99a Durometer–More speed and control on all surfaces. Unmatched flatspot resistance. Smooth, anti-stick ride. High-rebound compound.

Formula Four Urethane–Formula Four urethane is unlike any other. Unbeatable lasting performance Spitfire urethane. Fast as hell. Long lasting, abrasion resistance, smooth anti-slick slide with a controllable grip, guaranteed*.

Both in the streets and under high-speed stress tests in Spitfire's lab, Formula Four wheels retained more material, coned less and kept their original shapes and sizes longer than any other wheel.

High Rebound Compound