Classic Throwback Edition Formula Four Wheels. Spitfire Formula 4 features more speed and control on all surfaces, unmatched flatspot resistance, smooth anti-stick slide, high rebound compound. 100% true performance urethane. The Spitfire Classic is the #1 wheel shape in skateboarding. medium riding width surface with round sidewalls. Designed for control in all situations. 66.6mm x 41.3mm 99A.