You can improve your gas mileage by up to 3.3% by keeping your tires inflated to the proper pressure. Under-inflation increases tire wear, reduces your fuel economy, and leads to higher carbon pollution emissions. Properly inflated tires are safer and last longer.
Check your tire pressure regularly. If you don’t know the correct tire pressure for your vehicle, you can find it listed on the door to your vehicle’s glove compartment, or on the driver's-side door pillar. Do not use the maximum pressure printed on the tire's sidewall. When it’s time for new tires, consider purchasing tires with "low rolling resistance," an energy-saving feature.
Learn more tips to improve your fuel economy: http://www.fueleconomy.gov/feg/driveHabits.jsp