Check Your Tires Monthly
How do you determine the correct tire pressure for your car's tires?
Many people check the pressure listed on the side of their tires, but that's actually the wrong place to look. The number on the tire is the maximum allowable air pressure — not the recommended pressure for that tire when used on your vehicle.
The vehicle's recommended tire pressure is most likely lower than the maximum tire pressure. Find the proper inflation number in the owner's manual, on the driver's door pillar, the glove compartment door, or sometimes on the gas filler door.

Once you know the vehicle manufacturer's recommended tire pressure, you need an accurate tire gauge to check the tire pressure. Some tire gauges, such as the popular pencil-style gauge, are notoriously inaccurate. Analog, dial-type gauges or digital gauges tend to be fairly accurate.
Check tires when they are cold, meaning they are at air temperature. You can check tire pressure any time of the day, as long as the tires have been sitting for a few hours or haven't been driven for more than a few miles. Don't try to pull off the highway after driving for an hour and expect to get an accurate reading.
When you do check your tire pressure, remember to check all four tires. Just because three of your tires are at 30 pounds doesn't mean that the fourth tire isn't nearly flat. Finally, check the spare tire at least once in a while — it would be an unpleasant surprise to find it flat when you need it. If you have a small, space-saver spare, then the pressure for that tire is probably not the same pressure as your regular tires. The correct tire pressure should be printed right on this particular type of spare.
Stop by the Environmental Health Department (2nd floor of City Hall) to pick up a free dial style tire gauge. (While supplies last.)