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Discussion Starter · #1 ·
I want to know, what gear ratio guys are actually running 37's to 40's on their 2012s.

1. Model (Rubicon, Sahara, Sport)

2. Transmission (Auto or Manual)

3. Tire Size (37's - 40)

4. Gear Ratio (4.88's- 5.38s)


Last, if you had to do it again, would you chose a different gear ratio? Ex. Had 35's and jumped to 40's and should have went with a taller gear.

Thanks in advance,

Pluke.
 

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On the chance you don't have this handy, check out this chart. While I don't have 37s, it helped me decide that 4.88 was the ratio I wanted for my 35s (on my auto 2012 JKUR).

I wanted a net performance gain. This combination puts me in the middle of the performance "blue river".

I'm guessing this is for the "other" JK in the family. 4.88 is what I concluded would be good if I swap to 37s. I have the AEV module, so it's just a simple tweak away. Good luck!

(I'll send you a higher res version by email if you need it)
 

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gears

I'm going to go with 5.13's, doing a 6in teraflex long arm with 40's, on a Gecko Green JKUR.
 

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How? The '12 is like 4 seconds faster in the 1/4 mile. There's no way unless the guy in the '12 can't drive.


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Maybe his '10 is juiced up, but I sure hope my '12 with 35s and 4.88s has comparable acceleration to stock (if not better). Sure, my rig is optimized for off-road use, but I'll be sad if Pluke's '10 could walk away from me! I had both a 4.0 and 3.8 -- neither impressed me on the road! :)
 

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Discussion Starter · #12 ·
Maybe his '10 is juiced up, but I sure hope my '12 with 35s and 4.88s has comparable acceleration to stock (if not better). Sure, my rig is optimized for off-road use, but I'll be sad if Pluke's '10 could walk away from me! I had both a 4.0 and 3.8 -- neither impressed me on the road! :)
its juiced for sure. and with your regear i don't have any doubt that you're 12' may be a little bit quicker.
 

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heh. it's not even all that powerful. our 2010 2 door beats it on our drag strip.
no but it's noticeably better. I don't want to get into that debate again. But i put a lift and 33's on my friend's '12 on sat. i drove my brother's 07 (with 33's but 4.10's instead of the '12's 3.73's) later that day and the 12 was significantly better.

anyway, back on topic. have they figured out the flash so you can regear the '12s?
 

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no but it's noticeably better. I don't want to get into that debate again. But i put a lift and 33's on my friend's '12 on sat. i drove my brother's 07 (with 33's but 4.10's instead of the '12's 3.73's) later that day and the 12 was significantly better.

anyway, back on topic. have they figured out the flash so you can regear the '12s?
Yes. Seems a few companies sell a solution. I was going to go the ProComp route, but chose AEV's ProCal Module instead.

Here:
http://www.aev-conversions.com/shop/shop-by-category/electronics/procal-module.html

To me, it falls into the cheap, effective, but primitive category. I'm settling for it. Frankly, I'm used to far more sophisticated solutions in the aftermarket (especially tuning import turbo cars). They'll come but, it will take time. For now it seems to get the job done.

In my case I'm relying on it to change my JKUR from 4.10 w/32s to 4.88 w/35s (speedo calibration). Other nifty things that I'll do include "one touch" blinkers, defeat TPM, and increased idle speed while performing winching operations.
 

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I'm getting ready to lift my 2012 JKUR auto and can't decide if I want to do the 4" TF with 37's or the 6" with either 37s or maybe 40's.

From those running a 2012 with 37's or 40's regrets, wish you had gone bigger? I hate to admit mostly pavement pounder. I always make it to Moab for Jeep safari, but don't get out much more then that. I only work 10 miles away from my house and don't go above 60 most days as the speed limit is 55 on the road I take.
 

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The only downside I can see with the 6" lift is going to be your front axle geometry. You will be fighting Caster & pinion angles. The 4" teraflex will fit 40's with flat flares no problem.
 

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The only downside I can see with the 6" lift is going to be your front axle geometry. You will be fighting Caster & pinion angles. The 4" teraflex will fit 40's with flat flares no problem.
Thanks, thats good to know. I will have to do a search on this forum to see some setup with the 4" flatties and 40s and see if I like it.
 

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It will fit. But it will rub a like a bitch even with flat fenders. Hell our 37's rub on our two door with flat fenders with 4.5" of lift.
I'm not a big fan of rubbing. Teraflex is having a show this Saturday so I'm going to go to it and hopefully a bunch of other JKUs are out there that I can see in person and get an idea of where I want to go with this build.
 
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