How Often to Check Air Pressure

• Federal law began requiring a Tire Pressure Monitoring System (TPMS), an electronic system that displays real-time tire pressure readings, in all new cars as of September 2007. Even though some cars started using TPMS systems long before 2007, there are many vehicles still on the road needing to check the tire pressure the old-fashioned way.
  
  Looking at the tire isn't good enough. A tire that's high or low by 10 pounds of pressure per square inch may look normal, and radial tires often give the appearance of being low, especially on the front axle where they bear the weight of the engine.
  
  The best advice is to check your tire pressure once a month and before taking a long trip. Keeping your tires properly inflated increases their longevity and can help you save money on fuel.
  
  

Proper Tire Inflation and How to Check it

• Tire information placards that show the air pressure recommended by the manufacturer are standard on every vehicle. Most will have them located in the driver's side door jamb, but older models may have them in the glove box, passenger rear door jamb (of Ford sedans), under the center console or inside the gas hatch door. Keep a tire pressure gauge in the glove box, and refer to the tire information placard in order to properly adjust the air pressure.
  
  Unless the tires on the vehicle have been upgraded to specific performance tires, you should always abide by the air pressure recommended by the manufacturer and listed on the tire information placard. The sidewall of a tire will list the maximum tire pressure the tire can withstand, but a tire filled to maximum level does not allow for margin of variance.
  
  

The Elements and Tire Pressure

• Tire pressure rises in hot weather and falls in cold as the air expands and contracts. Because of this, your tire pressure will vary with the seasons and with the hotter and colder times of the day. Cars that are in storage or parked for long periods can lose a pound or two of air pressure per month. Tire temperature and air pressure will also rise while you are driving; this is why it's not a good idea to fill the tire up to maximum pressure listed on the sidewall.
  
  A puncture by a small foreign object will almost always cause a slow leak where the tire has to be filled repeatedly with air. A tire or tires that have to be filled frequently should be checked by a qualified tire technician for slow leaks, which can also be caused by faulty valve stems.