You can improve your gas mileage by up to 3.3 percent by keeping your tires at the recommended air pressure, the federal website FuelEconomy.gov says.
OK, the savings here aren't that big unless your tires are way underinflated. But you'll also be making your car safer and helping your tires last longer.
A technical note from the website: "The proper tire pressure for your vehicle is usually found on a sticker in the driver's side door jamb or the glove box and in your owner's manual. Do not use the maximum pressure printed on the tire's sidewall."