Tread Wear Indicator
Raised bars molded into the main grooves of a tire tread to show when the tire is worn down to the legal limit.
Tread wear indicators (also known as wear bars) are small, raised rubber bars molded into the main longitudinal grooves of a tire tread. They are positioned at a height of exactly 2/32 of an inch (1.6 mm) above the bottom of the tread groove, which is the legally defined limit for safe tire wear in most jurisdictions.
As the tire tread wears down from driving, the depth of the grooves decreases. When the tread wears level with the wear bars, the indicators appear as solid rubber bridges running across the tread pattern, indicating that the tire has reached the end of its useful life. Driving on tires worn to the wear bars significantly increases the risk of hydroplaning, punctures, and loss of wet-weather traction.
Mechanics inspect wear bars during routine service to advise drivers on tire replacement. If a tire exhibits uneven wear (for example, the wear bars are showing on the outer edge but not the inner edge), it indicates an alignment issue or improper tire inflation, which should be corrected to prevent premature tire failure.