I have a 2011 JK Sport (2 Door, Auto, 3.73's) and I plan on jumping up to 33's soon and possibly 35's in a few years. Most of my driving is on-road with the occasional light off-roading (nothing extreme), I do plan on doing a fairly good amount of towing.

Soooo...what gearing should I get, and should I do it before 33's? or after? I was leaning toward the 4.56's right after I get the 33's fitted but I'm not sure if towing will have a pos/neg impact on that decision. Any suggestions???

 

I would just try everything with your 3.73's and 33's for a while and see how you like them; they maybe tolerable for you.

I ran 4.10's and 37's for over two years and they weren't bad at all.

 

Man... I dont know how many times I have preached about this.

4.88 is your only choice.

My bud with an Auto Rubi w' 37's, Superchips, and 5.13's hated me when i blew his doors off
at a Jeep event in Daytona with everyone looking. lol it was awesome.

I have a 6sp, 4.10's and 35's.

My point is... the JK engine literaly beggs for higher rpm's... give it to her!

If you want to go bigger in the future, consider a 5.13

 

I have a 2010 JKU Sahara (4 Door, Auto, 3.73's) and just put Yukon 5.13s in and I LOVE THEM. I'm running 33s and will get 35s when these wear out. I can run 65-70 on the interstate and never jump out of overdrive. I pulled a 2000 lb pop-up camper 500 miles (interstate) and got 14.2 mpg. My gas mileage has increased about 1.5 mpg all around since installing them. The Jeep is way more responsive. It's by far the best mod I have made.
I LOVE THEM.

 

I have a jku with 33s auto and 538s originally had 488s hated them still no power and would not pull a small trailer, 538s is the way to go with an auto and 33s 13-15 city and 15-18 highway... Makes the jeep fun to drive again!!! Good luck I was in your place 4yrs ago doing the research asking questions getting opinions just make sure you ask if the opinion has an auto or manual the OD gearing are much different .84 in manuals and .69 in autos in my opinion they are way different beast... The Autos should of come from the factory with 456 to get the power to weight ratio better aligned... IMO

 

wow, 33s with 5.38 gears in 4th is identical to 33s with stock 3.73 gears in 3rd. On the highway, wouldn't it have been cheaper to stay stock and just turn your OD off?

 

But if you really think about it... stock is not good at all, poor gearing and shift patterns.... then adding a little taller tire and extra weight, lift, bumpers, winch, and pulling a trailer... the 538's have been great. With the 488's I had a 2-3 mpg less than i do now. IMO the bigger gear helps the weak 42r transmission work more efficiently and I still have ALL my gears available even when pulling the trailer...

a while ago I posted some rationale for a stock JKU with an auto to have 4.56 from the factory... I took the 2002 Liberty as an example before Jeep decided to change the transmission to the 42r which previously it was only used in the 4cyl liberty models... similar wgt, similar motors., different OD's, smaller tires, and same 3.73 gear... just never made sense to use a small V6, loose gear ratio transmission with a steep OD and then put 32" tires on... I can see why the '12's and overseas diesel run a close ratio auto trans and bigger OD similar to the manuals... it just make sense with the size of the tire and axle ratios available...

The real killer in the 42r is the OD, .69 and the 32" tires... not necessary the 3.8L.... look at the original Willly's Jeep Go Devil had 60 horses, with 5.38 gears and 700-16's (30-31" tire).... do the math, it would pull anything... I would like to see a company that would make a kit to change the 42r OD to being closer to .80... not sure if its possible... Or a transmission swap would also be nice - W5A580 swap... Interesting that the Jeep Commander has the same JK 3.8L but used the W5A580, so jeep has the ability to make the change and the trans programing to make it work in the 07-10 JK's... RECALL????

 

I agree with 5.38's being awesome. I run them with 33's for now, as I plan on a larger tire size in the future when the KM2's wear out. Living in a hilly area, there's really no other option if you have a rubi or have swapped in rubi 44's. But since you haven't mentioned that you have done that, go 5.13's. You won't be disappointed. Don't be afraid to run that engine where it's happy (higher than stock rpm). It's better on the engine and trans to not have to struggle and bog down than to be hunting gears and being under constant heavy throttle.

 

Iv got a '08, auto, 2 DR, riding on 33's. I hated 3.73 gears. I could never use Overdrive, even on the interstate. I regeared to 5.13's and love it. I'm getting 17.5ish MPG on the highway keeping my speed steady at 72 MPH. The best part is I can pass people without downshifting, and I almost never have to downshift on the interstate for incline changes. Definatly no regrets over 5.13's for me. They are the best mod I'v done by far.

 

Not trying to hijack the thread... but definitely agree with jk-tony... the 3.8L loves the 2,300 rpm range, it just feels very happy there... with stock gears and tires, it always seemed way to sluggish and the motor just seemed very unhappy.... I read in a couple other 42rle transmission threads on this site that when the 3.8L is lugging the transmission TC is locked up in 3rd and 4th causing tons of heat build up in the torque converter... to paraphrase... viscosity of the trans fluid through the trans veins at low RPM's will cause heat build-up (cant confirm or deny - but sounds plausible and makes sense why so many 07-09's trans are overheating at low RPM's) so my guess is that if you can get the engine up in RPMs regularly ie go with larger gears this could save on overheating the transmission and potentially starting a trans induced fluid fire.... so, I am so willing to give up a few mpg to protect my investment and keep my family save on the road or at home.... IMO

Again IMO... 5.13's with the Dana 30 - 33's and if you have the D44 upfront 5.38's with 33's... I have wanted 35's, just wont have the same performance i have with 5.38's/33"s unless i can change the transmission to A580 - 5 speed auto...