The essential criteria in choosing skateboard wheels are diameter and hardness. The diameter is expressed in mm. The "small diameters" (49 to 51 mm) are intended for the practice of very technical street. The "classic diameters" (52 to 55 mm) are intended for versatile skaters practicing the street and rolling a lot of spots in spots ... The "large diameters" (over 55 mm) are intended for pool riders, ramps and big parks. The hardness of a skateboard wheel is expressed in shore (A). The "soft" wheels (78A / 80A) are generally intended for longboards and cruisers for riding. The "semi soft" or "semi hard" wheels (92A / 98A) are intended for riders who do tricks but are looking for a certain grip or practicing on very damaged ground. The "hard" wheels (99A / 101A) are the ultimate street skating wheels.