Check & Re-check
For the small amount of time it takes, checking tire inflation at least once a month is one of the best investments you can make to get the maximum life out of your tires.
• Proper inflation improves gas mileage by more than 3%, when maintained regularly.
• Under-inflated tires can lower gas mileage by 0.4 percent for every 1 psi (pounds per square inch) drop in pressure of all four tires. You may want to check your tires more often during the winter months. Tires will lose about 1 psi of pressure for every 10 degrees Fahrenheit of temperature drop.
• Keep an accurate tire pressure gauge in your car's glove box (many gauges at "air stations" give false pressure readings) and check the tire pressure when the tires are cold.
• While you're at it, don't forget to check the spare. There's nothing more annoying than a flat spare when you have a flat tire.
“Cold” Tires vs. “Warm” Tires
The recommended pressures are based on a “cold” reading, i.e. before they have been driven ANY distance. Once driven, the warm air in tires produces a higher PSI reading.
If you have been driving your vehicle and think that a tire is under inflated, fill it to the recommended cold inflation pressure. While your tire may still be slightly under inflated due to the extra pressure of a warm tire, it is safer to drive with air pressure that is slightly lower than the vehicle manufacturer's recommended cold inflation pressure than to drive with a significantly under inflated tire. Since this is a temporary fix, don't forget to recheck and adjust the tire's pressure when you can obtain a cold reading.
Here are some of the parts of a Dial Gauge