How to Check Tire Pressure and Tread Depth
How to check tire pressure correctly and measure tread depth with a gauge, penny or quarter, plus when to replace tires and how to read the sidewall date code.
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Tires are the only part of your car that touches the road, and two simple checks tell you most of what you need to know about them: pressure and tread depth. Both take about five minutes with tools that cost a few dollars. Do the pressure check monthly and before long trips, and the tread check every few months or at each oil change.
What you need
- A tire pressure gauge. Digital or dial gauges are generally easier to read than pencil gauges. The gauge on a gas station air hose is often inaccurate.
- A tread depth gauge (inexpensive at any parts store), or a penny and a quarter.
- An air source: a portable 12-volt inflator or a gas station air pump.
- A flashlight for inspecting sidewalls.
How to check tire pressure
Find the right pressure
Look for the Tire and Loading Information placard on the driver's door jamb. It lists the recommended cold pressure for the front, rear and spare. It may also be in the owner's manual or on the fuel door.
Check when the tires are cold
"Cold" means the car has been parked for at least three hours, or driven less than a mile. Driving warms tires and raises pressure by several psi, so a hot reading will look higher than it really is. Never let air out of hot tires to match the placard.
Step by step
- Remove the valve cap and put it somewhere you will not lose it.
- Press the gauge firmly and squarely onto the valve stem until the hissing stops.
- Read the pressure. Repeat for a second reading if it seems off.
- If low, add air in short bursts and recheck. If high, press the small pin in the center of the valve briefly to release air.
- Replace the valve cap; it keeps dirt and moisture out of the valve.
- Do all four tires, and the spare if you have one. Compact spares often need around 60 psi; check the placard or the spare itself.
How often
At least once a month, before long trips, and after big temperature swings. Pressure typically drops about 1 psi for every 10°F drop in air temperature, which is why a TPMS warning often appears on the first cold morning of fall.
What TPMS does and does not do
Cars sold in the US since the 2008 model year have a tire pressure monitoring system. Under the federal standard, it warns when a tire is significantly underinflated, at 25% or more below the recommended pressure. That is a safety net, not a substitute for a gauge: a tire can be noticeably low before the light comes on. See why the TPMS light stays on.
How to check tread depth
Tread depth is measured in 32nds of an inch. Most new passenger car tires start at around 10/32 to 11/32 inch; truck and winter tires often more.
With a tread depth gauge (most accurate)
- Push the gauge's probe into a main groove (the deep channels running around the tire).
- Press the gauge flat against the tread blocks on either side.
- Read the depth.
- Measure the inner, center and outer grooves on each tire, and at a couple of points around the circumference. Record the lowest number.
The penny test
Insert a penny into a 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 inch, and the tire should be replaced.
The quarter test
Insert a quarter with Washington's head upside down. If you can see the top of his head, tread is about 4/32 inch or less, and it is time to start shopping for tires.
Tread wear indicator bars
Tires have small raised bars across the bottom of the main grooves, set at 2/32 inch. When the tread is flush with these bars, the tire is worn out.
When to replace your tires
| Tread depth | What it means |
|---|---|
| 10/32 to 11/32 in | Typical new passenger tire |
| 6/32 in | Snow traction declining; consider replacing before winter if you drive in snow |
| 4/32 in | Wet-road braking noticeably reduced; plan replacement soon |
| 2/32 in | Legal minimum in most states; replace now |
- 10/32 to 11/32 in
- What it means
- Typical new passenger tire
- 6/32 in
- What it means
- Snow traction declining; consider replacing before winter if you drive in snow
- 4/32 in
- What it means
- Wet-road braking noticeably reduced; plan replacement soon
- 2/32 in
- What it means
- Legal minimum in most states; replace now
Grip in rain falls off well before the legal limit, because shallow grooves cannot clear water fast enough, increasing the risk of hydroplaning. Many safety experts recommend replacing tires at about 4/32 inch. Check your state's specific legal limit.
