The penny test is the classic 30-second tread depth check. Take a penny, flip it upside down, push Lincoln’s head into a main tread groove. If the tread fully covers Lincoln’s head, you have more than 2/32″ of tread remaining. If you can see the top of Lincoln’s head, you’re at or below the legal minimum and you need to replace your tires now.
The penny test works. But it tests the wrong threshold for a safety-conscious driver. 2/32″ is the legal minimum — the depth at which it becomes illegal to drive on the tire in most states. It’s not the depth at which the tire is still safely usable. By the time the penny test fails, your wet-weather stopping distance is roughly double what it was when the tires were new.
This guide explains how to do the penny test correctly, what each result means, and why most drivers should swap to the quarter test instead.
Step by Step
- 1. Get a U.S. penny. Any year. The relevant measurement is the distance from the rim to the top of Lincoln’s head — approximately 2/32″ (1.5–1.6 mm).
- 2. Flip the penny upside down. Lincoln’s head should point into the tire when you insert it.
- 3. Insert into a main tread groove. Pick one of the deepest circumferential grooves — not a small sipe, not a wear indicator bar. Push the penny down until it stops, with Lincoln’s head going to the bottom of the groove.
- 4. Read the result. Look at how much of Lincoln’s head is visible above the tread.
What You Should See
- Tread fully covers Lincoln’s head and most of his face — You have more than 4/32″. The tire is still safely usable. You’re nowhere near the danger zone.
- You can see Lincoln’s hair but not the top of his head — You have around 3/32″–4/32″. Below the practical safety threshold, but still above the legal minimum. Start shopping.
- You can see the very top of Lincoln’s head — You’re at 2/32″ or below. Legal minimum hit. Replace now — you’re at the danger threshold for wet weather.
- You can see most of Lincoln’s head — You’re below 2/32″. Below the legal minimum. Replace immediately. Don’t drive in rain until you do.
Check Multiple Spots on Each Tire
One reading per tire isn’t enough. Tires don’t wear evenly. Test three points on each tire:
- Inside edge (closest to the engine)
- Center
- Outside edge
Take the worst reading as your actual depth — your tire is only as good as its weakest point. If the inside edge and outside edge differ by more than 2/32″ of tread, you have an alignment or suspension problem causing uneven wear, regardless of how much overall tread remains.
Why the Penny Test Is “Almost Too Late”
The penny tests at 2/32″ because that’s the legal minimum — the threshold most state laws and tire wear indicator bars use. But there’s a big gap between “legal” and “safe”:Tread Depth Wet Stopping Distance (70 mph) Compared to New 10/32″ (new) ~195 feet Baseline 4/32″ (safety threshold) ~290 feet ~50% longer 2/32″ (penny test fails here) ~380 feet ~95% longer (nearly double)
By the time the penny test fails, your tires have lost most of their wet-weather performance. The 90-foot difference in stopping distance between 4/32″ and 2/32″ is roughly six car lengths — the difference between stopping before an intersection and not. Hydroplaning risk also climbs sharply across the same range.
The practical implication: if you only use the penny test, you won’t get a warning until you’ve already been driving on dangerously thin tread for a long time.
Use a Quarter Instead
A quarter does the same test, but at the 4/32″ safety threshold instead of the 2/32″ legal minimum. Distance from the rim of a quarter to the top of Washington’s head is roughly 4/32″.
Procedure is identical: flip upside down, push into the tread groove, see whether Washington’s head is covered. If the tread covers his head, you’re safely above 4/32″. If you can see space above his head, you’re below 4/32″ and should start shopping — while you still have time to choose tires calmly instead of needing four by Friday.
The full quarter test guide walks through the procedure and the readings.
When the Penny Test Is the Right Tool
Two situations where the penny is still useful:
- You only have a penny. Better to check with a penny than not check at all. Just know that “passing” the penny test only means you’re not yet at the legal minimum — not that the tires are safe.
- You want to confirm the tire is illegal. If you’re documenting an unsafe tire for insurance, a tire-shop dispute, or a used-car purchase walk-away, the penny test gives you a clean visual confirmation that the tire is below the legal threshold.
Wear Indicator Bars Do the Same Thing
Every modern tire has small rubber strips molded across the tread grooves at exactly 2/32″ depth. When the tread is flush with these strips, you’re at the legal minimum — the same threshold the penny tests. Wear bars are convenient as a passive last-chance warning, but they’re set at the danger threshold, not the safe one.
Bottom Line
The penny test works correctly — it’s just measuring the wrong threshold for most drivers. Lincoln’s head covered means you’re above the legal minimum of 2/32″. Lincoln’s head visible means you’re at or below the legal minimum and your tires are now both illegal and dangerous.
If you want to know whether your tires are still safe, not just legal, use a quarter instead. Same procedure, same 30 seconds, but it triggers at the practical safety threshold — giving you time to shop for replacements before you’re driving on tread that’s already too thin.
