The #1 shape in skateboarding worldwide, the Classic is proven for speed, slide and control. 101a Duro, for a harder, faster ride. Proven formula four performance made in Spitfire's hardest duro for extra speed and slide. Spitfire Formula Fours were developed to combine all the desired properties of a performance skateboarding wheel without sacrificing any one attribute at the expense of another. The Formula Four Performance Urethane comes not from a single benefit, but from a combination of qualities and features that together produce a truly great wheel. An unmatched abrasion resistant wheel, meaning fewer flat spots and a longer lasting wheel that holds size and shape longer. Spitfires are top of their class. One of, if not THE best skateboard wheel out there.