Spitfire is proud to introduce their newest shape to those who keep the underground lit with theSpitfire Formula 4 Tablet 101aWheels. Formula Four Performance Urethane lasts longer, withstands more abuse and performs superior to all other wheels. Designed to combine all the desired properties of a performance wheel without sacrificing any one attribute at the expense of another. Features: Size: 54mm Durometer: 101a Straight cut profile Thinner riding surface Unmatched flatspot resistance Smooth anti-stick slide High rebound compound 100% true performance urethane Holds shape longer