Over-inflate your tires
False. Inflating your tires beyond the recommended level will reduce the portion of the tire in contact with the road and the resistance between the tires and the road, but over-inflating them can make for a rocky ride. Popular Mechanics has also road tested this theory and concluded that the gas mileage doesn't improve.
The difference occurs when under-inflated tires are pumped to proper levels. In fact, the Department of Energy estimates that this simple fill up can improve your gas mileage by 3.3 percent.