Maintaining proper air pressure in your car's tires may be the cheapest thing you can do to prolong their life and ensure the car delivers the best gas mileage it can. Since tire air pressure affects the way your car handles, it's an important safety factor, too. But what's proper air pressure?
There's no shortage of advice on how much pressure (measured in pounds per square inch) a car's tires should hold. Most motorists get two figures: one from the tire manufacturer molded into the tire sidewall, the other supplied by the car manufacturer, usually on a sticker in the glove box and always in the owner's manual. They're almost never the same.
The best course usually is to go with the car maker's recommendation. This figure, commonly in the 20-odd psi range, tends to be a compromise between maximizing ride quality (which many people find better at lower pressure) and tire wear (which higher pressure tends to minimize). It is within the range for tire safety and helps maintain the car's handling characteristics.
The inflation pressure figure molded into the tire wall (commonly in the 30-odd psi range) is the maximum recommended pressure. While this higher pressure tends to minimize wear, many people find it contributes to a harsher ride. The maximum pressure recommendation should not be exceeded. Some motorists choose a figure between the car maker's recommendation and the maximum allowable pressure. In any case, tires on the same axle should be inflated to the same pressure.
Tires commonly lose small amounts of air over time, so you should check the pressure regularly, perhaps once a month. With modern tires, eyeballing sidewall bulge is not an accurate way of doing this. Pressure should be checked with a pressure gauge when the tires are cold (a mile or so of driving is OK). Don't trust the gauges built into gas station air hoses. It's best to buy yourself a high quality gauge and replace it every couple of years.
This article was first published in January 1996. Some facts may have aged gracelessly. Please call ahead to verify information.