Tire Pressure Check: How Often, When and What Number

The correct pressure is set by the vehicle manufacturer for that vehicle, its load and its tire size. It is printed in two places:

• The placard, usually a label on the driver's door jamb. Some vehicles put it inside the fuel door or the glove box.
• The owner's manual, which often also gives a figure for carrying a full load or towing.

Front and rear pressures can differ, and many pickups list a higher rear pressure for loaded use. Read the whole label, not just the first number.

The sidewall number is not the target

Every tire carries a pressure molded into its sidewall. That is the maximum the tire is built to hold, not the pressure your vehicle should run. Inflating to the sidewall figure usually overinflates the tire for everyday driving, which reduces grip and wears the center of the tread.

Driving warms a tire, and warm air in a tire reads higher on a gauge. A reading taken after a drive across town can look correct while the tire is actually low.

"Cold" means the vehicle has been parked for a few hours, or driven only a short distance. First thing in the morning is the simplest time. If you have to check warm, do not let air out to reach the placard figure; check again once the tires have cooled.

Outside temperature matters too. Pressure falls as the weather cools, so the first cold mornings of fall are a common time for warning lights to come on. A tire that was correct in summer can be low in winter without any leak.

Once a month as a habit, plus:

• Before a long trip
• Before towing or carrying a heavy load
• After a large drop in outside temperature
• Whenever a tire looks low, or the pressure warning light comes on

The warning light is a backstop, not a schedule. On many vehicles it only comes on once a tire is well below the right pressure, by which point it has already been running low.

1. Use a reliable gauge. A simple handheld gauge works if it is kept in good condition; a dropped or damaged one can read wrong.
2. Remove the valve cap and press the gauge firmly onto the valve.
3. Compare the reading with the placard figure.
4. Add air in short bursts and recheck until it matches.
5. Replace the valve cap, which keeps dirt and moisture out of the valve.

Do not forget the spare if the vehicle has one. It is the tire most often found flat on the day it is needed.

Too low. The tire flexes more, builds heat, wears both shoulders, and handles less precisely. Serious underinflation can lead to failure. It also costs fuel.

Too high. The tire has a smaller contact patch, less grip, a harsher ride, and wears the center of the tread.

Uneven between tires. The vehicle may pull or feel unsettled. A tire that needs air every week or two has a slow leak and should be looked at. The article on flat tire repair covers what happens next.

A vibration at speed is usually not pressure. It is more often balance, covered by tire and wheel balancing.

The everyday placard figure assumes an ordinary load. When that changes, the right pressure can change too.

Carrying weight. Many pickups and SUVs list a separate, higher figure for a full load. A truck bed full of materials or a cargo area packed for a trip is the case it is written for. Check the manual and set pressures before you load up, while the tires are cold.

Towing. The tow vehicle's rear tires carry part of the trailer's weight through the hitch. The owner's manual often gives a towing figure, and following it helps the vehicle stay stable.

The trailer itself. Trailer tires have their own pressure, usually on a placard on the trailer or in its documentation. They are frequently forgotten because they sit unused for long periods and lose air slowly while parked. A trailer that has been parked for a season should have its pressures checked before it moves.

Back to normal afterwards. Once the load is off, return to the everyday figure. Running loaded pressure on an empty vehicle makes the ride harsher and wears the center of the tread.

On trucks and trailers the same rules apply with more at stake. Duals on the same axle end should be at matching pressure; a low inner dual pushes load onto its partner and can ruin both. Fleets usually make pressure checks part of a regular inspection routine. The fleet tire program article covers building that routine.

Most Purcell locations that fit passenger tires can check and set pressures while the vehicle is in. Ask the store when you visit. Current service offers vary by location and are listed on the service offers page.