The durometer, or “duro,” refers to the hardness of the urethane. Duro is used to measure wheels, bushings and some risers, and is an internationally recognized scale for all materials. A softer material will be paired with a lower number, while a harder material will be paired with a higher number. Most longboard wheels fall between 75a and 90a.
Soft wheels are typically more grippy and smooth-rolling over road inconsistencies. Hard wheels, on the other hand, will usually slide more easily and generally roll quickly over smoother surfaces.
However, it is a common misconception that the durometer is the sole determining factor in the durability, slide and grip characteristics of a wheel. While durometer does affect these features, it does not directly reflect the rebound, lifespan, or slide characteristics of the wheel and its urethane.