Age matters too
Rubber ages even when a tire has lots of tread. The DOT code on the sidewall ends in a four-digit date: the first two digits are the week, the last two the year. "2421" means the 24th week of 2021. Many vehicle and tire makers recommend having tires inspected annually after about 5 or 6 years and replacing them by about 6 to 10 years old regardless of tread; check your owner's manual and the tire maker's guidance. NHTSA's tire safety page (opens in a new tab) explains how to read the full sidewall code.
Read the wear pattern
Uneven wear tells you something is wrong.
| Wear pattern | Likely cause |
|---|---|
| Both outer edges worn | Underinflation |
| Center worn | Overinflation |
| One edge worn | Wheel alignment (camber or toe) |
| Cupping or scalloped patches | Worn shocks or struts, or imbalance |
| Feathered tread blocks | Toe alignment |
| One tire much more worn | Missed rotations, a dragging brake, or alignment |
- Both outer edges worn
- Likely cause
- Underinflation
- Center worn
- Likely cause
- Overinflation
- One edge worn
- Likely cause
- Wheel alignment (camber or toe)
- Cupping or scalloped patches
- Likely cause
- Worn shocks or struts, or imbalance
- Feathered tread blocks
- Likely cause
- Toe alignment
- One tire much more worn
- Likely cause
- Missed rotations, a dragging brake, or alignment
Regular rotation evens out normal front-to-rear wear; see how often to rotate tires. Persistent uneven wear needs an alignment check.
Inspect the sidewalls and tread surface
While you are down there, look for:
- Bulges or bubbles in the sidewall, which mean internal damage. Replace the tire; it can fail suddenly.
- Cuts, cracks or exposed cords.
- Nails or screws in the tread. Many punctures in the central tread area can be properly repaired with a plug-patch from the inside; punctures in or near the sidewall generally cannot.
- Fine cracking (weather checking) between tread blocks or on the sidewall, a sign of age.
Buying replacement tires
- Match the size, load index and speed rating on your door placard. Decode a tire size like 225/45R17 91V with our tire size calculator.
- Replace tires at least in pairs on the same axle. Many AWD vehicles need all four replaced together, or closely matched tread depths; check your owner's manual.
- New tires generally go on the rear axle when replacing only two, for stability.
- Register new tires with the manufacturer so you are notified of recalls, and check tire recalls on our recalls pages.
- Note the date, mileage and tread depth in a free CarManager garage to track how fast your tires wear.
Compare two sizes and decode load index and speed rating.
Frequently asked questions
How often should I check my tire pressure?
At least once a month and before long trips, with the tires cold. Also check after a big temperature drop, since pressure falls about 1 psi for every 10°F.
Is the penny test accurate?
It is a reliable way to spot tires at the 2/32 inch legal limit, but by then wet grip is already reduced. The quarter test (about 4/32 inch) or a tread depth gauge gives you earlier warning.
What tire pressure should I use?
Use the cold pressure on the placard on your driver's door jamb or in the owner's manual. The number on the tire sidewall is the maximum pressure, not the recommended one.
Should I check pressure when tires are hot?
No. Hot tires read several psi higher than cold ones. If you must add air on the road, fill to about 3 to 4 psi above the placard and recheck once the tires are cold.
Can I replace just one tire?
Sometimes, if the others have plenty of tread left. On many AWD vehicles, a large difference in tread depth between tires can strain the drivetrain, so the manual may require matching tread. Ask the tire shop to measure all four.
Key takeaways
- Check pressure monthly with the tires cold, using the door placard, not the sidewall number.
- TPMS warns only when a tire is about 25% low, so use a gauge.
- The penny test shows 2/32 inch; plan replacement around 4/32 inch for wet grip.
- Uneven wear points to pressure, alignment or suspension problems.
- Check the DOT date code; age matters as well as tread.
Look it up on CarManager
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General guidance, not professional advice. Intervals, specifications and legal requirements vary by vehicle, manufacturer and state: your owner’s manual, a qualified mechanic and your state agency come first. Costs mentioned are estimates. Our data sources.