How to Check and Add Air to Car Tires

Keeping the appropriate air pressure in your tires is one way to help maintain the safety of your vehicle. Low air pressure can lead to accidents, extra wear on your tires and overuse of gasoline. Learning how to check and add air to car tires is an essential skill that every driver should master.

1) Purchase tire gauge from an auto store or auto department of a hardware store. Tire gauges measure pounds per square inch (standard) or kilo Pascal's (metric).

2) Determine how much air should be in your tires. 

Look at the writing on the side of your tires or on a sticker on the inner panel of the door. The tire will have a recommended PSI or KPA number. This is the pounds per square inch or kilo Pascal's that your tires need. You can also check your owners manual for this information

3) 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

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

 5) Place the tire gauge onto the tire valve stem

6) Press the tire gauge firmly down on top of the valve stem, and Read the gauge to gain information about the PSI or KPA in your 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

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 over inflate 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.

Source: WikiHow