Keeping a proper tire inflation pressure is a goal for every driver. When the proper air pressure is set, tire efficiency , fuel economy and durability are all maximized. Air in tires and supports car loads so depending on the specific load, the inflation pressure should be set accordingly.
For example, if a loaded tire is carrying 6,000 pounds when on the steer position, then the recommended tire inflation is 110 PSI for the common 295/75R22.5 low profile tire size. Load inflation manual describes the designed tire pressure made for given tire loads. These manuals can be found on each tire companies’ websites.
However, care must be exercised when reading these charts, since the recommended pressures have variance depending on whether the tires are being run as singles or duals.
Since it is totally difficult to change tire pressures every time the vehicle load changes, the recommended tire pressure at all times must be based on the worst case load scenario. Even if the average load may be significantly lower than the worst case load, it still is very recommended to set the pressure based on that worst case load scenario.
Load carrying vehicle drivers are typically worried about the frequency they should be checking tire pressures—and why tires lose so much air during the course of the year. Below are four reasons why tires lose air:
- Gradual loss of air through the tire casing can result in a loss of 1 to 3 PSI per month, depending on the particular tire make and model. The chemical component of the manufacture of the tire can play a big role on this osmosis of air. The make and gauge of the tire innerliner compound also plays a significant role in osmosis. Losing 2 PSI per month does not seem like very much, but after 12 months the whole tire would be considered “flat” and should be removed from service. If a tire is found to be 20% under the fleet’s specification, the recommendation is to remove the tire from use, dismount and check exactly what is going on with the tire.
- Slow leaking punctures or wounds in the tread are the major causes of tires losing air. A nail embedded in a tire’s groove may lead to a loss of 2 or 3 PSI per day, not 2 or 3 PSI per month as with osmosis. It is possible to check the tire pressure before the vehicle leaves in the morning, yet pick up a nail just a few minutes later.
- Leaking valve stems and cores are another cause of low tire pressure. Over-tightening valve cores can result in loss of air. There actually is a specification of 4 inches per pound of torque on a tire valve core. Valve core pre-set torque wrenches are available through tire supply companies.
- lastly , tires lose air during impact breaks. Running over large objects and hitting the curbs on those turns can lead to air loss, which is usually sudden and can result in an emergency roadside service call.
So, the frequency of pressure check depends on the type of service used. If cars use a high volume of mixed service and are on unpaved roads, then tires need to be checked a lot more frequently than tires running on vehicles that are going coast-to-coast over the interstates.
If the cars are coming back home every night and travel on good roads, then a good once a week check of tire pressures is the standard recommendation. However, it always is a good practice to check tire pressures as often as possible
Note: Always use a pressure gauge that has been calibrated. Some stick gauges are adjustable by turning a screw located in the bottom of the gauge. Many truck stops have air inflation calibration stations to check your pressure gauges. Even brand new pressure gauges out of the box are only accurate to +/- 3 PSI, so it is a good idea to check your gauges for accuracy on a regular basis.