What Is a Tire Gauge? Definition, Meaning and Concept

A tire gauge measures the air pressure in any pneumatic (air-filled) wheel or tire. The results are usually read in PSI, pounds (of air) per square inch. Automotive tires have recommended PSI levels printed on the tire itself and listed on a chart inside the driver's side door panel. After reading a tire gauge, the PSI number is compared to the tire manufacturers recommended PSI and compressed air can be added until the ideal pressure is reached. Under-inflated tires can cause poor fuel efficiency and a higher chance of tire failure. Over-inflated tires can cause dangerous blowouts and noticeable loss of handling.

A commercial tire gauge comes in different forms. One of the most popular types resembles a pen, complete with a clip for shirt pockets. At one end of the tire gauge is a rounded tip with a small opening and a post in the center. This tip fits snugly over a standard tire inflation valve. As the user presses the tire gauge onto the valve, some air can escape from the tire. This shouldn't affect the actual reading much, but a good airtight seal is important.

At the other end of the pen-style tire gauge is a square opening that houses a plastic tube. On the side of this tube are calibration marks that denote pounds of air pressure. Air escaping from the tire valve forces the plastic tube out of the casing at a predetermined speed. Once the tube has stopped moving, the user can look at the last visible gauge mark to determine the current PSI level of the tire. If the gauge reads 25 PSI and the recommendation is 35 PSI, then ten 'pounds' of air should be added to the tire. An air compressor with an appropriate tire valve attachment can add extra pounds until the tire gauge reads 35 PSI.

Another type of tire gauge is attached to a commercial air compressor at service stations. Customers can check the PSI readings of each tire for free by connecting the compressor hose to each valve stem. A metal tube performs the same measurements as the plastic version, with a spring to return it to the casing between readings. If a tire is found to have low pressure, the customer can activate the coin-operated compressor and add more air. The attached tire gauge can be used at any time to measure the process.

Keeping tires properly inflated is something every driver can learn to do. It is especially important to check your tires before long trips and during extremely hot weather. Periodically check the air pressure of the spare tire and any other vehicle that uses pneumatic tires, such as a lawnmower or trailer.