Wheel Diameter = 56mm / Wheel Width = 32mm Durometer/Hardness = 84B = 104A | Increased Speed, Higher Rebound, and More Slide-Ability Wheel Shape = Shape: P5 Sidecut | Sidecut Walls Designed for More Stability, Less Drag, and Longer Grinds Wheel Ride Patch = 16mm Skatepark Formula (SPF) is very high quality urethane specifically formulated to resist flatspotting on slick or smooth surfaces while maintaining a higher rebound for a quicker response and a faster roll. Skatepark Formula has a high resistance to abrasion while not compromising hardness and slide ability. The amazing new X-Formula (XF) is another industry leading innovation from the BONES WHEELS factory. X-Formula rolls over rough terrain like softer wheels do, but slides much like a harder wheel will.