Checking your tires during the summer is especially important, so be sure to do a visual inspection every time you stop for gas. A bulging sidewall could mean the tire pressure is low. Tires that are underinflated have a higher rolling resistance, which decreases your vehicle’s efficiency, causing gas mileage to drop. By keeping your tires properly inflated, you can improve your gas mileage by as much as 3.3 percent. To find the proper tire pressure, check your vehicle owner's manual or the specification sticker on the door jamb. You may also consider replacing your tires with efficient "low rolling resistance" tires. Doing so could save up to 6 percent of gasoline use on certain vehicles. Go online to find out if your car is a good candidate for these tires.