What does "tread depth" refer to in tire service?

Tread depth specifically refers to the measurement of how deep the grooves in a tire's tread are. This measurement is crucial because it directly impacts a vehicle's traction, handling, and performance, especially in wet or slippery conditions. Adequate tread depth helps prevent hydroplaning and enhances grip on the road, which is essential for safe driving.

Tread depth is usually measured in millimeters and decreased tread depth can signify that a tire is worn out and may need replacement. Monitoring tread depth is an important part of tire maintenance to ensure safety and prolong the life of the tire. The other options relate to different tire characteristics but do not define what tread depth is.