I went from stock sahara duelers to 33's with a 2" lift and lost about 3.5mpg. I did the calculation by hand based based on the gallons used and current odometer miles traveled reading but that would now be a bit off based on the jump in tire size.

Time to get a procal.

 

I think they were 225 something 16 Goodyear wrangler. Now I have nitto trail grapplers 285 65 18

 

I'm new to the jeep forums so I'm unfamiliar with some of the lingo. What would a procal do? I'm assuming it's a computer reprogramer.

 

Yup it is, allows you to reconfig your computer for proper readings for increased tire size, gear change, lift, fuel and tire pressure! The BOMB! must get

 

it is made by aev u can pick one up on most 4x4 online stores

 

you can also just do manual calcs. take the mpg you calc on a tank and multipy it by the new larger tire diameter divided by the old smaller tire diameter. with the larger tires you're going more miles than your odometer reads so your mpg is better than what you think it is.

 

Even though the computer is reading a lot less? I know changing gears makes a big difference on the spedo, I didn't think it would be that big of difference on my fuel. I have to just fill the tank and clock the miles to calculate myself. What's the difference in those programmers. I know there are different ones so is procal the best? I do see a lot of others for sale on te billboard.

 

Stock tires on my 2010 Rubicon

First year overall: 17.24
First 9 months of second year: 19.24

I keep track of each tank incase I have a sudden drop. I had a large drop on a vehicle years ago and the dealer didn't want to take my word for it. I now keep track of each tank and the driving conditions for it.

 

i'm not saying not to get a procal, you should to correct both your odometer reading and your evic mpg on the display.

but to correct your mpg with the new tires vs the old tires you just have to do the manual calc and tire diameter ratio. if you've done other things like changing gears the same thing applies, multipy by the new gear ratio divided by the original gear ratio.

your odometer and evic only count the number of revolutions to determine miles and mpg. for one revolution with the big tires you're going a longer distance than with the small tires.