Spitfire's Formula Four Urethane wheels are the ultimate skateboarders wheel. Made to keep their shape and size for longer, these wheels lessen the chances of flat spots and retain more material. The 99duro wheels offer better performance on rough street surfaces compared to the harder 101duro styles. This conical full wheel shape features a wider riding surface for lasting speed and extra control helping you lock into rails and ledges. Great for riding street or transition.