Recently purchased 01 Frontier XE 4x4. Really a nice truck. Learned that it came from the dearler with 265/75R15s which are supposedly the equal to the 31/10.5R15(LT) that are on it. I'm not a proponant of oversize tires (more into fuel economy etc). Checked the first tank full as was only getting +/- 14 MPG. IS this normal or main due to the tire size. Plan on changing out the plugs, air & fuel filter etc and take it in for a tune. Input...?