All-Terrain Formula (ATF) wheels are poured in a special soft urethane we call All-Terrain Formula or (ATF). ATF wheels are excellent for rougher terrain so regardless of road quality, this revolutionary formula will roll you there quickly and smoothly. Features: Diameter: 56mm Durometer: 80a Width: 40mm Formula : All-Terrain Formula (ATF) Wheel Surface: Smooth Wheel Shape: Core