A tire gauge can be one of the best tools you have for saving money on gas. Underinflated tires produce drag, so your car has to work harder and burn more gas to maintain the same speed. So get out your gauge and check your tires every few weeks, and refill as necessary. Don't go by the pressure printed on the tire itself, though. Your car owner's manual should list the pressure you want. The Department of Transportation estimates that you can get up to a 3% improvement in fuel economy by keeping your tires properly pressurized, which adds up over time. Taking care of your tires also means they last longer, another area of savings.