I have a 2014 rubicon X unlimited with 4.10 gears and a auto, I just installed a rubicon express 2.5" lift and want to do wheels and tires next, I would like 35's but I don't want to kill the mileage, right now I get 17 MPG on the high way, my 2013 got 20 on the highway with 3.26 gears. Maybe you guys can let me know what size tires and gears you have and what the MPG is. Also has anyone got better MPG by going to a larger tire with the 4.10 gears due to lower RPM on the highway. Sounds like a dumb question but my RPM at 70 MPH is about 800-1000 rpm higher with the 4.10's vs the 3.26's. Any help will be greatly appreciated and sorry if this may be a repeat forum.

 

It does sound weird to have higher rpm's with bigger wheels. I'm thinking you must have an automatic transmission and your engine is having to work harder to maintain that kind of speed due to wind resistance, being higher off the ground & moving more mass. The extra RPM's are being lost in the torque converter as heat.

 

I haven't installed the larger tires yet, the comparison is between my 2013 and my 2014 rubicon which runs a higher rpm at highway speed, there is no transmission slippage. What I'm trying to find out is if anyone got better highway fuel economy on a rubicon with 4.10 gears after installing larger tires (33" or 35") due to the larger tire diameter lowering the RPM at highway speed. I know its a weird question, with larger heavier tires you would expect there to be more load on the engine but the RPM is going to lower. Im think of 33" tires which should be only 1 " larger.

 

You will not get better gas mileage. Bigger heavier tires are going to get you worse mpg's. Proper gearing will minimize the loss.

 

I have a 2014 JKUR with 4.10 gears and a slush box, on 35's with a 4" lift and my mileage definitely got worse. I installed a Flashpaq later and use the economy tune, and now get 17 mpg on the highway, if the terrain is reasonably flat. But mixed town and freeway driving nets me about 14 to 15.

 

17 MPG doesn't sound too bad considering thats what I'm getting now with stock tires, I don't think the Jeep is broke in yet though, I know on my 2013 it seemed like it took about 10 to 12K miles to fully break in.

 

After my change to 35's the best I got so far has been 17. However I only have 1500 miles on my rubi x with a 6 spd. I just recently added the flashpak and have it set at the 91 tune. I have not run thru a full tank yet though. I do not drive many miles during the week. Probably only 25 total because I commute in a different vehicle


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I'm pretty happy with 17. If its gets better, bonus. Would like my mixed mileage to be better, but whatever. Considering that its a 6 banger driving ~5000 lbs, I can't really bitch.