How do I check tire tread depth, and when are tires worn out?

Concerns & risks

Your tires are four years old and a shop that sells tires says you'll need new ones soon.

Causes & evidence

NHTSA's tire guidance says tires should be replaced when the tread wears down to 2/32 of an inch. Tires have built-in treadwear indicator bars molded into the grooves; when the tread is even with those bars, it's time to replace the tire. A quick penny test also works: put a penny upside down in a tread groove, and if you can see all of Lincoln's head, your tread is at or below 2/32 inch. NHTSA also recommends checking tires monthly for proper pressure, using the pressure on the placard inside the driver's door rather than the number on the tire sidewall, and looking for uneven wear, cracks, cuts, bulges or objects stuck in the tire. Uneven wear often points to alignment or pressure problems that will wear new tires too.

Edge cases: tires can need replacement because of age, damage or uneven wear even with tread left. Some states and drivers in snowy areas may want more tread than 2/32 inch for winter traction. Check your tire maker's age guidance too.

Checking just one spot on one tire misses uneven wear, which is often worst on the inside edge where you can't easily see it.

What to do

1. Park on level ground and turn the wheels to see the full tread.
2. Do the penny test in the inner, center and outer grooves of every tire.
3. Look for treadwear bars running across the grooves.
4. Check pressure cold, before driving, against the door placard.
5. Look for bulges, cracks, cuts and nails.
6. If wear is uneven, ask for an alignment and pressure check before buying new tires.

Common mistakes:

• Testing only the outer groove
• Inflating to the sidewall number
• Ignoring a sidewall bulge
• Replacing tires without fixing alignment

ReportSpeedMan tip: Also look up your tires on NHTSA's recall search using the tire identification number on the sidewall. Tire recalls are easy to miss.

What I would actually do

I'd penny-test every groove, check pressure cold, and buy tires when tread nears 2/32 inch or the wear bars, along with an alignment if wear is uneven.

The trade-off people miss: running tires to the legal limit saves money, but wet-road grip drops as tread wears, so I'd replace a bit early if I drive a lot in rain.

How to know it worked

Every groove passes the penny test and pressure matches the placard.

Quick FAQ

Is 2/32 inch the limit?
It's NHTSA's replacement point.

Can I just rotate them?
Rotation evens wear but doesn't add tread.

Where's the right pressure?
On the door placard.

Wrap-up: Replace at 2/32 inch, when tread meets the wear bars or Lincoln's head shows. Check every groove, pressure from the door placard, and look for damage.

Wiki: Vehicle Recalls and Fuel Economy Basics.

How do I check tire tread depth, and when are tires worn out: read the originals

• NHTSA: Tire safety
• NHTSA: Recalls lookup