MY 1ST THREAD ON THIS SITE SO HERE WE GO..........I HAVE A 2010 JK SPORT 4DR W/ 3.8L AND AUTO TRANS THAT I RECENTLY PURCHASED A/B A MONTH AGO..LOVE IT!!!!!!!!!! ABOUT A WEEK AFTER I BOUGHT IT I ORDERED AND INSTALLED A 4" ZONE LIFT AND SOME WHEELS TO GO W/ A SET OF 315/70/18 (36's) TOYO OC M/T's THAT I HAD JUST BOUGHT FOR MY PREVIOUS TRUCK THAT HAD ONLY A/B 5K MILES ON EM....I KNOW MY JK HAS 3:73 GEARS, WAS THINKING OF GOING W/ 4:56.. IS THAT TOO MUCH??? IM NOT PLANNING TO TRAIL IT FOR A FEW YEARS, STRICTLY STREET/DAILY DRIVER BUT I ONLY WANNA DO THIS ONCE... MY BUDDY HAS A 2012 RUB THAT HE JUS LIFTED W/ 37's AND HE WENT W/ 5:13....I DO TRAVEL ON HWY'S AND INTERSTATE PRETTY MUCH DAILY... LAST WEEK I DROVE ORANGE BEACH ALABAMA WHICH IS A/B 1 1/2 FROM ME ALL INTERSTATE AND HWY'S AND NOTICED IT GOING BACK IN FORTH OUT OF OVERDRIVE SO I JUST TURNED O/D OFF AND IT WAS FINE BUT I KNOW IT SUFFERED ON FUEL,,BEFORE LIFT/TIRES/WHEELS I WAS AVG'N 18.5MPG AND NOW 12.2 SO THATS THE REASON FOR CONSIDERING THE GEAR UPGRADE. ANY HELP WOULD BE GREATLY APPRECIATED.

 

I would suggest 5.13s. I drove mostly highway when I had 35s and 4.88s. 4.88s aren't enough for even 35s.

 

I would suggest turning caps lock off. 5.13's are a good call for a 3.8 auto on 35+" tires. You will find a couple threads with good info stuck right to the top of this modified area. The Faq's have some gear charts that are specific to the JK, broken down by engine and transmission. Measure the tires (measured, not mfg spec!!) and run the numbers. There is more to consider than just rpm, but that is a good place to start.

And, there are about a bajillion other threads asking this, so there is plenty of reading material if you don't get enough replies. Also, when you are reading comments, note the engine/transmission of the person replying. 3.8 auto vs manual have different gearing needs. And 3.8 vs 3.6 have different gearing needs.

 

did your mpg and rpm pretty much go back to where they were when it was stock??

 

i see you have Falken RM's...my jeep came w/ a brand-new set 265/70/17...they are a really good tire, ride great too, not noise

 

I have a 3.8l on 35's. I went with 4:88's. I think they are perfect. I can still run about 60-65mph and Im right around 2k rpms. There are a bunch of factors to weigh when choosing a new ratio. I live in AZ and there are quite a few hilly areas around here. The Jeep pulls much better up hill and doesnt kick out of OD as often. Many people have good luck with 5:13's as well. Between these two ratios I personally think its all subjective and personal preference. I towed a 92 Mazda 626 from Phoenix to Page AZ and was shocked at how well the Jeep did. On the longer/steeper hills it wasnt very fun, but on the fairly flat parts of the highway the Jeep cruised right along. There were quite a few times I didnt feel the car back there.

www.facebook.com/NewHorizonOffRoad

 

I went from 4.10 to 5.13 with 35's and I think it is perfect for highway driving and my mileage stayed about the same.

 

Consider, a lot of so called 35" tires are closes to 34" tires, such as my 315/75x16 Duratrac's, and 37" are closer to a true 35". This is why I am considering 4:88 if I stick with 315 but, 5:13 if I think I will go to 37.