The #1 shape in skateboarding worldwide, the Classic is proven for speed, slide and control. 99a Duro is made for speed and lasting control on all surfaces. One of the most ridden duros worldwide. 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.