to like be catastrophic, but won't be great for the tire or how it drives. Just something to consider, looks like they'd pull great off road though.

 

[J0E]

I was looking at that exact tire a while back. What knocked it out of the running for me was it being bias ply and having a directional tire tread. Bias ply tires don't like high speeds and fast maneuvers, but those aren't wrangler attributes. .

And bias tires last about half as long.

Bias have much stronger sidewalls. Sidewall puncture has to be one of the most common off road tire failures. When I go to D70s, Bias tires will join them.

 

[KHR Racing]

This is all good stuff!

 

[boston3111]

I know plenty of folks doing it but they like me have modified the axle so that only the housing remains, everything else is upgraded,

what I’ve done to mine

- Reid knuckles
- RCV
- Dyntrac Ball Joints
- steering upgrades
- truss and gussets
- ARB diff cover which also acts as a truss
- Dana 60 rear (5 lug 40 spline)

i ran 39’s like this for a year and a half and just upgraded to 40’s which are 1 lb heavier and an inch taller but soon I’ll have a 5 lug 60 out front too

Fusion hybrid tons for the win!! I have the same exact set you do. Waiting till next year to order the matching front.

 

[FreedomFur]

In order to do this with any sort of reliability, you will need to mod all the things. When I say all, I mean nothing factory should remain except maybe the carrier and spider gears. Even then, those little spiders aren't made to take the hit of a 40 locked up.

It's inadvisable for this tire size to be run on the factory housing with its small tubes, FAD, and ball joint size (chromoly or not, the cross section of the joint is not big enough). By the time you've invested in the ball joints, axle shafts, and the trusses to keep from bending things, you would already be in ProRock 44 territory. Short story is that a 40 needs a 60.

(Keep in mind, Dynatrac advises a max tire size of 38" for their ProRock 44.)

Also, I know RCV says they're guaranteed up to 43" tires. What no one talks about is that the warranty doesn't cover normal wear and tear. Normal wear and tear on a 44 size RCV with 40's is accelerated greatly.

Just because you can mount a 40 on a 17" wheel with a 5x5 pattern, doesn't mean you should. I get that people have run this tire on the factory equipment, but they're on borrowed time and one wrong hit from destroying axle shafts and R&P's. The right gear to run this tire is at the maximum the factory housing can accommodate.

Upgrade all the things or get a 60. With that in mind, I've seen a lot of 60's break using a 40" tire, too. Mostly U-Joints or shafts. The Super60 gear set is a tough bastard, but you'll need the thickness of the 60 housing to keep the R&P meshed properly. That factory 44 housing is a very flexible unit once you start torque multiplying in that 5.13/5.38 gear set range. The torque will greatly multiply since the tire will have an enormous amount of grip, especially aired down, compared to a 37" tire.

Don't forget driveshafts, steering, and brakes, too. The factory big brake kit is garbage above a 37" tire. You'll need aftermarket rotors and pads that can handle heat and fade.

PS - I'm running a 40" tire and would not have done so without the axles I purchased. I went overkill, but that's the idea. Over-build to make it home. There's no way I would ever consider running a 40 on factory axles. Even the transfer case is pushing it. It'll literally tear itself in half like a piece of paper if you hit something wrong. (I have a pic, for those that are interested in seeing what a 40 will do to your transfer case.)

I’d like to see that pic of the transfer case!

Couldn’t agree more with this thread. Even 37s on a ProRock 44 and factory rear Dana 44 can be pushing it. I am running mine on 4.56 gears specifically that way to keep larger teeth.

 

[chevymitchell]

I’d like to see that pic of the transfer case!

Couldn’t agree more with this thread. Even 37s on a ProRock 44 and factory rear Dana 44 can be pushing it. I am running mine on 4.56 gears specifically that way to keep larger teeth.

Gotta read the whole thread. I posted it on page 2.

https://www.jlwranglerforums.com/fo...ed-jl-rubicon-axles.96082/page-2#post-1991491

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