CelticMonster

Good day everyone, another question from someone who wished to learn (and is seeing contrasting info online).

I put up another thread about upgrading my current Dana 44 axles for the new wheels and tires (17x9 with 4.5" back spacing wrapped in 315/ 70 R17 BFG All Terrain T/A KO2s), but this time I want to speak specifically about gearing in an effort to avoid too many tangents on the other thread.
That said, here's the Jeep info: 2013 JKU Rubicon, auto transmission. Going to be a daily driver (including some highway use) and weekend warrior.

Here are my points of interest. I am between a 4.56 and 4.88 ratio and leaning towards 4.56; what are your thoughts?
Now in regards to installation... should I go for a standard or master install kit? Money is a parameter but I also don't want to purchase crap and expect gold in return. I want to do what's right but not overkill.
Thoughts?
- Thank you,
CM

jtphoto JK

Seeing how it is a 2013, I suggest the master install kit which includes new bearings and shims. You will need a new pinion bearing anyway so may as well change them all. I suggest 4.56 for your use.

resharp001

^^+1. If you're going to open it up and pull everything out, do master install kit and replace everything. This is not an area to skimp on a few dollars.

You have omitted what size tire you are running and/or are planning to run and current gearing. We see your in Oregon terrain wise. If you're running 35s and are currently on 3.73 gears, I'd stick with 4.56. You can go with 4.88's, but it's going to lean towards the aggressive side. Highway speeds are going to be revving some decent RPMs, close to 3k give or take. MOST people wouldn't prefer that, and it will eat in to fuel economy even more. 4.56 would be nice all around for DD and offroading.

If you're on 4.10 gears, you typically need to move 2 gearsets to make it worthwhile financially, so 4.56 doesn't make as much sense.

If you're on 35's and even THINK you might go to 37s, that could be the tipping point to consider 4.88s a bit more. Just my 2c.

CelticMonster

Thank you both very much. That is what I was suspecting but I needed some additional info to make the decision. I appreciate the input!
- CM

resharp001

Fortunately we have limited gearing to choose from (making the choice a bit easier), and there can be significant jumps between each. Moving only one set, say from 4.10 to 4.56, although might be perfect performance wise, might not make enough difference to justify the financial outlay. Hence, the rule of thumb being you have to move 2 sets to make it worthwhile (assuming you're paying to have the job done).

I'd also note that you have the benefit of Rubi transfer case for off road purposes which makes the decision even easier. For someone like me without that 4:1 TC, I geared a little lower for some offroad advantage as well. I run ~3k RPM at interstate speeds, and I base my opinion on the fact that can get a little aggravating at times, and why I say "most" people wouldn't prefer that, especially for a daily driver. Now, there will always be exceptions.....like someone that lives in the mountains and might never see 75mph on their speedo.

If you look at the gear charts for the 3.6L, they are pretty accurate. The charts take in to account the ACTUAL tire measurement, not what's stamped on the sidewall. A good test is to force your auto in to a lower gear on the highway and see what cruising at 3k rpm is like for a good while. Nobody will complain about having additional low end power, but the high end is were the lower gearing will start to get you.

japatton@icloud.com

Resharp pretty much summed it up. I’m currently running a 2013 JKU with an auto and 315/70-17 tires and 4.88 gears. I’ll be moving up to 37’s next, so I have already geared it down. If you are planning on sticking with 35’s and already have 4.10 gears, you’ll be fine. I had 4.10s and never had an issue on or off-road. Stick with that setup and save your money. Currently, running 70 mph I run at about 3000 RPMs. It’s a blast to drive around town, though!!