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Unread 02-14-2013, 11:52 AM   #1
97TJSPRT
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Biggest Tire on Stock Axles????

Hows it going everyone, just sold my pride and joy TJ and moved onto a beautiful JK. Ive been searching around on the JK forum but cant seem to find an exact answer, what is the biggest tire the stock axles of a JKU Sahara can support? I understand im going to need to regear and lift etc, but what can the axles take?? Im hoping to run 37s, can they handle it or is that too much rubber??

Thanks for the help!

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Unread 02-14-2013, 12:04 PM   #2
RockyClymer
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IMO, if you have a JK, not a Rubi, then you have a Dana30 front end and I would think 37s would be a push on that axle if you do any off-road wheeling, but there are those that do. A lot of folks, including myself, run 35s on the JK with no problems. Some of us sleeve and gusset the front axle for more strength and some even use aftermarket axles (I use RCV chrome moly) to aid in strength...again, just a short opinion. If you have a Rubi with Dana44 front end, then the axle is probably OK, but the axle tube is the same as on a D30...so, sleeve and gusset is an option.
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Unread 02-14-2013, 12:12 PM   #3
xflstl
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Imho 37's are to much for Sahara stock axles. Unless you only drive paved roads and do so mildly. Again imho 37's require built D44's to be able to wheel, and even then you can break stuff real easy.
When I ran 37's I had built Rubi D44's, broke a rear pinion, chewed thru u-joints on the front axles until I went to RCV shafts. In the Sahara with a front D30, I would not want to go above 35's and even with 35's I would still want RCV's.. Just my .02 I am sure there are many folks out there that will tell ya diff. :-)
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Unread 02-14-2013, 12:17 PM   #4
awinski
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its been done, but it takes alot of building. if you're planning on running 35s, build for 37s, if you're planning on running 37s, build for 37s then poor some holy water on it. best thing you can do is wheel slowly, and carefully, they can make it, it just takes the right methods and knowing when enough is enough.
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Unread 02-14-2013, 01:05 PM   #5
SubAtomicGenius
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Dana Spicer specification for the D30JK is 32" max tires, and the D44JK Rubicon/Non-Rubicon is 34" max tires. Those specs are engineered on vehicle GVWR and "intended use." So, because they were engineered for smaller-than-preferred tire size - 35" tires or larger technically requires some sort of attention to some extent. Again, this highly depends on "intended use," the actual tire size chosen, tire weight (this varies dramatically between tire models) and your GVWR. In fact, most manufacturers of rings & pinions, bearings and lockers won't warranty their products if you run tires over the Dana maximum spec'd sizes - it's in the fine print (Yukon being one of them).

That being said, if I were to run 37's with confidence, and I intended on going offroad (rather than just mall-crawling), I'd run nothing less than a front D44JK Rubi with sleeves, gussets and possibly trusses or get an aftermarket D44JK, such as the Dynatrac ProRock or Tera44 at the very least. The rear D44JK Rubi/Non-Rubi should be OK.

Of course, with 37-inch tires you're also opening yourself up to other issues like: proper lifts with adjustable arms; steering problems; ball joint wear; upgraded braking; etc. Nothing that can't be fixed by throwing a lot of money at it, though.

Also, I'm of the opinion that RCV shafts don't belong in the D30JK. The weak point of the D30JK, just like any small axle assembly, is the small size of the ring and pinion. Dana spec'd them for 32" tires! I wouldn't want to put a bullet-proof axle shaft like an RCV CV shaft or a chromoly in a D30JK axle assembly while running a set of 35's (or larger) just to 'grenade' the ring, pinion and carrier/locker... I'd rather break the axle shaft.
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Unread 02-14-2013, 01:25 PM   #6
xflstl
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Quote:
Originally Posted by SubAtomicGenius View Post
Dana Spicer specification for the D30JK is 32" max tires, and the D44JK Rubicon/Non-Rubicon is 34" max tires. Those specs are engineered on vehicle GVWR and "intended use." So, because they were engineered for smaller-than-preferred tire size - 35" tires or larger technically requires some sort of attention to some extent. Again, this highly depends on "intended use," the actual tire size chosen, tire weight (this varies dramatically between tire models) and your GVWR. In fact, most manufacturers of rings & pinions, bearings and lockers won't warranty their products if you run tires over the Dana maximum spec'd sizes - it's in the fine print (Yukon being one of them).

That being said, if I were to run 37's with confidence, and I intended on going offroad (rather than just mall-crawling), I'd run nothing less than a front D44JK Rubi with sleeves, gussets and possibly trusses or get an aftermarket D44JK, such as the Dynatrac ProRock or Tera44 at the very least. The rear D44JK Rubi/Non-Rubi should be OK.

Of course, with 37-inch tires you're also opening yourself up to other issues like: proper lifts with adjustable arms; steering problems; ball joint wear; upgraded braking; etc. Nothing that can't be fixed by throwing a lot of money at it, though.

Also, I'm of the opinion that RCV shafts don't belong in the D30JK. The weak point of the D30JK, just like any small axle assembly, is the small size of the ring and pinion. Dana spec'd them for 32" tires! I wouldn't want to put a bullet-proof axle shaft like an RCV CV shaft or a chromoly in a D30JK axle assembly while running a set of 35's (or larger) just to 'grenade' the ring, pinion and carrier/locker... I'd rather break the axle shaft.
Pretty much agree with the above, one way or another you are always going to be chasing a weak point. With a rear D44/rubi with Alloy shafts I found out the hard way what the weak point was when you run 37's


But I am not a mild wheeler.....
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Unread 02-14-2013, 01:38 PM   #7
brianjw
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Even with 35s you'll be chasing the weak link all the time, just to get it to drive halfway decent on the street.

I'm running 35s on the d44 front and didn't want to wheel it until I replaced the ball joints, installed c gussets, truss and sleeves. Upgraded ball joints helped handling on road a lot, even with only 5k miles. Tie rod, track bar, and track bar/sector shaft brace were a huge help in handling as well. I'm still running factory axle shafts so I'm always conscious of that off road.

With 37s you'll really want axle shafts, and I would be concerned about spending money on the d30 with weaker internals. I'd say the rubi d44 with sleeves/gussets is a minimum, ball joints, axle shafts, track bar and tie rod upgrades, and possibly hydro assist and brake upgrades. But that's me. I'm going to keep over-building for 35s rather than under building for 37s. Reliability is more important to me than an extra inch of tire clearance though.
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Unread 02-14-2013, 02:16 PM   #8
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Thanks for all the help guys! much appreciated!
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Unread 02-14-2013, 06:42 PM   #9
RockyClymer
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On the other hand, I would like to upgrade my axle shaft and such for the D30 and grenade the DS U joint instead....cheaper and easier to replace this weak link. BTW, I wheel it hard and have for 3 years on the current setup and have had zero problems.. A lot has to do with driving skills and knowing when and how to handle the skinny peddle!
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Unread 02-14-2013, 06:56 PM   #10
SubAtomicGenius
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^^^ I totally agree with you - driving skills and understanding how the axle assemblies/drivetrain work while offroad is key to saving yourself from experiencing any damage. Unfortunately, not everyone is able to do this!
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Unread 02-14-2013, 07:14 PM   #11
CJsPerson
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I run 37s on my JKUR and several of my wheeling buds feel I’m under built. Just gusseted and re-geared.
However I seem to break my Jeep less than some of them. I prefer to let my gearing and traction get me through and I move to my winch before that “one more try” that seems to be a down fall.
Build to your driving style J
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