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When tires are underinflated, heat builds up in them and can cause a blowout. (Photo by Phil Reed)
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Most gas stations have an air compressor (which the attendant will often turn on for free). Many compressor hoses have a built-in gauge so you can tell when you've filled the tire to approximately the right level. (Photo by Phil Reed)
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If you buy your own air compressor, you can more easily fill your tires at home. (Photo by Phil Reed)
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A digital tire gauge such as this one will only cost about $10 and is easy to use. The tire pressure, measured in psi (pounds per square inch), is shown in the clear plastic window. (Photo by Phil Reed)
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The recommended tire pressure specification is listed on this label which is usually found in the doorjamb on the driver side (or in the glovebox or listed in the owner's manual). This label tells you that the tires should be filled to 32 psi (pounds per square inch). (Photo by Phil Reed)
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How To
How To Check Tire Pressure and Inflate Tires
Drive Safely While Saving Money and Gas
By Philip Reed, Senior Consumer Advice Editor
Email
Click here to view video. 
Underinflated tires might cause an accident that could kill you. Need another reason for inflating your tires?
Underinflated tires increase tire wear, which could burn through a set of $400 tires a year early. Need another reason?
Underinflated tires waste gas. How much gas? The Department of Transportation estimates that 5 million gallons of fuel per day are wasted due to low tire pressure. That's more than 2 billion gallons per year, just because people don't take the time to inflate their tires properly.
OK, OK, you get the point. Inflating your tires to the specified pressure is important. So make it a habit to check and refill your tires once a month. And remember, you can't tell if a tire is underinflated just by looking at it. If it actually looks underinflated, it is way underinflated.
Checking Your Tire Pressure
Here's how to check the pressure in your tires with the least amount of muss and fuss.
- Buy a digital tire gauge and keep it in the car. (This will only set you back about $10.) Consider buying a small notebook that you can use to record your tire pressure and, later, your increased fuel economy.
- Find the tire pressure level required 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.
- Check the pressure when the tires are cold. Tires heat up as they drive. They take about a half hour to cool down. Or you can just check the tires first thing in the morning.
- Unscrew the valve cap and set it to the side or in a pocket where you won't lose it.
- 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.
- 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 get a portable air compressor. If you do this you can refill your tires at your house or in your garage. Some of these compressors are cheap and not really up to the task of quickly inflating your tires. Spend a few extra dollars to upgrade to a higher level compressor that connects to your battery terminals rather than running off the cigarette lighter.
Most people, however, will just refill their tires at the gas station. Even though many air compressors charge 50 cents, 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:
- Pull your car in close to the air compressor so the hose reaches all four tires.
- Turn on the air compressor. (You will hear the compressor motor beginning to run.)
- Remove the stem caps and set them to the side or in a pocket.
- 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.
- 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.
- Adjust the pressure in all the tires in the same way. (Note: If the tires are warmed up, inflate the tire pressure to 3 psi over the specified amount.)
- 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.
- Replace the valve caps on all the tires.
If you get in the habit of checking your tire pressure once a month, you will eventually find a good gas station that has a conveniently located air compressor.
Now it's time to enjoy improved fuel economy, reduced tire wear and — above all else — safe driving.
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