How To Check Your Car's Tire Pressure and Inflate Tires

Underinflated tires increase tire wear, reduce fuel economy and can potentially cause a blowout.

Inflating your car's tires to the specified pressure is important. But simply looking at the tire and checking the information on the sidewalls is the wrong way to do it. If the tire looks slightly under inflated, chances are the pressure is way below the recommendation. Make it a habit to check and refill your tires at least once a month. Here's how.

Checking Your Tire Pressure
Here's how to check the pressure in your car's tires with the least amount of muss and fuss. You'll need a tire pressure gauge. These are available at auto part stores and cost about $10.

1. Find the tire pressure level recommended for your car. This information is usually on a yellow sticker in the doorjamb on the driver side (and it is also contained in the owner's manual). It might call for different pressure levels for the back tires and the front tires or different pressures depending on the load or use of the vehicle.

2. Check the pressure when the tires are cold, as this is how the automakers list these recommended tire pressures. Tires heat up as you drive, so measuring them while they are hot will give you an inaccurate (overly high) reading. They take about a half hour to cool down. You also can just check the tires first thing in the morning.

3. Unscrew the valve cap and set it to the side or in a pocket where you won't lose it.

4. Press the tire gauge onto the valve stem. There might be a slight hiss as you press down on the valve stem and again as you release it. You only need to do this for a second or two, long enough to get an accurate reading.

5. Read the tire pressure on the digital gauge. You might consider writing down the pressure of the tires as you go around the car. You can refer to this when you fill up the tires.

Now you can compare the tire pressure readings you got with the specified amount called for by the manufacturer (on the doorjamb or in the manual). If the level of pressure in your tires is below the specified amount, you need to fill the tires with air.

For example, the sticker on the doorjamb may say that the recommended level is 32 psi (pounds per square inch). When you check your tire you find it is 29 psi. You need to bring your tire pressure up to spec. It's estimated that for every 3 psi below spec, you burn 1 percent more fuel (and add 10 percent more tire wear). It's not uncommon to be 10 psi below spec, which would waste 3 percent more fuel and increase tire wear by 45 percent.

Filling Your Tires
There are at least two ways to refill your tires to bring them up to specification. You can go to an auto parts store and buy a portable air compressor. If you do this you can refill your tires at your house or in your garage.

Most people, however, will just refill their tires at a gas station. Even though many stations charge 75 cents to use their air compressors, you can usually get the attendant to turn on the machine for free.

Adjusting Your Tire Pressure
Here are the steps needed to adjust the pressure in your tires:

1. Pull your car in close to the air compressor so the hose reaches all four tires.
2. Remove the valve stem caps and set them to the side or in a pocket.
3. Insert coins or if the gas station attendant turned it on, you will hear the compressor motor beginning to run.
4. Press the hose fitting down on the valve stem and press the lever. You should feel air flowing through the hose and hear it inflating the tire. This can take a little effort to hold the hose on the valve stem.
5. Check to see when you have enough air pressure in the tires by releasing the inflation lever. The gauge on the hose fitting will show if you have approximately enough air pressure. You can check it again later with your own gauge. At this point, it is better to slightly overinflate the tire.
6. Adjust the pressure in all the tires in the same way. (Note: If the tires are warmed up, you can inflate the tire pressure to 3 psi over the specified amount as a general rule of thumb, but you'd still want to officially check the tires later.)
7. Recheck the tire pressure with the digital gauge. If the pressure is too high, press the gauge down just far enough to release some air from the tire. Check it again.
8. Replace the valve caps on all the tires.

Now it's time to enjoy improved fuel economy, reduced tire wear and (above all else) safe driving.