Tire Tread Depth
The measurement of the vertical distance from the top of the tire tread rubber to the bottom of the tire's deepest grooves.
Tire tread depth is a critical safety measurement that indicates the wear status of a tire. The tread pattern is designed to channel water away from the contact patch, preventing hydroplaning and maintaining traction on wet, snowy, or muddy roads. Tread depth is measured in thirty-seconds of an inch (32nds) or millimeters.
New passenger car tires typically start with a tread depth of 10/32 to 12/32 of an inch. In the United States, a tire is legally worn out and unsafe when the tread depth reaches 2/32 of an inch. Most tires feature built-in 'wear bars' (tread wear indicators) that run across the tread grooves at this level, showing a flat bridge when the tire is worn out.
Driving with worn tires significantly increases stopping distances on wet roads and heightens the risk of punctures and blowouts. Mechanics use a tread depth gauge during inspections to advise drivers on when tires should be replaced or rotated to ensure safety.