A front tire fails an inspection if the tread on two adjacent grooves is:

The correct answer revolves around the specific requirement for tread depth on front tires as mandated by safety regulations. A front tire will fail an inspection if the tread on two adjacent grooves is less than 3 millimeters (0.12 inches). This threshold is set to ensure that the tire maintains adequate traction and control, especially under adverse conditions such as rain or snow. When tire tread depth is insufficient, it can significantly affect the vehicle's handling, braking performance, and overall safety.

Having at least 3 millimeters of tread depth allows for effective water dispersion, which is critical in preventing hydroplaning and ensuring that the vehicle maintains grip on the road. Tires with deeper tread grooves are more capable of channeling water away, which helps reduce the risk of losing traction. Thus, any measurement below this standard indicates that the tire is no longer fit for safe operation, leading it to fail the inspection.

Understanding this requirement is essential for maintaining vehicle safety and compliance with regulations regarding tire conditions.