Formula Four Classic Shaped WheelGet a fresh spin on Spitfire's classic look and feel with the Spitfire Formula Four Classic Black & White 54mm 99a Skateboard Wheels. These wheels come with Spitfire's flat spot resistant urethane formula to ensure an optimal ride from start to finish, a 99a urethane hardness rating provides a predictable feel from gripping vert to ripping powerslides. Formula Four Classic Black & White 54mm 99a Skateboard Wheels by Spitfire. Spitfire's Formula Four