Tire tread: replace at 2/32 inch, and check it with the wear bars or a penny

Why the line is 2/32 inch

NHTSA’s tire page says to replace tires when the tread is worn down to 2/32 of an inch, and to check tread every month along with tire pressure. [S1]

The number is built into the tire. Federal standards FMVSS 109 and 119 require treadwear indicators molded into the tread at 2/32 inch. In a 1996 letter, NHTSA said it picked that depth because early studies showed a tire rapidly loses its traction at 2/32 inch. [S3]

NHTSA’s inspection guide for states, 49 CFR 570.9, uses the same number: tread on each tire not less than two thirty-seconds of an inch deep. The same 1996 letter explains that states, not NHTSA, enforce tire removal, and they can set a deeper minimum. [S3] [S4]

If your gauge reads in millimeters, convert before you enter it. No gauge? Skip the number and use the wear bars or a penny below.

Three ways to check

• Wear bars. NHTSA calls them treadwear indicators: raised sections that run between the tread. When the tread is worn down level with them, it’s time to replace the tire. USTMA puts it the same way: bars flush with the tread mean replace. [S1] [S5]
• Penny. Put a penny in a groove with Lincoln’s head upside down and facing you. NHTSA says if you can see the top of his head, replace the tires. USTMA says if part of the head is covered by tread, you’re good to go. [S1] [S5]
• Tread gauge. The federal inspection guide says vehicles other than passenger cars may need a tread gauge, and on heavy vehicles without indicators it calls for measuring with a gauge at the area of greatest wear. [S4]

Check more than one spot. The inspection guide looks at two neighboring major grooves at three places spaced about evenly around the tire. USTMA adds a monthly look for uneven wear, high and low areas and unusually smooth spots. Do it on every tire, and NHTSA’s winter tips add the spare. [S2] [S4] [S5]

Out of pennies? The U.S. Mint struck its last circulating penny on November 12, 2025, but the coin is still legal tender, so the ones already in jars and cup holders still work. The wear bars need no coin at all. [S7]

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Winter, heavy vehicles and local rules

NHTSA’s winter tips ask for tread of at least 2/32 inch on all tires, a look at the sidewalls for cuts, punctures, bulges, scrapes, cracks and bumps, and a check before long road trips. NHTSA also suggests considering snow tires. [S2]

Some rules go deeper than 2/32. Colorado’s Department of Transportation says winter, all-weather and mud and snow tires meet its Traction Law only with at least 3/16 inch of tread, which is 6/32. That applies when the law is called. For vehicles over 10,000 lb, the federal inspection guide asks for 4/32 inch on each front tire (trailers aside) and 2/32 on the rest. [S4] [S6]

For your own state’s inspection or traction rules, check its official transportation or motor vehicle site. States set and enforce them. [S3]

Tread isn’t the only clock

Plenty of tread doesn’t make an old tire new. NHTSA says some vehicle and tire makers recommend replacing tires that are six to 10 years old regardless of treadwear. The last four digits of the Tire Identification Number give the week and year it was made, so 0308 means the third week of 2008, and that number may be on only one side. [S1]

NHTSA also says not to use the spare as a replacement for worn tires. Rotation helps wear stay even: USTMA says to follow your owner’s manual, or rotate every 5,000 to 8,000 miles if it gives no interval. [S1] [S5]

The monthly tire check

Do the tread with the pressure check. Our tire pressure guide covers where the right number lives and why to check cold. [S1] [S2]

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