Skateboard wheels are usually made of polyurethane, a flexible rubber-like material. They are available in a range of hardness levels and sizes to meet the needs of different skaters. Enclosed ball-bearings in the wheels reduce friction for a smooth ride.
Skateboard wheels range from 48 to 85 millimeters in diameter and from 75 to 101 on the Shore durometer hardness scale. Higher numbers indicate harder wheels. Wheels in the 52- to 55-millimeter range with a hardness of 95 or higher work well for general purpose skateboarding. Larger, harder wheels are good for riding ramps and getting vertical height, while smaller, harder wheels facilitate technical tricks. Softer wheels are good for riding smoother on rough surfaces.