What does a tire tread depth gauge measure?

A tire tread depth gauge specifically measures the depth of the tread on a tire. This measurement is critical because adequate tread depth is essential for maintaining traction, especially in wet or slippery conditions. When tires are worn down and the tread depth is insufficient, it can lead to reduced performance in terms of grip and an increased risk of hydroplaning. Regularly checking the tread depth with a gauge helps ensure that tires are safe for driving and comply with legal requirements.

The other options focus on different aspects of tire maintenance: air pressure is measured using a tire pressure gauge, width pertains to the tire's dimensions rather than tread depth, and alignment refers to the angle of the tires relative to the vehicle and the road, which affects steering and tire wear, but is not measured by a tread depth gauge.