2.5 vs 3.5 on JK? - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 17 Old 10-23-2017, 05:05 PM Thread Starter
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2.5 vs 3.5 on JK?

Hello Guys,
I've been drooling on MC game changer/RK X-factor for a while(probably will be 35's for tires. Maybe 37.... but probably 35's).

I know if I go 3.5, I probably need to change shafts. But, what seems like the next big thing is lower center for 2.5.
That being said, is there really a huge difference? Am I really going to roll off a toll road by going 3.5 when 2.5 would not make me?
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post #2 of 17 Old 10-23-2017, 09:09 PM
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realize that you never get advertised lift height. Some 3.5" kits are 5" on light jeeps and 2.5" will net you close to 4" so depending on your overall set up on the jeep and what you are going to be doing with it has more to do with it then the 1" difference.

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post #3 of 17 Old 10-23-2017, 09:48 PM
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Quote:
Originally Posted by mayhemna View Post
I know if I go 3.5, I probably need to change shafts. But, what seems like the next big thing is lower center for 2.5.
That being said, is there really a huge difference? Am I really going to roll off a toll road by going 3.5 when 2.5 would not make me?
If you're planning to run this off-road with any frequency or difficulty, you'll need to replace your drive shafts eventually regardless of lift height. Might hold on a bit longer on a 2.5" lift but I wouldn't make that be a big deciding factor.


No, there's isn't a "huge difference" between a 2.5 and 3.5 inch lift. There's really three classes of built JK's in my opinion (I'm sure others would have other threshold opinions). There's the mostly-stock class, 2.5-4" lift 35-37" tire class, and the 4-6" 40"+ tire class. Within any of these classes, the size of lift and tire doesn't really matter that much. You get only marginal capability improvements when going to the upper end of that range. When you jump to the next class you get a huge performance gain. That's just been my observation. Within one of those classes, it's more about driver skill than having the marginally bigger tire or lift. That is to suggest that I feel a skilled driver in a 35"/2.5" Jeep can do much better than a less experienced driver in a 37"/3.5" Jeep. But unless there is a huge discrepancy in driver skill, neither will come close to competing with a Jeep on 40" tires on wide axles and a 5" lift because it's in a higher class of capability.


So basically, assuming a super hard core 40" tire build is not on the table, I'd decide more based on what you want the Jeep to look like and behave like on the road rather than thinking too much about off-road performance. After all, there's always a slightly bigger rock to drive over! If you want a great highway ride with some better axle durability, go with 2.5" lift and 35's. If you want a bigger Jeep (be it for looks, the slight trail performance improvements, or just because bigger is better) then go with a 3.5" lift and 37's. Everyone has different goals, and there are benefits to taking either path.

Generally, people say when deciding between two close sizes, go with the bigger size or you might regret it and/or end up just buying the bigger stuff later.
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post #4 of 17 Old 10-23-2017, 09:55 PM Thread Starter
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I want to try 37's but I read too many articles about d30 and 37's and it scares the crap out of me.
Whether I go 35's or 37's, I'm going to regear regardless so I dont think there will be too big of a price difference for me but it seems like if I go 37's it'll put too much stress on the car.
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post #5 of 17 Old 10-24-2017, 03:33 AM
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Quote:
Originally Posted by mayhemna View Post
I want to try 37's but I read too many articles about d30 and 37's and it scares the crap out of me.

Whether I go 35's or 37's, I'm going to regear regardless so I dont think there will be too big of a price difference for me but it seems like if I go 37's it'll put too much stress on the car.

I believe that to be true, I'm running a 3.5" on 35's just for that reason. I don't want to put 37's on a d30, and I refuse to spend money twice. So I have no plans to "build" the d30, just biding my time until I save up for that prorock 44. (Should have bought a rubicon)


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post #6 of 17 Old 10-24-2017, 03:40 AM
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Originally Posted by chris36l View Post
I believe that to be true, I'm running a 3.5" on 35's just for that reason. I don't want to put 37's on a d30, and I refuse to spend money twice. So I have no plans to "build" the d30, just biding my time until I save up for that prorock 44. (Should have bought a rubicon)


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Actually, you SHOULDNT have bought a Rubi. Not for the front axle at least. The 44 up front is only a small step up from the 30.

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Last edited by Z-OR; 10-24-2017 at 03:44 AM.
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post #7 of 17 Old 10-24-2017, 06:03 AM
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Originally Posted by Z-OR View Post
Actually, you SHOULDNT have bought a Rubi. Not for the front axle at least. The 44 up front is only a small step up from the 30.


Depends on what your endgame is, I don't plan on running anything larger than 37" tires(maybe 39's) which should work just fine with a d44. Truss, C gusset, upgraded shafts. Should be perfect for what I want to do. And I would have started with the lockers already installed, would have just needed to regear( I want 5.13) a little bit better crawling ratio on the transfer case.


