hi guys, I recently went to Cooper STT 315x75x16 tires on my JKU with auto transmission.
it has 3.73 gears due to the max towing package, it has no problems on the highway with power, may have lost 2 or 3% but not enough to even consider a regear job.
what has been your experience when going to large tires?

 

I run 3.73s w/ 35s and it's completely fine. That is, until I get behind the wheel of my wife's stock 2 door with 3.73s then I realize what I'm missing.

But it's really not a fair comparison since I have 2 more doors and an extra ~600# in armor.

 

I'm currently running the same tires, stt 315, and 3.73 gears. I'm on a 6 speed manual though, I would say I noticed a slight decrease in power gains from stock, but I did also use a super chips flashpaq and programmed to the 91 performance, definitely helped make up some of that lost power and also the peace of mind that my speedo was on target.

However at some point im planning to regear to either 4.88s or 5.13s, thinking at some point down the road I may go to 37s, but not for a while.

 

Glad to hear when upgrading to 35's and having 3.73 gears the power decrease is not that bad. This is probably the route I will have to take for several months before re-gearing.

 

Great news OP! Any issues with shifting - auto tranny holding gear or short shifting? I take it that you do not have a programmer. Please let us know your thoughts after some more miles. I'll be purchasing a 2015 JKUS in July and have been researching upgrades/issues.

 

I've been running 35s with 3.73s on my 2 door auto for a year now. It is definitely manageable in the flatlands (I live in FL). My wife's 2012 4 door is noticeably peppier than mine with her nearly stock setup and 3.73s. I went wheeling up in WV though and that's where the poor gearing had a major affect, driving through the mountains. Long inclines the Jeep wouldn't shift into a higher gear unless I mashed the skinny pedal to the floor. I didn't like it at all. So in the flatlands I'd say you're okay if you don't mind the small performance drop but in hill country it will surely get old fast.

My Jeep is going in the shop on Monday for 4.56s.

 

I ran 35's and 3.73 for almost 2 years. I turned off OD as soon as I started up! It was ok for where I live. But, went to 5.13 and TT's front and rear! Does not take as much pedal to get moving and jeep computer say 1 mpg better.

 

Some are fine with that, some are not. Depends on driver preference. It seems those with the 3.6 find it more tolerable than those with the 3.8.

 

I noticed this morning when driving on the hwy that my '15 JK unlimited w the 3.73's and 35's really doesn't like 6th gear that much when going up hills. The computer is showing a decrease from around 17mpg down to about 14mpg. I guess 5th gear is gonna be my new friend lol

 

I had 3.73 and 35s on a manual and I personally thought it brought the suck. I never really thought much about acceleration - it's a Jeep. What brought the suck was highway driving. It just didn't like 6th gear and I spent way too much time rowing between 5th and 6th. I recall a 10 hour trip from MD to IL with lots of rolling hills. No joke, I shifted so many times that I had a sore hip for a week, and I'm a fit guy.

I went to 4.88s on 37s and it was awesome on the highway. No more shifting into 5th. Brought the enjoyment back.

Oh, and my MPGs actually went up when I went to 37s and 4.88. There is a lot to be said about operating the engine in an efficient range.