When are tires considered to be worn out?

Tires are considered worn out when the tread depth is less than 2/32 of an inch. This specific measurement is critical because tire tread is essential for maintaining proper traction, especially in wet or slippery conditions. When the tread wears down to this minimal depth, the tires can significantly impair the vehicle's ability to grip the road, which can lead to an increased risk of hydroplaning and reduced stopping distance. Therefore, the 2/32 of an inch mark serves as an industry standard for determining when tires are no longer safe for use.

The other options, while they may signal issues with the tires, do not directly indicate that they are worn out in terms of tread depth. Visible cracks on the sidewalls can be a sign of degradation or aging and could lead to tire failure, but they don't specifically pertain to tread wear. Tires being over six years old could also raise concerns about their integrity, but age alone isn't a definitive measure of tread wear. Lastly, low air pressure is a performance issue that affects handling and tire wear but does not directly indicate that the tread itself is worn out.