How to Check Air Pressure in Tires

Inaccurate pressure can cause poor mileage, uneven tire wear, or a tire blow-out. To prevent these events from happening it is important to maintain proper tire pressure.

Steps

1. 1
   Make sure the tires are "cold" (vehicle hasn't been driven for more than 2km) so the air in the tires isn't expanded from heat.

   
   
2. 2
   Look in the owners' manual or (on most vehicles) on the inside of the driver's side door for the standard cold tire inflation pressure. This number is the lowest PSI one would inflate the tires to and is suggested by the car's manufacturer. Read below for reasons inflation may be placed higher.
3. 3
   Unscrew the valve stem cap from the valve stem on the tire. The valve stem is a black pencil-sized extension near the hubcap, about 1" (2-3 cm) long.
4. 4
   Press the air pressure gauge onto the valve stem and record the reading given. If there is a hissing sound, the gauge is not tight enough for an accurate reading. The angle of the gauge may need to be adjusted.
5. 5
   Note that if the reading is the same as the manual's specifications, you are done after checking all other tires for the same pressure. If inadequate pressure is in the tires then fill air in the tires. Make sure you put in the correct amount.
6. 6
   Replace valve stem cap. The cap does not hold air in, but it keeps dirt and moisture away from the valve mechanism in the valve stem, which does hold air in.

   
   

Video

Tips

• The PSI listed on the sidewall of the tire is the max cold pressure for the tire carrying the highest (weight) load the tire supports.
• Increase the cold tire pressure if the car will be carrying a heavy load or driven at high speeds for long times.
• Cold weather will reduce the air pressure, warm weather will increase the air pressure - it is important to recheck tire pressure when the seasons change.
• Additional fuel economy and improved steering response can be obtained at the price of a firmer ride if the tire's inflation is increased above what is recommended by the car's manufacturer. This shouldn't exceed the max pressure listed on the tire's sidewall. Test the car to see if its driving feel is improved.
• If the car has to be driven to add air note the pressure before driving away. Then add the difference above when the reading is now. For instance if you wish to inflate your tires to 35psi and they're reading 30psi cold. The tires are 5psi underinflated so when you add air after driving and they now read 33psi adjust them to be 38psi. They should then read 35psi when cold.
• Sunlight heats up tires even if they're not driven. For more even readings take note that not one side of the car has sun shining on it.
• Tires cannot be "eye-balled" for pressure, particularly modern radials. Always use an accurate gauge.

Warnings

• An underinflated tire causes more sidewall flexing that increases stopping distance, lowers fuel economy and shortens the life of a tire. In rare cases the tire can blowout because of excessive heat from too much sidewall flexing and can even roll off the wheel in emergency maneuvers.
• An overinflated tire (filled above the max cold pressure on the sidewall) makes for a harsher ride and makes it more prone to damage if you hit pot-holes or other objects in the road.
• Do not rely solely on the air pump gauge at the gas station. These pumps take a lot of abuse (slammed against concrete, ran over, etc.) and may not be calibrated properly...it is best to fill your tire "above" the recommended PSI, using the gauge on their pump, but then once done, check the tires using "your" gauge. Always base your final readings using "your gauge" for best accuracy.

Things You'll Need

• Tire pressure gauge of good quality. Do not rely on 'pencil' type tire gauges. Professional quality tools always pay for themselves over time; buy a professional quality tire gauge.
• Air compressor or pump with correct fitting (bicycles can have one of two types: Presta or Schrader - Schrader is the type used by cars and assumed in the description above)...