Air Pressure & Inflation
Answers
  1. How much air should I put in my tires?
    You should follow the vehicle manufacturer recommendations for air pressure. These recommendations are shown on the vehicle placard on the driver door jamb and in the owners’ manual. The maximum air pressure label on the sidewall of the tire is not the recommended air pressure for your vehicle. Inflation pressure must be checked when the tires are “cold,” meaning without friction induced heat from driving. Heat build up is normal during operation and tires checked “hot” would give a misleadingly high pressure reading. Do not lower air pressure in a warm or hot tire. Allow at least two hours after driving before checking air pressure.
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  2. At what pressure is a tire considered under inflated?
    The tire industry considers a tire under inflated when it is 20 percent below the pressure recommended by the vehicle manufacturer. The recommended air pressure settings are shown on the vehicle placard (see question 9). It should be noted that the Tire Pressure Monitoring Systems (TPMS) by government mandate do not display a warning until a tire is 25 percent below the vehicle manufacturer recommended pressure. At this level the tire industry considers the tire to be severely under inflated. Therefore do not wait for a TPMS warning signal to check inflation pressure.
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  3. Why do my tires continue to lose air?
    A continuing loss of air in a single tire usually indicates a problem with that particular tire. Have that tire checked for punctures, defective valve assembly, or lack of proper seal between the rim and tire. A slow seepage of all tires of one to two pounds per month is fairly common. A rubber tire, unlike a metal container, is not air tight and is subject to gradual movement of internal air pressure through the casing.
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  4. often should I check the pressure in my tires?
    This varies and is dependent on the ability of your tires to retain air pressure. One vehicle may maintain adequate pressure between 5000 mile rotation intervals while another may require air every 60 days. Under inflation that occurs in 30 days or less is abnormal and is cause for having the tires inspected. It should also be noted that a tire “loses” one pound of air pressure for each ten degree reduction in ambient temperature. This necessitates air pressure adjustment when moving into winter weather.
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  5. Will my Tire Pressure Monitoring System work properly if I change my truck tires from P-Metric rating to Light Truck Load Range?
    No it will not work properly and Active Sensor TPMS will probably be damaged by the higher pressures that light truck tires require. TPMS installed by a vehicle manufacturer are set in accordance with the recommended inflation levels for a particular vehicle. These systems are preset and the warning levels are non-adjustable. Furthermore Active Sensor Passenger load range models embody a maximum pressure level that may be below the pressure used in a light truck tire. Tire pressures that exceed the maximum pressure will damage the sensors and necessitate sensor replacement. These issues also may prohibit moving wheels with active sensor systems from one vehicle to another.
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  6. What is Nitrogen Inflation and is it beneficial?
    Nitrogen Inflation, as the term suggests, substitutes a near 100 percent nitrogen gas to inflate tires rather than normal atmospheric “air.” Nitrogen is commonly used in commercial and military aircraft and high-speed racing tires. Nitrogen inflation for consumer tires became available with the development of a filter membrane material to eliminate most oxygen from atmospheric air. There are two benefits of nitrogen inflation. The first is that nitrogen will not support moisture like atmospheric air. This makes the compressed gas more stable over wide variations in operating temperature. The second advantage is that a molecule of nitrogen is larger than a molecule of oxygen. This makes air retention slightly better for nitrogen. The disadvantage has to do with the need to maintain 96 percent or higher concentrations of nitrogen to have any benefit at all. Poorly maintained filter membrane units, normal air trapped in the tire during mounting, and adding atmospheric air all negate the benefits of nitrogen inflation. Central Tire uses a refrigerating compressed air dryer to eliminate moisture in its compressed air. Rubber company studies show this to be as effective for moisture reduction as nitrogen inflation. While nitrogen slows the migration of compressed gas through the tire casing, it does not eliminate seepage and the need for adding nitrogen over the life of the tire. Therefore tires inflated with nitrogen can only have nitrogen added to retain the benefits. Central Tire considers nitrogen to be more of a “marketing ploy” than a true benefit.
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