thymeclock is right, the tires affect it, the cold weather (winter blend gas?) affect it. it could also be the that your due for spark plugs. i replace mine every 25k miles. you might be due approaching 50k..

larger tires also most likely means more weight, it is also a final ratio change which means harder acceleration. if you stop and go a lot then you are using more gas to more a larger diameter tire that weighs more than oem. however on the highway you might 5-6% off so every 100 miles you go could actually be 106. with @ 350 miles to a tank, you might actually be traveling 371.


but like thymeclock said, there is a lot that goes into it.