YeA we all know how you feel. So here's tp things other than a tune up that'll help a lil. First if you've never changed the o2 sensor and you have over 90k miles chNged the front sensor, the one front of the cat. Second click the link on my sig and do a full seafoam treatment. That'll help big time. There is also regearing to 4.10 to that can help and yea I said 2 things but last even tore pressure make a diff. Check the pressure and for 31s you can be around 31-32 psi

 

remember that they are not correct mileage wise vs stock tires. the circumference of a 31" is more than that of the stock 225/75R15. was looking at my mileage and almost had a heart attack until i thought about the fact that 33s are 16% taller

 

How exactly do you compensate the larger tires on top your trip meter to get a more accurate idea of your mileage per tank. If that makes any sense.

Like, If im getting 300 kilometers on a tank with 32's, how many kilometers am I actually going?

 

Ya I should adlest be geting 16 miles to the gallon
And I've been told my gearing is 4.10
I'm going to try the seafoam in the next couple of days
Ya I'll see what happens and hope it helps haha

 

remember pi from school? i thought about working it out one day and then stopped caring that much. i would just go off of percent and hope its close

 

All I do is set my trip and drive a full take then take the gallon the tank is and divide it and I get my gas milage

 

Your get 15 miles to the gallon

 

so quick break down to work it out since people are asking

200 miles on your stock setting odo for a jeep that came stock with 225/75R15 (28.29") after installing 285/75R16 (32.83") and used 12 gallons

32.83*pi=103" for a full revolution
28.29*pi=88.83" for a full revolution
63360" in a mile
63360*200=12672000 inches in 200miles
12672000/88.83=142654 revolutions of the tire in 200 miles
142654*103=14693414" actual inches traveled by a 285/75
4693414/63360=232 miles traveled
232/12=19MPG

 

That makes since

 

Killer, thanks for the formula. I like to keep track of my mileage and I wasn't sure how to do it with 31s bc they make the odometer show less miles than actually traveled which would destroy the gas mileage result using the standard formula. Am I right?

I will put your formula on a card and laminate it and put it in my visor for quick reference.

 

well it wont be as good as what the real gas mileage is