Tire pressure and when to replace tires

Why tires matter so much

No matter how good the brakes or safety systems are, every bit of stopping and steering force passes through four contact patches roughly the size of your palm. Tires with the wrong pressure or worn tread stop in a longer distance and cannot clear water on wet roads, so the car slides. Because tires change gradually, people who drive every day are often the last to notice. That is why a fixed routine, such as checking by eye and with a gauge once a month, is so valuable. It takes a few minutes, and missing a problem can cost far more.

Where to find the recommended pressure

The most common mistake is inflating to the number on the tire's sidewall. That figure is the maximum the tire can hold, not the recommended pressure. Your car's recommended pressure is usually on a placard on the door frame or door edge when you open the driver's door, inside the fuel filler flap, or in the owner's manual. Front and rear values may differ, and there may be a separate figure for a fully loaded car. If you fitted tires in a size different from the original, ask the seller or a shop for the correct value.

• Placard on the driver's door frame or door edge
• Inside the fuel filler flap
• Tire section of the owner's manual
• Check for different front, rear, and loaded values

How to measure

Measure pressure when the tires are cold, meaning before driving or after the car has sat for a few hours. Driving warms the air inside and raises the reading, so if you let air out to match the recommended value while the tires are hot, they will be underinflated once they cool. A pump at a gas station or shop, or your own gauge, will do. Pressure drops as the air temperature falls, so check more often in late autumn and early winter. Even if your car has a pressure warning light, it often comes on only after pressure is already well down, so it does not replace checking yourself. If you carry a spare, check it now and then too.

What wrong pressure does

An underinflated tire squashes more, flexes its sidewalls too much, and builds up heat. Fuel economy suffers, both shoulders wear faster, and in severe cases the tire can fail at speed. An overinflated tire has a smaller contact patch, so grip drops, the center wears faster, and the ride gets harsh. More is not better, and less is not gentler. The recommended value is the balance point for mileage, braking, and tire life. If one tire keeps losing air faster than the others, it may have a nail in it or a wheel problem, so have it checked.

Reading the wear limit

At the bottom of the grooves are raised wear bars set at a fixed depth. Look for a small triangle or similar mark on the sidewall and follow that line into the tread to find them. When the tread wears down level with these bars, the tire must be replaced. Under Korean rules that limit is a groove depth of 1.6 millimeters, and many other countries use a similar figure. It is only a legal minimum, though. Wet and snowy performance drops as grooves get shallower, so replacing tires before they reach the limit is the safer choice. Uneven wear on one side may point to pressure or alignment problems, so have those checked as well.

• The wear bars are level with the tread
• Only one shoulder or the center is worn
• The car feels like it slides on wet roads

Date codes and aging

Tires are rubber, so they harden and crack with age even if they are not driven much. The sidewall carries a four-digit date code: the first two digits are the week of the year and the last two are the year. A code of 2523, for example, means the tire was made in the 25th week of 2023. Even with plenty of tread left, many fine cracks in the sidewall or rubber that has gone hard are reasons to talk to a tire professional. Guidance on how many years a tire can stay in service varies by manufacturer, so check the tire maker's official advice. It is worth checking the date code when you buy new tires, too.

Signs that need immediate attention

If a sidewall has a bulge, a deep cut, or exposed cords, do not keep driving on that tire. Sidewall damage is often not repairable and can cause a sudden blowout at speed. A shaking steering wheel, a pull to one side, or new vibration or noise can also signal a tire or wheel problem. If a tire bursts while you are driving, do not brake hard or jerk the wheel. Hold the steering firmly, let the car slow down gradually, and pull over somewhere safe. On a highway, stop on the shoulder, turn on the hazard lights, move to a safe spot away from traffic, and then call for help.

Rotation and replacement tips

Front and rear tires do different jobs and wear at different rates. Rotating them according to the interval and pattern in your manual helps all four wear evenly and last longer. When replacing, try to change both tires on the same axle together, and make sure the size and load and speed ratings suit your car. Replacing just one can leave left and right with different grip. Many manuals also recommend rechecking wheel nut tightness after a tire change or repair, so follow that advice. This guide explains general principles only. Base actual pressure and replacement decisions on your car's manual and an inspection by a tire professional.