When you purchase wheels, it is absolutely essential that you know for which purposes you want to use your board. Wheels are divided into classic wheels, which are made completely of polyurethane, and core wheels, which have an additional synthetic core inside.  The hardness grade of a wheel is indicated on a scale from 78A to 101A and 80B to 84B (e.g. 103A = 83B), and gives you information on the terrain on which the wheel rolls best. In other words: rough surface = soft wheels; smooth surface = hard wheels. Since the hardness grade cannot be exactly indicated above 101A, manufacturers such as Bones have their own scale. Bones wheels with the appendix STF (Street Tech Formula) are particularly suited for street –skating, because they have a very high flatspot resistance and a good slide-ability.  SPF, on the other hand, stands for Skate-Park Formula. These slightly harder wheels better transfer the speed on smooth surfaces such as bowls and mini-ramps, making them perfect for concrete.  Extremely soft wheels have established themselves with filmers, because these wheels minimize noise in the footage.

Skateboard wheels are usually available in sizes between 49 and 72 mm. The general rule is: larger wheels are better suited for higher speeds. Smaller wheels are suited for parks and for the street, because they are lighter and more compact. Additionally, some wheels are available in a special, slim version that reduces the friction while riding and sliding. These wheels are perfect for technical skating. On the other hand, they are not as stable during high speeds as wider basic wheels or a really wide versions.