How to Check Tire Tread

Checking your tire tread takes thirty seconds and a single coin. Slide a penny into a groove with Lincoln upside down: if you can see the top of his head, the tire is at or below the 2/32-inch legal limit and needs replacing. A quarter gives you an earlier 4/32-inch warning. Here is the full method, plus how to read wear bars and spot uneven wear.

The penny test, step by step

The penny test is the classic no-tools check, and it works because the gap from a penny's edge to the top of Lincoln's head is almost exactly 2/32 of an inch — the legal wear limit.

• 1. Hold the penny with Lincoln's head pointing down into the tread and facing you.
• 2. Insert it into a groove of the tire, pushing it in as far as it goes.
• 3. Read it: if part of Lincoln's head stays covered, you have more than 2/32 inch of tread left. If you can see the very top of his head, the tire is worn out and must be replaced.
• 4. Repeat in several grooves across the tire and on all four tires, since wear is rarely even.

Read the built-in wear bars

Every modern tire has its own indicator built in. Look across the tread and you will see small raised rubber bridges sitting in the grooves, running perpendicular to the tread pattern — these are the wear bars, molded at exactly 2/32 inch. When the surrounding tread wears down until it is flush with these bars, the tire is finished. Wear bars are quicker than a coin once you know where to look, and they confirm what the penny test tells you.

Check for uneven wear — and fix the cause

Always test the inner, center, and outer grooves, because the pattern of wear reveals problems. Both edges worn but the center fine usually means the tires have been running underinflated; a worn center strip means overinflation. Wear on only one edge points to an alignment problem, and patchy, scalloped, or "cupped" wear suggests worn suspension parts or tires that were never rotated. Catching this early lets you correct tire pressure, get an alignment, or start rotating before the wear destroys an otherwise good tire.

When tread is low — what next

If your tread is at or near the limit, plan to replace soon — worn tires lengthen wet stopping distance dramatically and raise the risk of hydroplaning and blowouts. Our guide on when to replace tires covers age and damage as well as tread. To make tires last, keep them properly inflated — see how to check tire pressure — and rotate them on schedule with our tire rotation guide. Buying new ones? Learn to read the tire sidewall so you get the right size.

Frequently asked questions

What is the minimum legal tire tread depth?

In the United States the widely used legal minimum is 2/32 of an inch, which is exactly where the penny test fails, that is, when you can see the top of Lincoln's head in the groove. Many safety experts recommend replacing well before that, at 4/32 inch, because wet-weather grip and stopping distance fall off sharply once tread drops below that point. The 2/32 figure is the worn-out limit, not a target to aim for.

Does the penny test actually work?

Yes. The distance from the edge of a US penny to the top of Lincoln's head is about 2/32 of an inch, the legal wear limit, so if his head is visible the tire is finished. A quarter works the same way for an earlier warning at roughly 4/32 inch. A dedicated tread-depth gauge is more precise and cheap, but the coin tests are reliable enough to catch a worn tire and need nothing you do not already have.

What does uneven tire wear mean?

Uneven wear points to a specific problem. Wear only on both outer edges usually means chronic underinflation, while a worn center strip means overinflation. Wear on one edge only suggests an alignment issue (camber or toe), and patchy or cupped wear can mean worn suspension parts or tires that were never rotated. Finding it early through a tread check lets you fix the cause before it ruins the tire or the rest of the set.