Are you considering purchasing a new pre-owned vehicle and need to know how much longer are the tires going to last? Are they legal?
How to measure tire tread depth
If this blog was in the U.K this part would be a piece of cake as tread depth is measured in mm. But no, not being metric it all gets a bit messy. Tread depth in the U.S is measured in 32nds of an inch. New tires usually come with 10/32″ depending on the type of tire. Trucks and SUVs may have deeper treads. The United States Dept. of Transportation (DOT) recommends replacing the tires when they get to 2/32″.
Wyoming law, “A person shall not operate any vehicle when one (1) or more of the tires in use on that vehicle is in unsafe operating condition or has a tread depth less than four thirty-seconds (4/32) inch in the case of tires which are used on the front wheels of a bus, truck or truck-tractor, or two thirty-seconds (2/32) inch in other cases, measured in any two (2) adjacent tread grooves at three (3) equally spaced intervals around the circumference of the tire but the measurements shall not be made at the location of any tread wear indicator, tie bar, hump or fillet. No vehicle shall be operated on any tire that has fabric exposed through the tread or sidewall” 1
What in the heck is a thirty second measurement anyway? Who knows (except mathematicians), but it’s not half a minute. Here is an easy way to check if the tires are legal and how much tread is left?
The Penny Test
- Take that penny that has been floating around your purse or pocket for the last few days and take it to your tires.
- Insert the penny between the tread ribs (raised parts of the tire).
- Turn the penny so Lincoln’s head is facing down into the tread
- If Lincoln’s head is not visible above the ribs then your tire tread is above 2/32″
- If you can see Lincoln’s entire head, it’s time for new tires!
Tread Wear Indicator Bars
Tires also have tread wear indicator bars (wear bars). These are located between the tread ribs and measure 2/32″. If the bars are flush with the ribs then it’s time for new tires.
Do you have any interesting stories about tire tread depth? Tired of Pennies? (Pun intended…sorry) Put one to good use.
Lauren has been working in the automotive industry both in the U.K and in the U.S. for over 10 years. A car geek, photographer, big game chaser and bagpipe player, powered by coffee. Send your questions to: