Longboard, surfskate, and skateboard wheels are made from polyurethane. Depending on the intended use and desired riding characteristics, you can choose diameter, hardness, core position, lip shape, and color. The hardness of a wheel is determined using a Durometer Type A and ranges from 73a to 101a. 90% of all surfskate wheels are between 65-70mm in size and have a hardness of 75a - 85a.