And recreational or fitness skaters, will also be in the 72 to 76 millimeter size but with an even more rounded wheel. Racing wheels are usually about 76 to 80 mm and have narrower profiles. A wheel's hardness is expressed in terms of a durometer number. The softer the wheel, the lower the number. The harder the wheel, the higher the number.
Soft wheels have a more comfortable ride, grip the surface better but tend to wear out sooner.
A harder wheel has a rougher ride, doesn't hold the surface as well and will last longer. They're slow, noisy and inexpensive. The higher the number, the higher the precision. ABEC 1 and 3 are the most popular and are found in most fitness and recreational skates. Remember, as the rating goes up, so does price.