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post #8 of 17 Old 10-24-2017, 02:14 PM
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Quote:
Originally Posted by chris36l View Post
Depends on what your endgame is, I don't plan on running anything larger than 37" tires(maybe 39's) which should work just fine with a d44. Truss, C gusset, upgraded shafts. Should be perfect for what I want to do. And I would have started with the lockers already installed, would have just needed to regear( I want 5.13) a little bit better crawling ratio on the transfer case.


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We're on the same page here.

My point is that the front 44 alone is no reason to pick up a Rubicon. Obviously there are other considerations, as you pointed out.

:-)

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post #9 of 17 Old 10-24-2017, 09:57 PM Thread Starter
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Ive heard sleeving and trussing(just basically Artec armor kit) 30 should be pretty close to 44 but I haven't seen any proofs or stats.
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post #10 of 17 Old 10-24-2017, 10:08 PM
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Quote:
Originally Posted by mayhemna View Post
Ive heard sleeving and trussing(just basically Artec armor kit) 30 should be pretty close to 44 but I haven't seen any proofs or stats.
Short of a different center section, the housings are the same between the 30 and 44. So if you're talking about housing strength, then yes a built D30 is really the same as a built D44.

The gears on the other hand are not the same, and building the housing with sleeves/trusses obviously has nothing to do with changing this. I believe the JK D30 front has a 7.125" ring gear while the D44 front has an 8.5" ring gear. Big difference there.

Essentially, both axles can land a jump equally well without bending the housing (although, a better way to put it is they'll both bend equally as much when landing a jump ), but they cannot get bound up in the rocks and survive equally well.
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post #11 of 17 Old 10-25-2017, 08:49 PM Thread Starter
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Where would people reach that point of "get bound up in the rocks and survive"?
hardcore level? intermediate level?
I'm sure it will mostly depend on how they step on their gas and such but I'm curious about the... general results
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post #12 of 17 Old 11-12-2017, 04:10 PM
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I am running the RK 3.5 xfactor on my 2 dr JK. Been very happy with it. Had to upgrade the front ds but rear shaft is factory with no issues
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post #13 of 17 Old 11-13-2017, 01:49 PM
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Quote:
Originally Posted by Z-OR View Post
Actually, you SHOULDNT have bought a Rubi. Not for the front axle at least. The 44 up front is only a small step up from the 30.
Elaborate... are you saying the a stock D44 in the front end of a Rubi is crap, or that even a built Rubi front end is crap? I have a Rubi D44, sleeved, trussed, C-gusset, skid, gears, RCVs and all that shit... and it holds up great.

But seriously, why is a D44 front end crap? Just curious - the way half these guys praise them its interesting to hear a different approach on it.

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Old shit needs fixed. Facts.
Shit run off-road needs fixed. Fact.
Old shit run off-road needs fixed more often yet. Fact.
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post #14 of 17 Old 11-14-2017, 12:48 AM Thread Starter
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are those 35's or 37's?
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post #15 of 17 Old 11-14-2017, 09:21 AM
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Quote:
Originally Posted by Z-OR View Post
Actually, you SHOULDNT have bought a Rubi. Not for the front axle at least. The 44 up front is only a small step up from the 30.
Quote:
Originally Posted by mayhemna View Post
Ive heard sleeving and trussing(just basically Artec armor kit) 30 should be pretty close to 44 but I haven't seen any proofs or stats.
This is just nonsense. A dana 30 and 44 are lightyears from each other when building. It isn't about the housing, it is about the size of the ring and pinion. I don't care how you armor a D30, it isn't going to hold up to abuse with 37's. If you live in FL and aren't playing on rocks, then a D30 might be okay.

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post #16 of 17 Old 11-14-2017, 09:33 AM
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Actually the housing has a lot to do with the strength of an axle. Most ring and pinion failures are due to deflection of the housing that causes the gear mesh to become misaligned and causes chipping of the gears or total failure. proper trussing of the axle will make a difference however there are no real trusses for the JK axles that actually will prevent this deflection. They are more of a bridge that look good and are only trussing the length of tube on each side of the differential, they don't give any rigidity to the differential. Housings with big diameter tubes and a strong overbuilt center section are going to be the best route to go if you are concerned with actual axle strength.

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post #17 of 17 Old 11-14-2017, 10:38 AM
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2.5 vs 3.5 on JK?

Great points about the housing but if you put low gears in a D30 with that small ring gear, you dont have enough teeth engaged with the pinion. People go to D60s, 14 bolts, Sterling etc. for the gear size, not the hosting strength. But that comes with the larger axles.


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