Quick answer: put a penny upside down into the tread groove, with Lincoln’s head facing you. If you can see the top of his head, the tread is at or below 2/32 of an inch, the legal minimum in most US states, and the tire needs replacing. For better grip in wet or snowy weather, many experts recommend replacing tires at 4/32 inch. You can check that with a quarter.
Key Takeaways
- The legal minimum in most US states is 2/32 inch. In the UK it is 1.6 mm across the central three-quarters of the tread.
- Grip on wet roads drops noticeably long before tires reach the legal limit.
- Check several points across and around each tire, because uneven wear is common.
Method 1: The Penny Test
- Hold a penny with Lincoln’s head upside down and facing you.
- Push it into one of the main tread grooves.
- If you can see the top of Lincoln’s head, the tread is 2/32 inch or less: replace the tire.
- Repeat at several points around the tire and across the inner, middle and outer grooves.
Method 2: The Quarter Test
Use a quarter the same way, with Washington’s head upside down. If the tread does not reach his hairline, the tread is about 4/32 inch or less. The tire is still legal, but you should start planning to replace it, especially before winter.
Method 3: A Tread Depth Gauge
A tread depth gauge costs only a few dollars and gives an exact reading. Push the probe into the groove, press the base flat against the tread and read the measurement. Take readings on the inner, center and outer grooves of every tire.
Method 4: Tread Wear Indicator Bars
Most tires have small raised bars molded into the bottom of the grooves at 2/32 inch. When the tread wears down flush with these bars, the tire has reached the legal limit and must be replaced.
What Uneven Wear Tells You
- Worn in the center: usually over-inflation.
- Worn on both edges: usually under-inflation.
- Worn on one edge: often a wheel alignment problem.
- Patchy or cupped wear: possible suspension or wheel balance problems.
If you see uneven wear, have the alignment and suspension checked. Otherwise new tires will wear the same way.
Frequently Asked Questions
How often should I check tire tread depth?
About once a month, when you check tire pressure, and before any long trip or the start of winter.
Is 4/32 tread depth safe?
It is legal, but wet and snow grip are noticeably reduced at this depth. Many drivers replace tires at 4/32 inch, especially before winter.
How much tread does a new tire have?
Most new passenger car tires start with about 10/32 to 11/32 inch of tread. Truck, SUV and winter tires often have more.
Should I replace all four tires at once?
Ideally, replace them in pairs on the same axle. If you replace only two, most tire makers recommend fitting the new tires on the rear axle for better stability. All-wheel-drive cars may need all four replaced together, so check your owner’s manual.
