Get better gas mileage - How to check your tire pressure

Inflating and maintaining proper tire pressure ensures safer, more comfortable driving and better fuel efficiency. Particularly in times of high gas prices; in inclement driving conditions such as heavy rain, snow, or ice; and in vehicles of all sizes, tire pressure can make a major difference in driving, wherever you are.

Given the importance of the task, you might think it is complicated, but checking and maintaining your tire pressure is simple, provided you have a good tire air pressure gauge and source of air, both of which are available at many gas stations.

Get a Gauge

A simple tire air pressure gauge, available at most auto parts stores, for a few dollars, is adequate for the job. You do not necessarily need a digital air pressure gauge. If it is worth the $14 to $15 to you, a digital pressure gauge is easy to read and accurate. However, you should consider whether it will require batteries, and whether this would prevent you from using it.

Again, a standard pressure gauge that measures pounds per square inch (PSI) and fits easily in the glove box of your vehicle, is sufficient. Do avoid ultra-cheap models that may not give a proper reading.
As for a source of air, many gas and service stations have air available for 50 cents or so. Some of these air machines have gauges on them, and if you have no other means of measuring the pressure of your tires, these will work. However, they are typically beat and inaccurate, so have your own gauge to ensure the proper PSI for your tires and vehicle.

Checking Pressure

PSI is measured by the notches on a tire air pressure gauge or with a number reading on digital gauges. To find out what PSI is right for your tires, consult your owner's manual or the sticker on the driver's side door. When buying new tires, or getting a rotation, it's a good idea to ask what the ideal pressure is.

Recommendations may vary, but you should never inflate the tires five PSI more or less than what is recommended. Under-inflating wears out the sides of the tire, and is actually a driving hazard. Over-inflated tires will wear more quickly, and are also dangerous because of the increased possibility of a blowout. If you are unsure about the PSI for your tires, or it is unclear or worn away on the side of your tires, ask your mechanic or someone who knows about vehicles what PSI you should have for your tires.

Smaller compact and mid-size sedans typically have PSI levels between 30 and 40 PSI. Larger vehicles with larger tires, including bigger sedans, usually have higher pressure, around 45 PSI. These are general PSI figures, and the most accurate PSI for your tires is the number listed on the side. Tires should all be inflated to the same PSI for safety, proper vehicle function, comfort, and fuel efficiency.

Also, check your vehicle's tire pressure when the tires are cold. This means the tires should not have been driven on for at least three hours. If you need to drive to get air, try to drive less than a mile.
To get a PSI reading on your tire, place the air pressure gauge onto the tire's valve stem, the pencil-width air nozzle on the side of the tire. Try to place the gauge evenly onto the valve stem. This will allow air to escape, but once you firmly press the gauge down on the valve stem, it will stop the flow of air and give your gauge a reading, either by blowing out the metered stick with a traditional gauge, or a reading with a digital model gauge.

Adjusting Tire PSI

So you have a tire pressure gauge, and a source of air. It is best if you can park your car centered on the source of the air, which usually has a hose to reach the vehicle's tires. You may need to move the car to reach all of the tires, depending on the situation. Before you pay any money for air or start pumping up your tires, remove the caps on all the tire valve stems.

Next, you should check the pressure of all four tires, noting which ones need the most air. This will help you maintain uniform pressure in the tires, some of which may need less air. Hot weather, extreme temperatures and other conditions can cause the air in your tires to expand, and PSI can subsequently increase.

Once you know which tires need more air, you can deposit coins into the air machine, or get your air hose ready. Choose the first tire to fill, and fit the air hose nozzle onto the tire stem. When you start to place the air hose onto the tire stem, it will hit a pin inside the stem and start leaking air. You know when you have the air hose nozzle properly applied when the leaking air stops. It takes some force to get the hose pressed firmly on, but once it is in place, you will be ready to increase the tire pressure.
Some air hoses are automatic, and will release air in your tire once you have it on the tire's valve stem. Other air hoses have handles and require you to squeeze them to activate the air.

It is important to have your gauge as you fill the tire, taking the hose off somewhat frequently to check the pressure. It is extremely important not to over-inflate your tires. You can avoid this by using small bursts of air between your checks. As you increase the PSI and keep checking it, you will get a feel for how much air you are putting into the tire, and how much more you need. Once you get close to your recommended PSI, use less air, and keep going until you are at the right level.

Once you have the tires properly inflated, replace the stem caps by screwing them back on. Do not over-screw them, as they will break on the top. Tire stem caps are important to keep your tire valve stems clean and undamaged.

Tire pressure should be checked weekly, or every other week at least. Particularly with severe weather and temperature swings, tire pressure on the nicest tires with the nicest cars can still fluctuate, and must be monitored and maintained regularly for safe and fuel-efficient driving.