The right tire pressure is the one printed on your vehicle's placard, not the number moulded into the tire's sidewall. Tires are worn out when the tread reaches the wear bars, or when they are simply too old, whichever comes first.
Why the placard and not the tire? The sidewall number is the maximum the tire can safely hold. The placard is what the vehicle's engineers chose for that weight, that suspension and that handling. On cars, SUVs, vans and pickups it is a sticker on the driver's door frame or inside the fuel flap. On motorcycles it is usually on the swingarm or chain guard, and always in the manual. Trailers and many RVs are the exception: they run close to the tire's rated load, so the placard often matches the sidewall maximum. Bicycles print a range on the tire, and the lower end is for comfort and grip.
Under-inflation is the expensive mistake. A tire running below its placard pressure flexes more, runs hotter, wears its shoulders and burns extra fuel on every trip. Over-inflation wears the centre of the tread and reduces grip in the wet. Both shorten the tire's life.
Check it yourself:
- Check cold: before the first drive of the day, or after at least three hours parked. Driving warms the air inside and adds pressure, so a warm reading always looks better than it is.
- Check monthly, and before any long or heavily loaded trip. Pressure falls with the weather too: about 1 PSI for every 10 °C (0.07 bar per 10 °C, or 1 PSI per 18 °F) the temperature drops.
- Use your own gauge. The gauges on station air hoses are often inaccurate. Do not forget the spare, and on a trailer or RV, every tire on every axle.
- Find the wear bars: small raised strips running across the bottom of the main grooves. When the tread surface is level with them, the tire is at the legal minimum in most countries (about 1.6 mm, or 2/32 of an inch) and should have been replaced already. Winter tires need roughly double that to work in snow.
- Track the depth: a tread depth gauge costs very little. Without one, stand a coin in the main groove, note how much of it disappears, and compare the same spot next month. The change is what you are watching, along with any difference between the inner and outer edges, which points to alignment or pressure.
- Read the age: the last four digits of the code on the sidewall are the week and year the tire was made (for example 2322 is the 23rd week of 2022). Rubber hardens with age, so many manufacturers advise replacing tires around six years old even with tread left, and ten years is a common hard limit. Trailer, RV, boat-trailer and classic-car tires usually age out long before they wear out.
Rotation and alignment: on cars, SUVs, vans and trucks, rotating the tires at every oil change or roughly every 10,000 km (6,000 miles) spreads the wear evenly and is the cheapest way to make a set last. Motorcycles and single-axle trailers have no rotation pattern. Get an alignment checked when the vehicle pulls to one side, the steering wheel sits off-centre, the edges wear faster than the middle, or after a hard pothole or curb strike.
Whatever you find, log it: the pressures you set, the tread depth at each corner, and the odometer at every rotation. Next month you will be comparing against a real baseline instead of a memory, and a slow leak or a fast-wearing corner shows up long before it becomes a roadside problem.
Sep 8, 2026