Correct tire pressure is free, takes five minutes, and does more for how a car drives and what it costs to run than almost anything else you can do to it.
- Time: 5 minutes to check, 20 to plug a nail hole
- Difficulty: beginner
- You need: a $10 gauge, and a $15 plug kit if you want to fix punctures
Checking the pressure
The number you want is on the driver’s door jamb, not on the tire.
Open the driver’s door and look at the sticker on the frame. That is the pressure the manufacturer specifies for your car, usually 32 to 35 psi. The big number moulded into the tire sidewall is the tire’s maximum, not the recommended figure — inflating to that is a common and uncomfortable mistake.
- Check them cold — first thing in the morning, or at least three hours after driving. Driving heats the air and adds several psi, which makes a low tire read normal.
- Unscrew the valve cap and put it in your pocket, not on the ground.
- Press the gauge straight onto the valve firmly. A brief hiss is normal; a continuous hiss means it is not square on.
- Read it, and do all four. Front and rear are sometimes different — the door sticker says.
- Check the spare a couple of times a year. A flat spare is a bad surprise at the worst moment.
Adding air: most gas stations have a pump, often free or a dollar. Add in short bursts and re-check — it goes in faster than you expect. If you overshoot, press the small pin in the centre of the valve to let some out.
Why it matters: under-inflated tires wear out at the edges, use more fuel, handle worse, and run hot — and heat is what causes blowouts. Tires lose about a pound a month on their own, plus a pound for every 10°F the temperature drops. That is why the warning light appears on the first cold morning of autumn.
The tire pressure light
Steady light: at least one tire is low. Check all four and inflate to the door sticker. On most cars the light goes out by itself after driving a few miles. Some cars have a reset button under the dash or a menu item in the instrument cluster — the manual says which.
Flashing light, then staying on: that is different. It means the monitoring system itself has a fault — usually a dead sensor battery in one wheel, which is a shop job and typically $50 to $100 per sensor. The tires may be perfectly fine.
If the light comes back within a day or two of inflating, you have a slow leak. Which brings us to the next part.
Plugging a nail hole
Only plug the tread — the flat part that touches the road.
Never plug a sidewall or the shoulder where the tread curves. Those flex constantly, a plug there will not hold, and it can fail at speed. Never plug a hole bigger than about a quarter inch. And a tire that has been driven on while flat may have internal damage you cannot see — that one goes to a tire shop.
A plug is widely treated as a temporary repair. The permanent version is a patch fitted from the inside, which means dismounting the tire. Most tire shops will do a proper patch for $25 to $45, and many will do it free if you bought the tires there.
- Find the hole. Spray soapy water over the tread and look for bubbles, or listen. Often the nail is still in there.
- Leave the wheel on the car if you can reach the hole by rolling the car forward a little. No jacking needed.
- Pull the nail with pliers. Air will start escaping. That is expected.
- Ream the hole with the rasp tool from the kit — push it in and out several times. It feels aggressive and it is meant to; it roughens the hole so the plug grips.
- Thread a plug into the insertion tool so equal lengths hang out each side, and coat it with the cement from the kit.
- Push it in hard until about a half inch is left showing, then pull the tool straight out. The plug stays behind.
- Trim the plug flush with a blade and inflate to the door-sticker pressure.
- Check it with soapy water and check the pressure again the next morning.
While you are down there
The penny test for tread depth. Put a penny into a tread groove with Lincoln’s head upside down and facing you. If you can see the top of his head, the tread is at or below 2/32 of an inch and the tire is legally worn out. Do that at several points around each tire.
Also glance at how the tread is wearing. Both edges worn and the middle fine means chronic under-inflation. The middle worn and the edges fine means over-inflation. One edge only means an alignment problem, which no amount of air will fix.
Information only, not professional advice. Work on your own vehicle is at your own risk. See the disclaimer.