Why a monthly check is worth the minute
Tires lose a little air all the time, even when nothing is wrong, and air pressure also changes with the weather. A tire can be noticeably low without looking flat, especially on modern low-profile designs. Running under-inflated causes extra wear, can hurt handling and braking, and slightly raises fuel use. Checking takes only a few minutes with a cheap gauge.
What you need
- A tire pressure gauge: a simple stick type, a dial gauge or a digital one. Any of them works if it is accurate and readable.
- An air source: a home or portable compressor, a hand or foot pump, or a pump at a service station.
- The valve caps, which should go back on afterward to keep dirt out of the valve.
A gauge built into a station pump can be inaccurate, so many people keep their own gauge for the actual reading.
Find the right pressure for your car
The correct pressure is set by the vehicle maker for your particular car, not printed as a target on the tire. Look in these places:
- A label on the driver’s door jamb, door edge or pillar
- The fuel filler flap on some cars
- The owner’s manual
The label may list different figures for the front and rear, or for normal and heavily loaded use. It is normally given in psi, kPa or bar. As a rough conversion, one bar is about 14.5 psi. Do not use the maximum pressure printed on the tire sidewall; that is the tire’s limit, not the recommended pressure for your car. The sidewall details are explained in the guide to sidewall markings.
Check when the tires are cold
Driving heats the air inside a tire and raises the reading. The figure on the label assumes a cold tire, which usually means the car has been parked for a few hours or driven only a short distance, often under a mile or two. If you must drive some distance to a pump, check the pressure at home first, or note how much the reading changes and adjust carefully. Avoid letting air out of a warm tire to hit the cold figure, since it will end up too low once the tire cools.
Temperature also matters. Air pressure tends to drop in cold weather and rise in hot weather, so a check at the start of winter or after a big temperature change is a good habit. This is one reason a dashboard pressure monitoring light often comes on during the first cold snap.
Step by step
- Park on level ground and let the tires cool, ideally overnight or for at least a few hours.
- Remove the valve cap from the first tire and keep it somewhere safe.
- Press the gauge firmly onto the valve stem in a straight line. You should hear a brief hiss, then it stops. A hiss that continues means the seal is poor, so reposition and try again.
- Read the number and write it down.
- Compare it with the figure on the label. Hypothetically, if the label says 35 psi and your gauge reads 30 psi, the tire is 5 psi low.
- Add air in short bursts, rechecking between bursts, until the reading matches. If you overshoot, press the small pin in the center of the valve briefly to release air, then check again.
- Refit the valve cap and repeat for every tire, including the spare if the car has a full-size or space-saver one. Spares often need a different, higher figure, which is usually printed on the spare itself or in the manual.
Things that are easy to get wrong
- Using the sidewall number instead of the vehicle’s figure.
- Checking warm tires and then adding air to a reading that is falsely high or low.
- Trusting your eyes. A tire can lose a significant share of its pressure and still look fine.
- Ignoring one tire that keeps dropping. If one tire needs air much more often than the others, there may be a slow leak, as covered in the article on what to do about a slow puncture.
- Forgetting the load. Some cars list a higher figure for carrying a full load or towing.
If the warning light is on
A dashboard light for low tire pressure means one or more tires have dropped significantly below the set level. Do not just reset it. Check all tires with a gauge, fill to the correct figure and see whether the light goes out, possibly after a short drive. If it stays on or returns, a tire may be leaking or a sensor may be at fault, and a shop can check. The full explanation is in the article on the tire pressure monitoring light.
How often to check
A common recommendation is about once a month and before long trips or when the load changes, such as when you carry passengers and luggage on a road trip. Also check after a big change in temperature. When you are in the habit, it takes less time than filling a drink bottle.
If you are ever unsure about the figure for your car or about a tire that seems damaged, ask a tire technician. Recommendations vary between vehicles, so your manual is the final word.