How to Check Tire Pressure and Tread Depth

Check tire pressure with a gauge when the tires are cold, and fill them to the number on the placard in your driver’s door jamb, not the number on the tire. Check tread with a penny and a quarter: replace a tire by 2/32 inch at the latest, and start shopping around 4/32 inch.

Do both at least once a month, spare included. You can’t tell if a modern radial tire is properly inflated just by looking at it, so a gauge isn’t optional.

Time: A few minutes per tire.

Difficulty: Easy.

What you need

A tire pressure gauge. The U.S. Tire Manufacturers Association (USTMA) says one marked in 1 PSI steps up to 60 PSI is enough for most passenger tires. Keep it in the car.
A penny and a quarter, or a tread depth gauge
An air source, such as a home compressor or a gas station air pump
A flashlight, if you’re checking in poor light

Part 1: Tire pressure

Find your number

The recommended pressure is on the tire placard or certification label, usually on the driver’s door jamb, and in your owner’s manual. Front and rear can be different, so read the whole label.

The number molded on the tire sidewall is something else. That’s the maximum the tire can hold, not the pressure your car needs.

Check it, step by step

Start with cold tires. Cold means the car has been parked for at least 3 hours, or driven less than a mile at moderate speed. Driving warms the air inside and raises the reading.
Take off the valve cap. Put it somewhere you won’t lose it.
Press the gauge onto the valve stem. Push it on straight and firmly until the hiss stops, then read the number.
Compare it with the placard. Write down all four readings if that’s easier.
Add air if it’s low. Use short bursts and recheck as you go. Never fill past the maximum on the sidewall.
Let some out if it’s high. Press the small pin in the center of the valve briefly, then check again.
Refit the cap. Valve caps keep out moisture and dirt, and they add a second seal.
Repeat on every tire, then do the spare. A flat spare is no use on the side of the road.

The spare

Check full-size and temporary spares monthly and before long trips. USTMA says T-type temporary spares need 60 PSI, but check your tire and manual to confirm what yours needs. Add air in small amounts, since small spares change pressure quickly.

Why the warning light isn’t enough

Your tire pressure monitoring system is a backup, not a replacement for a gauge. Federal rules require a warning when a tire is 25 percent or more below the recommended pressure, and a tire that low is already well under where it should be. USTMA also warns that some systems may only detect differences between tires, so all four losing air together may not trigger the light.

Heat and cold

Tires can lose 1 to 2 PSI a month under normal conditions, plus 1 to 2 PSI for every 10 degree Fahrenheit drop in temperature. That’s why a warning light can come on during a cold snap.

Never let air out of hot tires. Pressure normally climbs above the cold figure while you drive. If a hot tire reads at or below the recommended cold pressure, it may be dangerously low, so get it checked right away.

Part 2: Tread depth

New tires usually start at about 10/32 to 11/32 inch. There are four easy ways to see how much is left.

Check	How to do it	What it means
Wear bars	Look for narrow strips of smooth rubber across the tread grooves	If a bar is flush with the tread, the tire is worn to 2/32 inch and should be replaced
Penny test	Put a penny in the groove with Lincoln’s head upside down, facing you	If you can see all of his head, you’re at or below 2/32 inch. Replace the tire.
Quarter test	Put a quarter in the groove with Washington’s head upside down	If you can see the top of his head, you’re near 4/32 inch. Start shopping.
Tread depth gauge	Press it into the groove and read the scale	The most precise check

Where to check

Test several grooves on each tire: the inside, the center, and the outside. Check a few spots around the circumference as well. Tires don’t always wear evenly, and the lowest reading is the one that counts. If any area fails, the tire fails.

Run your eyes across the tire while you’re down there. Uneven wear can point to an alignment, inflation, or suspension problem. Rotation helps tires wear evenly. Follow your owner’s manual for the interval. If it doesn’t give one, USTMA suggests every 5,000 to 8,000 miles.

Why 4/32 inch?

The 2/32 inch mark is the point where a tire is worn out, not the point where it stops getting worse. Consumer Reports says wet braking, hydroplaning resistance, and snow traction all decline as tires wear. At 4/32 inch, you still have some all-weather grip left and time to shop. Ford also suggests replacing tires around 4/32 inch for better traction in rain or snow.

What the law says

Legal limits vary by state. Most states use 2/32 inch for passenger cars. Some are different: California’s statute, for example, sets 1/32 inch in any two adjacent grooves as its general minimum, and a few states have no numeric limit and rely on general unsafe-vehicle rules. Check your state’s DMV or vehicle code for your local rule, and treat it as the bare minimum, not a safety target.

Common mistakes

Using the sidewall number. It’s a maximum for the tire, not a target for your car. Go by the placard.

Checking after a drive. A warm tire reads high, so you might think it’s fine when it’s actually low. Check first thing in the morning if you can.

Waiting for the dash light. By the time it comes on, the tire may be 25 percent low. Use your gauge monthly.

Forgetting the spare. You only find out it’s flat when you need it most.

Testing one groove. Inner edges can wear out while the center looks fine. Check across the whole tire.

Ignoring a slow leak. Topping up the same tire over and over is a warning sign, not a routine.

Add these checks to your car care checklist so they become a habit. They pair well with cleaning: you’ll be right next to the tires during a wheel and tire clean, and a monthly walkaround is a good time to check your fluids and your wiper blades too.

When to hire a pro

For this job, your pro is a tire shop, not a detailer. Go to one if:

A tire keeps losing more than 2 PSI a month
You find a cut, bulge, puncture, or exposed cords
You see uneven wear on one edge or in patches
The warning light stays on after you’ve set the correct pressure
Your tread is at or near the limit and you need new tires

Any tire that keeps needing air is a serious safety risk, so have it inspected right away and don’t just keep topping it up.