We thought, if anything, our mileage should go up from putting on tires with a smaller contact patch that were slightly taller for lower highway rpms, and an axleshaft that wasn't bent. Instead, over the next 600 miles, our mileage went from a 17-18 mpg on the highway to 13 or 14 mpg. Then one day we fired it up and the accessory belt was squealing. The power steering pump had died. We mangled the pulley trying to get it off and replaced it with this one from Gen-Right Off Road since the dealer was back-ordered, and the pulley cost less than a decent puller. After we put the new pump in, our mileage was back up in the 17-18 mpg range. The failing power steering pump significantly affected our mpg.