Smaller wheels are used more for street or trick skating, while larger wheels are used more for recreational to speed skating. Small wheels turn accelerate more quickly. Large wheels are slower to accelerate but have greater high-end speed. Wheels range from 47mm for agressive street skating, to 60mm for children, to 72mm for recreational skating, to 80mm for racing. The durometer of a wheel can affect the performance, durability, shock absorption, and traction.
Soft wheels offer higher traction and the smoothest ride.
Hard wheels slide better, but have less shock absorption. The profile of a wheel's running surface can vary from a very pointed radius to a blunt, almost flat radius. A wheel profile should be selected for your skating style. Pointed or narrow radius wheels have less running surface, quicker steering and are faster, while wider radius profile wheels are more stable yet slower. It's made from a very hard plastic or urethane that bonds to the polyurethane tire.