A mechanic finds that a front tire is worn on the inside of the tread only. What is causing this problem?

When a front tire is worn solely on the inside of the tread, it indicates that the tire is leaning excessively inward at the top in relation to the bottom. This condition is known as negative camber. Negative camber causes the tire's inner edge to make more contact with the road surface as opposed to the outer edge, leading to increased wear on the inside of the tread.

A correct camber angle is crucial for even tire wear and optimal handling characteristics. When the camber is set too negative, the excessive tilt causes uneven distribution of the vehicle’s weight across the tire's tread, concentrating it on the inner edge. This results in accelerated wear on that section of the tire.

In contrast, other factors such as toe settings, positive camber, or improper air pressure have different impacts on tire wear patterns that do not typically lead to the specific wear pattern of excessive inner shoulder wear observed in this case. For instance, incorrect toe setting might contribute to premature tire wear as well, but the nature of the wear would manifest differently. Therefore, identifying and correcting excessive negative camber is key to resolving the issue of inward edge tire wear.