Which of the following is not one of the three main tread designs?

The answer is correct because the term "universal" is not recognized as one of the main tread designs in tire manufacturing. The three primary tread designs used in automotive tires are symmetrical, asymmetrical, and directional.

Symmetrical tread designs feature a uniform pattern across the entire tread, which provides versatile performance in various driving conditions. Asymmetrical tread designs have distinct inner and outer sides, optimizing different performance characteristics, such as improved handling and traction. Directional tread designs are designed to channel water away from the tire and provide enhanced grip in wet conditions, meaning they must be mounted in a specific orientation.

Understanding these tread design categories is crucial for selecting appropriate tires for specific driving needs and conditions. The "universal" option does not fit into these established categories and therefore is the correct choice here.