How to measure tire pressure

Rubber is a porous substance, and tires will inevitably lose some air over time due to seepage. Tire pressure is something that’s neglected by many drivers, as an “out of sight – out of mind” sort of condition. Low tire pressure, however, costs money in terms of increased rolling resistance and poorer gas mileage. Tires that are habitually run low on air also wear out prematurely, due to heat buildup and an uneven wear pattern.

The good news is that it’s easy to check pressure with a tire pressure gauge, and if you do end up with low air, it's an easy problem to fix.

For 100 years, tires have used the same valve design (known as a Schrade valve), identical to the valves on bicycle tires. They’re still the same design because the Schrade valve does its job well and there has never been a need to improve on it. 

• Don’t rely on the tire pressure gauge built into the air hose at the gas station – they are not very reliable for an accurate reading.
• Pencil-style gauges have long been the standard – they’re cheap and reliable. Newer tire gauges use a dial-type reading or even a digital readout for a slight improvement in accuracy.
• Make sure that the gauge is seated firmly on the Schrade valve, and is depressing the spring-loaded stem at the valve’s center. Don’t be afraid to put some pressure on it – anything less won’t give you an accurate reading.
• Remember that modern radial tires won’t “look” low until they are drastically low on pressure – a tire can be 12 to 15 lbs low on pressure without deformation of the sidewall.
• You can find recommended tire pressures stamped on the tire’s sidewall. Add air and check regularly. If you over-inflate, most pencil-style gauges have a pin on the back of the gauge head that will allow you to depress the spring-loaded stem on the tire valve and bleed off excess air pressure.