Wheels are the most often changed part in every skate. Inline wheels have different profile, construction of the hub, they are made from different material and are specially designed for different kinds of skating. Every inline wheel has its own hardness ("A" rate) and size (diameter in mm). Harder wheels (higher "A" parameter) will be more durable but they will have less grip. Choosing right wheel will have a big impact on the comfort and safety of skating.