Hi everyone,

I am looking to upgrade my tires to 37s or 38s. I have 2012 JKUR with a 4" teraflex lift, fox shocks, and Bushwacker flat fender flares. During the Spring, Summer, Fall I only drive my JK to Moab, San Raphael Swell, Escalante, Uintas, etc. It is pretty much for getting me to the trail and riding for a couple days at a time and driving home. I never drive it as a daily driver. Driving to Moab for instance, I climb up Soldier's Summit and a lot of other high passes.

During the winter, I have to drive it all the time. I live in Summit Park (Altitude 7,500') outside of Park City, UT where we get a ton of snow so my daily driver is garaged all winter. I am going to keep my current 35s for winter/daily driver use and switch to my 37s or 38s in the Spring. I have to climb Parley's Summit everyday (a pretty steep mountain pass in Utah) and my current setup is really slow and puts a lot of stress on the engine.

To my question, I have done a lot of research and have read countless threads on tire sizes and gear ratios, so I am really seeing if anyone could give me advice on what they think would work for my particular setup.

Do you think I could fit 38s with a 4" Teraflex lift and Bushwacker flares?
- Teraflex's website says 37s are max, but that might be with the stock fenders, not bushwackers.

What gear ratio would be best for 37s/38s?
- I have heard 5.13s are good for 37s (Do Yourself a Favor - Regear Your 2012-Up JK!!!!). If i can fit 38s, I definitely want to go with them, should I go to 5.38s. I can't find anything on 38s.

Thanks in advance!

 

That's a lot of gear. I've got 37s and 4.56s and I'm hitting around 2300-2400 at 70mph. To me they're perfect.

 

Which transmission? Does freeway rpm matter to you during the winter?

5.38's are pretty much for us poor guys with 3.8 auto's. Just plugging numbers into the charts, a 3.6 with 35's (that measure 34"?) and 5.38 would put you around 2970/3090 @ 70, depending on transmission. 38's (that measure 37") would be up around 2730/2840 @ 70. Probably a lot more rpm than you want.

Assuming a low enough backspace - you have plenty of room for the 38's. And you can always add taller bumpstops if needed. (the Thoughts on Lifts thread has some backspace suggestions.)

Have you looked into strengthening the front housing? Shopping craigslist for spare shafts?

 

I am pretty sure it is the A580 five-speed overdrive automatic in the 2012. RPM is important since a lot of driving is on the freeway up a pretty steep pass. There are a lot of trucks driving 40 everyone else is doing 70+...I would like to at least be going comfortably at 65. I have to drive it later in to the year since my daily driver doesn't have 4wd (a Camaro) and my driveway doesn't de-ice until March. My current 35s (General Grabbers) are 34" when measured. I definitely have upgraded driveshafts in the mix, maybe some JE Reel ones.

Thanks for the info.

 

Wow, that is pretty good. What year is your JK? Is it an auto?

 

I have 3.6 w 35's and 4:56 ...
Perfect ....