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

Underinflated tires might cause tire failure and an accident that could kill you. Need another reason for proper tire inflation?

Underinflation increases wear, which means you could burn through a $400 set of new tires a year early. Need another reason?

Underinflated tires waste gas. The Department of Transportation estimates that 5 million gallons of fuel a day are wasted due to low tire pressure. That's more than 2 billion gallons per year of gas wasted just because people don't take the time for the right tire inflation.

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You get the point. Inflating your tires to the specified pressure is important. So make it a habit to check and refill them 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, way underinflated. And you can't really rely on a tire pressure monitoring system (TPMS) to keep track. Most systems only warn you when the pressure is 25 percent below the manufacturer's recommended tire pressure.

Checking Your Tire Pressure

So it's on you. Here's how to check tire inflation pressure with the least amount of muss and fuss.

  1. Buy a digital tire gauge and keep it in the glovebox. (This will only set you back about $10.) Record the pressure and, later, your increased fuel economy in a notebook or in your smartphone.

  • Find the required pressure level. 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 front and the rear tires.

  • Check the pressure when the tires are cold; they heat up as you drive. They take about a half-hour to cool down. Or you can just check the tires first thing in the morning when the ambient temperature is lower.

  • 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 noting the pressure of the tires as you go around. You can refer to your notes 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, for 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.

    More pressure is not better, however. An overinflated tire is, in the words of the experts at Tire Rack, "stiff and unyielding," and its footprint on the road is smaller. They can be damaged more easily if they hit potholes or road debris.

    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. 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:

    1. Pull 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. It 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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