Did you know that driving on underinflated tires is a big risk to your safety? Tires with the incorrect air pressure can cause instability, unsafe braking and cornering, and even tire failure.

Underinflated tires also take a toll on your wallet by worsening your gas mileage. Plus, driving on tires with low pressure wears them down faster, so you might burn through your set much sooner than you should.

Tires lose an average of about 1 pound per inch (PSI) every month. Even though it’s easy to forget about tire maintenance, refilling your tires is every bit as important as refilling your gas tank.

That’s why it’s important to check your tire pressure on a regular basis. Check Your Tire Pressure Day serves as an annual reminder that monitoring the air pressure inside your tires is a great way to prevent safety risks—and save yourself money!

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What Is Cold Inflation Pressure?

The term “cold inflation pressure” denotes the air pressure inside tires before a car has been driven. Driving on a set of tires warms them, causing the air inside to expand and the air pressure to increase. You should check your tire pressure while your tires are still cold.

First thing in the morning is best, or at least two hours after you have driven your car, according to the Tire Industry Association. If you check your tire pressure too soon after you’ve been out driving, you’ll get an inaccurate reading.

Every car has a recommended cold inflation pressure, usually displayed in the owner’s manual, on the sticker inside the driver’s side doorjamb, on the glove box door, or on the fuel filler flap.

Tire pressure typically increases or decreases 1 PSI for every difference of 10 degrees Fahrenheit. The friction between your tires and the road generates heat, so driving raises your tire pressure significantly.

The TIA’s Safety Council recommends that motorists have their own tire pressure gauge in order to easily check cold inflation pressure. Air gauges at service stations, they say, may be inaccurate due to exposure or abuse.

You should make a habit of checking your cold inflation pressure each month, as tires can lose up to 1 PSI every month in addition to pressure losses from weather changes.

How Much Air Do Tires Lose Over Time?

Too often, drivers set their tire pressure and then forget about it. Although tires lose air pressure due to isolated factors like ambient temperature fluctuations and tread punctures, they also simply lose pressure gradually over time.

Most modern cars have tires with recommended pressures between 30 and 35 PSI. On average, these tires lose about 1 PSI per month when they’re left alone. Thus, if you haven’t checked your tire pressure for a few months, you’re probably driving on underinflated tires, and as we’ve mentioned elsewhere, doing so will harm your traction, tire life, steering, and the overall safety of your vehicle. And your tires could be underinflated without triggering your Tire Pressure Monitoring System (TPMS) indicator light, which only illuminates when one or more of your tires falls below 25% of the recommended inflation for your vehicle.

So why do tires lose pressure over time? Rubber is composed of molecular strands that stretch and relax each time the tire rolls, and there is constant force trying to push air through the tire. Some air eventually escapes through microscopic spaces between the rubber molecules.

Because it’s difficult to visually detect low air pressure, it’s important to regularly check your tires. Most experts recommend checking your tire pressure at least once a month and before long trips, and checking it once a week is even better.

How Much Does Tire Pressure Change With Temperature?

Keeping your tire pressure at the proper PSI ensures longer tire life, superior handling, and better traction. Your tires gradually lose air pressure over time, but another factor can affect inflation levels: the weather.

Fluctuations in temperature can have a big impact on the air pressure in your tires. Like other gases, air contracts when it’s cold and expands when it’s hot. By that principle, there’s less air in your tires when it gets cold and more air when it gets hot.

But you might be wondering whether this actually has a measurable, significant effect on your tires. A good metric to keep in mind is that for every difference of 10 degrees Fahrenheit, your tires will lose or gain 1 PSI. If you think about the difference between summer and winter temperatures, that fluctuation is enough to lower your air pressure by 5 PSI when the cold weather sets in. And driving around with your tires at 5 PSI below the recommended pressure will undoubtedly hurt handling and traction; it will also wear out your tires faster.

Another thing to consider: if you’ve parked outside and your tires have been exposed to direct sunlight for a long time, this will also temporarily raise your PSI.

It’s certainly a good idea to keep an eye on your tire pressure as the weather changes. Remember: don’t rely on the warning on your dashboard to tell you when to put air in your tires. Your tires could be getting low enough to negatively affect your gas mileage and steering without triggering the indicator light.

How Do I Inflate My Tires?

Most people refill their tires at gas stations, which usually only costs a few quarters. Alternatively, you can buy a portable air compressor that allows you to refill your tires at home. If your car is due for additional maintenance, such as an oil change or tire rotation, it’s likely that your mechanic will fill up your tires for free.

To determine the correct PSI for your car’s tires:
       - Open the driver’s side door and look at the yellow sticker on the doorjamb
       - Consult your owner’s manual
       - On the glove box
       - Fuel Filler Cap

Do not fill your tires according to the number on the tires themselves. The number on the sidewall of your tire is the maximum PSI, indicating the PSI for which the tire will support the maximum carry load.

At a service station or with your portable air compressor, remove the valve caps from all four tires. Make sure to put the caps in a safe place, like your pocket—they’re easy to lose! Make sure you have your own digital gauge. They typically run about $10, and they’re much more accurate than pencil-style gauges or the ones you’ll find at service stations. Press your tire gauge to the valve stem, letting a little air out to get a reading. To insure an accurate reading, press the tire gauge several times and make note. If the pressure is too low, attach the hose fitting of the air compressor to the valve stem and press down on the lever to allow the flow of air. It is recommended to check your PSI when your tires are cold, before you drive. Make sure it is at a level that is recommended for your car and not what is noted on the tire. Once all four of your tires are inflated to the recommended PSI and your valve caps are replaced, you’ll be good to go!

What is the Correct Tire Pressure?

Every car has a specific tire pressure that will give you optimal handling capabilities and longer tire life. Finding the correct tire pressure for your car is easy.

If you open the driver's side door and look at the doorjamb, there should be a yellow sticker containing a chart. The chart will tell you the correct PSI for your front and rear tires, along with additional information, such as the tire size recommended by the vehicle's manufacturer.

If you can't find the tire pressure placard, you can find the information in your owner's manual. The placard can also sometimes be located on your glove box door or fuel door.

Whatever you do, don't go by the number listed on the tires themselves. The number on the sidewall of your tire is the maximum PSI the tire can hold to carry the maximum load, not the recommended pressure. If you inflate your tires to this pressure, you'll dramatically decrease their lifespan and diminish your car's handling capabilities. The correct tire pressure is probably somewhere between 30 and 35 PSI. Inflating your tires to this pressure will give you a smoother, safer ride while extending the life of your tires.