Hey guys. I'm pretty new to the forum, really appreciate all the info and advice you guys give..has already helped me out.

Anyway, I have a 2012 jku with 3.73s that I just put 35 nitto trail grapplers on. I do a lot of highway driving when I'm on the pavement, and I've seen my mpg's get killed by these new tires. Getting around 12-13 mpg. I really don't care about gas mileage, but I do worry that I'm rarely in O/D (5th gear) when on the highway. Obviously, that's what killing my mpg, I just want to know if this is bad for my jeep.

Even at 80 mph, I have to manually shift into 5th, and as I do I lose all power. Just pushing on the gas pedal lightly, it shifts down to 4th.

I realize I probably have to re-gear to solve this problem. Also, I have used the AEV procal...didn't really help.

To be more specific:

Is it bad for the jeep to stay in 4th at 75-80 mph?

Is there anything else I can do to help in some way...other then regear?

Someone help a new jeeper out please!

 

You really don't want it in overdrive with those tires. That motor is more efficient at higher rpms. Beung

 

Oops being that there isn't a tuner available for the 11's and 12's yet, a procal can help correct your shift points and calibrate the speedometer

 

Not a problem running at the higher rpms, although gears would get you back regular use of OD. I would opt for 4.56s, but here's a look at the gear chart from the FAQ which will help you make a decision. Also, slow down. More than anything, that's what's killing your fuel milage. It takes twice as much power to drive 80mph as it does 60mph. At 80mph over 85% of your power is used to combat aero drag and that isn't going to be changed by new gears. Slowing down is always the best answer for better efficiency, although putting an end to gear hunting will help as well.

Anyway, here's the chart from the FAQ,

 

You're just driving too fast.

Also, make sure you have your Pro-Cal set to the actual height of the tires. Measure them mounted on the JK - don't just set it on "35."