I'm ran some 31-9.5-15 and was getting around 15mpg, then i went to stockers and was getting around 16-17mpg, and then i aquired a set of 33-12.5-15 and i get around 14-15mpg. I'm running 3.73 on DD. As far as running with the top down, Its about equal for me A/C vs Top down I figure the air drag vs hp lost to A/C is about the same. I run around 70-75 driving to the coast ~35 miles with a 20 mph head wind everyday. My 33's I only drive around 65 or so because they were free and dry rotten. So I don't really wanna roll the heep. Oh yea Its a 2.4l with 6-spd. I have found that my CB is the best MPG mod I have done ever. I just draft and talk to truckers they usually don't care too much. I got the idea when i helped move my sister one year from Midland, Tx to Temple, Tx about 400 miles. I had to drive there first from Houston which is like 600 miles I think. Me and a buddy drove up and she rented a budget truck, I had my friend drive the jeep behind the truck as close as he could. getting 30 MPG. No S@#@.