Roller skate wheels are defined by diameter (size) and durometer (hardness). But elasticity is the most underrated characteristic.
Many skaters believe that roller skate wheels only differ in size and hardness. However, other less commonly cited characteristics can significantly impact a wheel’s performance.
The hardness of the wheels is measured by the Shore Durometer. Measured as the depth of an indentation in the material created by a given force on a standardized presser foot. The Shore A scale is commonly used, measuring the hardness of flexible mold rubbers and elastomers. This ranges from very soft and flexible to hard with almost no flexibility at all. Some harder indoor wheels are specified using the Shore D scale, which measures the hardness of harder elastomers, semi-rigid plastics, and hard plastics. In practice, there is some overlap between these two scales.
Most wheels are made from polyurethane (PU), an organic polymer and versatile elastic plastic material. Besides hardness, PU can have a range of other attributes, including:
- Load-bearing capacity
- Flexibility
- Abrasion & impact resistance
- Resiliency
- Bonding capability to the core
Not all of these parameters are equally important for roller skating. However, for outdoor skating over rough asphalt, flexibility and resilience are crucial. The wheels must recover quickly from distortion when hitting edges or stones and unload the pressure. Otherwise, the wheels can get stuck. Even micro-movements can make a perceptible difference, as the fast sequence of distortion and unloading impacts performance.
The differences can be significant. I worked in a skate shop for several years and used two small PU balls, each with a hardness of 78A, to show customers the impact. One ball bounced like crazy when dropped on the floor, while the other barely bounced a quarter of an inch and stayed on the ground.
Elasticity is more important for smooth outdoor skating than diameter. Larger diameter wheels mainly provide a “better roll,” meaning longer distances with one stride, resulting in faster speeds. However, the angle between the surface and the tangent line of the wheels, which determines if the wheel will strike an obstacle at an acute or obtuse angle, is not significantly lower for 65 mm diameter wheels compared to 62 mm or even 57 mm diameter wheels. This difference cannot outweigh the lack of elasticity. High-rebound 57 mm diameter wheels will perform better than less elastic 62 mm or 65 mm wheels. Similarly, resilient 85A wheels will outpace less elastic 78A wheels.
If you want to skate effortlessly like a pro on the beach boardwalk or through city streets, choose wheels with higher elasticity that allow for a quicker “take off” when they stick at an edge. While 57 mm wheels can be a bit bumpy, 62 mm diameter wheels are often the better choice.