GT500

Someone should really step it up and offer 4.30's also!

masterd78

I'm running the stock 4.10s with my 37's and using the AEV Procal to adjust shift points. Works like a charm, and I can easily live with it.

T3KN1NJ4

Hmmmm speaking of 37's I have 4 37" BFG AT with 95% tread left that I am looking to trade for 35's or sell for a good offer. I was using 538 and worked well

181

I've got the 4.10 in my '12 JKU auto and stock I feel that it is geared too low for a daily driver. I'm pulling over 3000rpm at 75mph. I too was wondering if I could get away with 37s on stock gearing with a procal and a chip. Looks like 37s would cause a 13.5% drop in effective gearing over stock making for about 2300 rpm @ 70mph. Its just the extra weight i'm not sure about. Can you elaborate on the feel on acceleration and holding speed on the highway.

borracho

Thats my feeling too. I got into an arguement with one of the workers at 4Wheel parts here that kept insisting that I'd need to swap gears to at least 4.88s on the 12 auto. I ended up just dropping it.

FWIW the arguement was dealing with 35s, not 37s.

JayRud

I've got 5.13's for my 37's (2012 manual). I like the extra power. The Jeep is not my daily driver but the RPM's would allow for that I believe. Goes down the freeway at about 3000 rpm at 70mph I. Need to double check that tho. 3000 miles with this setup and no regrets. 14 mpg on the freeway

VETTETHRET

I just had my lift installed this week with 38x15.5x18's on a Rubi with 4:10's and Im on the fence if Im going to regar at all, I am shocked. And I come from the world of multiple 1000 hp Vipers and Vettes.

As said by current owners of 2012's, the motor and tranny are LEAGUES above the previous 3.8 (And I owned 2 of them)

Christarp

4.88 on a 2012 auto are way too low of gears for 35" tires. You'd be better off with 4.10s to be honest.

StrizzyChris

Just a warning to the OP you are gonna get a ton of people commenting oh here with no actual knowledge of the new engine and will be giving you advice based on the 3.8 and probably tell you 5.13 or 5.38. Just dont jump the gun and buy before making triple sure the info is correct!

JayRud

Here is how 5.13's and 37's are working for me:

This is my setup: 2012 manual tranny, 37 BFG km2's, 5.13 gears. I have made the necessary changes w the procal. The factory specs on the km2 measure 36.8. A little smaller than 37.

Here are the highway RPM numbers:

60mph = 2300 rpm
65mph = 2500 rpm
70mph = 2700 rpm
75mph = 2900 rpm

MPG showing 16 mpg at 65 mph, 14mpg @ 70mph, 12mpg at 75mph (on the vehicle info readout). I'm happy with that since I don't give a rat's #@# about mileage. If I did I wouldn't be rolling on 37 inch tires.

Sounds like most are going to go with 4.88's for 37's with the new manual 3.6. I think the 5.13's work well though. Especially for wheeling, steep highway roads, or towing.

Chime in here if I'm missing something.