This procedural material was designed to tell a story about where this airplane has been. Authored in Substance Designer, parameters for tread pattern, wear marks, glossiness, and dirt/mud were embedded into the material for storytelling capability.
Take note that dirt and mud gathers in the tread cavities of the tire, but when the tread pattern is worn away, dirt gathers more broadly across the tire material. Also, if the dirt is cranked up high enough, the entire tire is covered with mud anyway - but with with the cavities being especially filled with dirt.
The tires are mounted onto the landing gear for a PBY-5A Catalina, an amphibious airplane from World War 2 that hunted submarines. The aircraft has a reputation for being able to operate anywhere in the world; from the international airports, the middle of the ocean, dirt runways in forests, and even landing and taking off from ice sheets in the north pole.
Two different tread patterns were required because the front and rear landing gear tread is different - the front being used to steer the plane when taxiing on a flightline, the rear simply for grip when braking.
The landing gear is just one part of an entire CG recreation of the historical PBY-5A Catalina aircraft. The aircraft is the flying home of two men traveling Europe after WW2, trying to put the pieces of their lives together after the most devastating war the human race has ever seen.
To read more about this ongoing project, check out this blog post.