Checking Tire Pressure
| 01 March 2002
Correct tire pressure is important because it helps to maximize tire wear, it contributes to predictable handling and braking, and it contributes to ride comfort. Unless there is a specific reason to deviate, (towing or open-track, for example) follow the manufacturer’s inflation guide. If you check the pressure in the morning before the car is driven, you can be confident of a high degree of accuracy.
Pressure should be checked when all four tires are at the same temperature and, to comply with manufacturer’s recommendations, they should be cold. Cold means they should be at ambient temperature; i.e., they should not have been driven recently and they should not have been exposed to uneven heating while parked (space heaters in garages or direct sunlight are examples of uneven heating). Morning is one of the times when all four tires meet the temperature criteria. If your tires are exposed to uneven heating or morning is not a good time for you, you should devise a special set of circumstances to stabilize (ambient cold tire) temperature before checking pressure.
Check pressure at least once a month and don’t forget the spare tire. Note that seasonal temperature changes can cause the pressure to change several psi. Monthly checks will “catch” pressure changes related to climate as well as changes caused by such things as slow leaks. Check pressure with a good gauge, either pencil-type or round. Don’t rely on gauges attached to gas station air pumps; they can be very inaccurate. The pencil-type is usually a good choice because it is relatively inexpensive and quite accurate. If you want or need exceptional accuracy, get a round gauge but buy an expensive one because the inexpensive ones are usually not as accurate as a pencil gauge.
Adjust tire pressure as required by either adding or releasing air. If there is too much pressure, release enough air to bring the pressure to specification. Release air in small bursts and check the pressure after each release until the correct level is reached. If the pressure is low, add air as needed. If you have a compressor of your own, add enough air to bring the pressure to the correct setting and you’re done. If you need to get air from a gas station, the best accuracy is achieved by over-inflating the tires to a pressure 3 or 4 psi above the correct setting and then releasing enough air to meet the specification. Don’t release the air right away. Inflate the tires in the evening before the car is parked for the night and then release excess pressure in the morning to bring the psi to the correct setting. When you finish checking and adjusting pressure, install dust caps on the valve stems to keep dirt and moisture out of the valve.
When you check pressure, also take a minute to look at overall tire wear. If the wear indicators are flush with the rest of the tread, it’s time for new tires. When the front tires show an uneven wear pattern, its time for an alignment.