Tire Tread Penny Test: How to Do It Correctly (and What It Really Tells You)

2026-01-09•By TireCheck Team

Tire Tread Penny Test: How to Do It Correctly (and What It Really Tells You)

The “penny test” is one of the fastest ways to estimate whether your tire tread is dangerously worn. But many people do it wrong, misread it, or assume it measures “grip” directly. It doesn’t. It is a quick proxy for remaining tread depth, which strongly affects wet traction and hydroplaning resistance.

This guide explains how to perform the penny test correctly, how to interpret the result, and when you should use a tread depth gauge instead.

What the Penny Test Measures

The penny test is designed around a key threshold: 2/32 inch (1.6 mm). In the U.S., that is commonly treated as the minimum legal tread depth for passenger tires. When tread approaches this level, the grooves are too shallow to evacuate water effectively, raising hydroplaning risk and extending wet braking distances.

Important: tread depth is not the only factor for traction (rubber compound, temperature, road texture, inflation pressure, and alignment also matter). But tread depth is the easiest safety-critical variable for everyday drivers to check.

How to Do the Penny Test (Correct Method)

1.Park on a level surface, set the parking brake, and turn the steering wheel for access if needed.

2.Pick a main tread groove (the wide grooves that run around the tire).

3.Insert a U.S. penny with Lincoln’s head down into the groove.

4.Look at how much of Lincoln’s head is visible.

If the top of Lincoln’s head is fully visible, you’re likely at or below 2/32 inch and the tire should be replaced as soon as possible.

Where to Measure (Don’t Skip This)

Tires don’t always wear evenly. You’ll get a more accurate picture if you check:

•at least 3 points across the tread (inner, center, outer)

•at least 2 locations around the circumference (front and back of the tire)

If one shoulder is much lower than the rest, that can indicate alignment or suspension issues, even if the tire “passes” in the center.

Common Penny Test Mistakes

•Checking only one groove: you can miss uneven wear and cupping.

•Measuring on a worn edge block: always use a main groove for consistency.

•Confusing “legal” with “safe”: 2/32" might be legal, but it’s often not ideal for rain.

•Using the test on winter driving: snow traction typically requires more tread depth than the minimum legal threshold.

Does the Penny Test Measure Friction?

Not directly. Friction (traction) depends on rubber compound, temperature, and the microscopic texture of the road. Tread depth mainly helps the tire manage water. In wet conditions, traction often fails because water builds a film under the tire, reducing direct rubber-to-road contact. Deeper grooves help channel water away, delaying hydroplaning and improving wet braking.

If you want a more precise measurement than a coin, use a gauge:

•Read: How to Measure Tire Tread Depth (Gauge Method)

•Read: Minimum Tire Tread Depth: Legal vs Safe