How to put air in tires

Fill your tires to the number on the door sticker, measured cold, once a month, and never to the number on the tire.

A person crouched beside a car, filling a front tire with an air hose and gauge from a portable air tank — Photo: Andrea Piacquadio / Pexels

Area: HandsFrom age 16Time to learn: 15 minutes

Check tire pressure with a gauge when the tires are cold, add air in short bursts until each tire matches the placard on the driver's door, and recheck.

SafetyPark clear of traffic and set the parking brake before kneeling beside a tire.

Why it matters

Underinflated tires flex more, run hotter and wear out faster. In NHTSA crash data, tires underinflated by 25 percent or more were 3 times as likely to be cited as the critical event before a crash. Correct pressure also saves fuel: the US Department of Energy says mileage drops about 0.2 percent for every 1 psi drop in the average pressure of all four tires.

In NHTSA's study of crashes from 2005 to 2007, tires underinflated by 25 percent or more were 3 times as likely as correctly inflated tires to be cited as the critical event in the moments before a crash.

Source: National Highway Traffic Safety Administration, Tire-Related Factors in the Pre-Crash Phase (DOT HS 811 617), 2012.Measured

How to do it

Find your number. Open the driver's door and read the tire placard on the door jamb, or check the glove box door or the owner's manual. It lists the cold pressure in psi (and often kPa), sometimes different for front and rear.
Ignore the number molded into the tire's sidewall. That is the tire's maximum pressure, not the right pressure for your car.
Check when the tires are cold: after the car has been parked for at least 3 hours, or has been driven less than a mile.
Unscrew the valve cap. Press the gauge straight and firmly onto the valve stem until the hissing stops, then read it.
To add air, press the air hose chuck straight onto the valve and fill in short bursts, checking with your gauge between bursts. If the machine lets you set a pressure, enter the placard number.
If you go over, press the small pin in the center of the valve for a second at a time to let air out, then check again.
Do all four tires and the spare, then screw the caps back on. A narrow temporary spare, called a T-type spare, needs 60 psi (420 kPa), far more than the other tires. Add air to it in small amounts, because its pressure changes quickly.
Repeat at least once a month and before long trips, heavy loads or towing. Expect lower readings in cold weather: pressure changes about 1 to 2 psi for every 10°F change in temperature.
If the tire pressure warning light comes on, check every tire with a gauge as soon as you can safely stop. The system warns only when a tire is about 25 percent low, which may already be too late to prevent damage, so it does not replace monthly checks.

Common mistakes

Filling to the maximum pressure printed on the sidewall instead of the placard number.
Relying on the dashboard light instead of a gauge.
Letting air out of tires that are warm from driving to match the placard. Warm tires read high, so they end up underinflated once they cool.
Forgetting the spare, which is often flat when you finally need it.

You can do this when …you can find your car's placard pressure, measure all four tires cold with your own gauge, and bring each one to that number.