Just thought I'd post this for any new 2012 guys that are thinking of regearing. I still wish I'd gone with 4.88, especially after averaging 13mpg (@ 77mph avg speed). I drove from Denver to Lawrence, KS and averaged about 13mpg on I-70 with the 5.13 on 37s with auto trans. The 200-300 rpms you would drop by having 4.88 IMO would make a significant change in the mileage. After 5000 miles with the Pentastar and 37s combo I'd recommend:

5.38 (Rubicons) - Trail only, auto only. ***manual trans will rev, clutch dump and grenade the D44 diff with this HP. You will blow it up, just a matter of time.***
5.13 - Drivers that mostly town and trail drive.
4.88 - Drivers that drive a fair amount of hwy and want a good gear ratio for all types, including trail.
4.56 - Drivers that make significant trips on the highway with regularity, but still tool around on moderate offroad trails.

This being said, I make 2-3 trips a year back to the KC area and I just prefer to drive my Jeep rather than her car, and I really do wish I'd installed the 4.88. The Pentastar has good power, enough to spare without killing offroad performance by going to a 4.88.

The new Jeeps just don't compare to the 3.8L guidelines for gearing. Apples and Oranges.

 

If I were running stock gears and just wanted to reduce the unsprung weight of the oversized tires, then yeah, I could just run stockers. But, when you regear, if you throw some 32" tires on a 5.13 geared Jeep, you'll do the opposite and cruise the highway doing 80mph at like 4000 RPM and getting 9mpg. What i need is a set of 37" street tires, 4.88 gears and a gigantic lightweight cone to strap on the front for some aerodynamic improvement.

 

Yep, if you can find a drafting friendly one!!

 

I got 3.21's with an auto and 35's.... It still hauls a$$ like normal... I have ZERO plans on regearing

 

I was running pretty high psi and honestly, unless you get back in the green at 65mph with the 5.13, you're looking at sub 14mpg. I've had nothing but jeeps for years, I know they don't get crap for mileage but I had hopes for the Pentastar over the 3.8 even after going big.

As for the clutch dump, I'm talking about average drivers not used to that sort of torque, caught on big hills, panicking and dumping it at 5k rpm. Kaboom. Of course you won't blow it up if you're already in gear and crawling. The 5.38 would just be massive overkill if it ever touches pavement. Totally unnecessary unless you trailer it. My 2009 was 5.38 and just fine, but I wouldn't EVER gear the 3.6L to 5.38 without running 40s, just not needed at all.

 

I can see that being low when 4.88 gears with 35" tires would get you about back to stock being similar to 4.10 gears and 32 inch tires. 40's would put you back to stock as well ratio-wise, but it might be tough on axles and drivetrain.

 

This pretty much coincides with the data I put together that can be found in the FAQ. I definitely feel your pain and the rules have definitely changed now that we have an adequate powerplant.

 

Just drove 1400 miles in the stock rubi and man was it awesome! 20MPG the whole way. Personally tired of lifted jeeps. The stock Rubicon is plenty capable stock.

 

Congrats on the new Rubi

 

i agree. my only mod is a 2" lift, still stock tires and got 20 mpg on the highway with 4:10s. awesome performance off road too, no reason at all to regear with stock tires and probably not with 33s or even 35s with the auto. the first 3 gears in the auto are a lot lower than previous years, and the 5th gear OD is also lower - meaning lower crawl ratio but also higher rpms at speed than the previous autos.