Radar Bullet Neon Purple Skate Wheels 93A Hardness and the Shark Hub with DerbyThane Size 59mm x 38mm Roller Derby Speed Skating Replacement Wheels by Riedell - Combining both of Radar Wheels" newest breakthroughs, the Shark Hub and DerbyThane tire compound, Radar Wheels is proud to introduce the Radar Bullet. The Radar Bullet is a uniquely responsive, agile, and ultralight 59mm Roller Derby wheel designed for aggressive, top level game play. - THE SHARK HUB - Radar Wheels introduces the Shark Hub. Designed with convex fins that provide stiffness to the outer edge of the wheel and allow the wheel"s tire to perform at its optimal level. Traditional hubs with square or concave designs flex and limit urethane performance, resulting in slow and sludgy wheels. The Shark hub provides superior roll (speed), and balanced support from the outside through the middle and inside edge of the wheel. Shark Hubs are made in the USA with superior grade urethane which creates an intense bond with urethane tires. It is the finest, ultralight synthetic hub available. DERBY THANE - DerbyThane is a high performance urethane designed specifically for the wide variety of surfaces used in the world of Roller Derby. From concrete to wood to tile court to banked track surfaces, DerbyThane fills the need for nearly every derby skater.