Ricta Wheel Dynamics John Shanahan Geo Naturals Pro Wheels in 53mm Round shape with Ricta's 101a high performance urethane for maximum speed, smooth roll, and fewer flat spots. Wheel Diameter (Millimeters) 53.1 Wheel Durometer/Hardness 101a Road Surface (Millimeters) 16.75 Wheel Shape Round Wheel Width (Millimeters) 33 Ricta Geo Naturals Shanahan Round 101a Skateboard Wheels - 53mm