There are many reasons why tire inflation is important. Even just a pound or two of under inflation in your tires can be a problem. Here's why:
Fuel Economy: Improper inflation of your tires can add rolling resistance, thus compromising your fuel economy. The loss of gas mileage means more fill-ups, and more fill-ups means more money out of your pocket.
Handling: Low tire pressure may cause poor handling and longer stopping distance. If you are a highway driver, this can be especially hazardous.
Tire Wear: Under inflated tires are under a lot of stress, especially the steel belts. When the steel belts have more pressure on them due to improper inflation, they become hot and are more likely to wear prematurely.
Studies have shown that proper inflation can give you as much as a 3.3 percent increase in fuel economy. It is important to remember that it is difficult to detect low tire pressure just by looking at them until they get really low (say 20 psi or so). At this point, it would be best to have your local tire shop or auto mechanic take a look at the tire to ensure the low pressure is not a faulty tire. As the temperature fluctuates, so will your tire pressure. When the air outside is colder, the air inside the tire shrinks, thus causing a lower pressure. As you drive, the air in the tires will heat and expand, hopefully to proper inflation. With newer vehicles, your PCM will most likely have a Low Tire PSI indicator light that will notify you when your tire pressure is low.
Whether your vehicle is equipped with an indicator light or not, we recommend that you check your tire pressure once a month to ensure proper inflation.