What Every Driver Should Know About Tire Pressure Monitoring Systems

What Every Driver Should Know About Tire Pressure Monitoring Systems      

       The United States government has passed legislation that requires all new passenger vehicles (beginning with 2007 model year vehicles) to be equipped with tire pressure monitoring systems.  

      Maintaining the correct tire pressure for a vehicle is the variable in how much load its tires can safely carry. The correct pressure will carry the weight without a problem. Too little tire pressure will eventually cause catastrophic tire failure.       

         Tires aren't invincible. They are made of individual layers of fabric and steel encased in rubber. If a tire is allowed to run low on air pressure, the rubber is forced to stretch beyond the elastic limits of the fabric and steel reinforcing cords. When this happens, the bond between the various materials can weaken. If this is allowed to continue, it will eventually break the bonds between the various materials and cause the tire to fail. Even if the weakened tire doesn't fail immediately,  it won't heal after being reinflated to the proper pressure. So if a tire has been allowed to run nearly flat for a period of time, the tire should be replaced, not simply repaired or reinflated.       

          Studies have shown that running tires with too little air pressure is not uncommon. It's been estimated that about one out of every four vehicles on the road is running on underinflated tires. This also means that one out of every four drivers is needlessly sacrificing their vehicle's fuel economy and handling, and reducing their tires' durability and tread life.   

       This has made tire pressure maintenance an important safety issue throughout the automotive industry. The U.S. government has passed legislation that requires all 2007+ model year passenger cars and light trucks under 10,000 pounds of gross vehicle weight to be equipped with tire pressure monitoring systems. The main purpose of these systems is to warn the driver if their tires are losing air pressure, leaving the tires underinflated and dangerous. The National Highway Traffic Safety Administration (NHTSA) provides vehicle manufacturers two options to comply with the law. The first is to install a direct tire pressure monitoring system that warns drivers when the air pressure in any of their tires drops at least 25% below the recommended cold tire inflation pressure identified on the vehicle placard or owner's manual. The second is to install an indirect tire pressure monitoring system that would warn the driver when a single tire has lost at least 30% of its inflation pressure compared to the other tires on the vehicle. The two systems have different warning thresholds because the indirect systems cannot offer the same information or accuracy of the direct systems.           What’s the difference?

         Because direct systems have a sensor in each wheel, they tend to generate more accurate warnings and can alert the driver instantly if the pressure in any one tire falls below a predetermined level due to rapid air loss caused by a puncture. In addition, a gradual air loss over time will result in too little air pressure being detected. Many direct systems use dashboard displays that provide the ability to check current tire pressures from the driver's seat.
       Direct systems attach a pressure sensor/transmitter to the vehicle's wheel inside the tire's air chamber. Most Original Equipment systems attach their air pressure sensor/transmitter to a special tire valve that clamps through the wheel. Since snap-in rubber valves are used for most wheels that aren't monitored by a direct system, the presence of a metal clamp-in valve typically identifies the presence of a direct tire pressure monitoring system. The transmitter's signal is broadcast to the in-car receiver and the information is displayed to the driver.      

       If your vehicle is equipped with the direct system you must be aware that outside temperature will effect this. As temperatures drop the tire pressure will drop also; for example, if you set your tire pressures at 32 psi and the tire temperatures are at 70 deg F, for every 10 degree drop in tire temperature you will loose 1 PSI. So if your tire pressures were set at 32 PSI at 70 degree temperature and you parked your vehicle outside and the temperature drops to 20 degrees, your tire pressures will now be 27 PSI . This will cause your Tire Pressure Warning Light to illuminate  until you drive the vehicle awhile and heat up the tires. So during winter months it is recommended to inflate your tire pressures to the upper limits. Indirect Systems are not effected by this. However Indirect Systems can generate false warnings. For example if your wheels spin on ice or snow this could cause the light to illuminate, or if you are driving around a long slow curve that causes the outside tires to rotate faster than the inside tires this could also illuminate the warning light.    

   It is recommended that you check your tire pressures once a month.