The Ultimate Wheel 54mm X 31mm Wide Set of Four wheels, contact 15.25mmX-Formula rolls over rough terrain like softer wheels do, but slides much like a harder wheel will. Speed: X-Formula™ is extremely fast because it has a super high rebound.X-Formula will slide when you ask it to, and grip when you need it mostdeveloped over a ten year period to optimise performance and fine tuned to perfection, It has been developed using the highest quality, longest lasting materials.Wheel Core NoneWheel Diameter 54mmWheel Width 31mmWheel Hardness 97aWheel Formula XFWheel Colour WhiteWheel Suggested Use StreetWheel Surface SmoothWheel Shape V6 Bones X-Formula V5 Sidecut X97A Skateboard Wheels Natural 54mm