The Penny Test Is a Floor, Not a Goal: When to Really Replace Tires
By Rhino Tire USA Wholesale Team · Updated 2026-08-22
The penny test flags the 2/32-inch legal minimum — but wet braking and hydroplaning resistance degrade dramatically below 4/32, which is where the quarter test comes in. Treat 2/32 as the law's floor and 4/32 as your shopping trigger.
Two coins, two thresholds
- Penny test (2/32"): Lincoln's head upside down in the groove. See the top of his head → the tire is legally worn out.
- Quarter test (4/32"): same move with Washington. See his head → wet-weather margin is thin; start shopping.
Test multiple grooves across the tire — uneven wear hides in the shoulders. Or measure once with a $2 depth gauge and use the tread depth guide to see exactly how much usable tread you have left.
Why 4/32 is the real line
Independent wet-braking tests show stopping distances growing dramatically in the last few 32nds — grooves that can't evacuate water plane on top of it. Legal ≠ safe in rain.
The reference numbers
| Depth | Meaning |
|---|---|
| 10–12/32" | typical new highway tire (AT/MT: 13–17) |
| 6/32"+ | healthy |
| 4/32" | wet performance falling off — FMCSA steer-tire minimum |
| 2/32" | legal floor — wear bars flush |
Tread isn't the only clock
Trailer tires usually age out before they wear out — check the DOT date code too. Worn out? Find installation near you or browse tires.
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