Formulated to give you a harder faster ride the 99 Duro Formula Four Wheels from Spitfire feature unmatched flatspot resistance, smooth anti-stick slide, high rebound compound and are shaped to last longer. Tested by the Spitfire team, Formula Four are their best skateboard wheel yet. The 99D Conical Full Black Wheels are 52 mm and 54mm in diameter and a Conical Full shape. All our skateboard wheels are sold as a set of four.