Wheel Durometers are pretty straight forward but always worth a talk about what is really going on. We will cover this topic more in the future but for now here is an excerpt from Bones wheels about the basics. This is a huge topic in the world of urethanes and only a small portion of it is covered here as it applies to skateboard wheels.
What Bones has to say:
Shore Durometer A Scale is good, but does not cover the entire range of skate wheel hardness and is very limited because the scale goes from 1 to 100 and anything over A 95A does not compute accurately.
Shore Durometer B Scale is perfect for skate wheels because:
- It is very similar to the A Scale, but reads 20 points lower, allowing the useful scale to be extended by 20 points, which covers the entire hardness range of skate wheels in one scale. It uses the same soft spring as the A Gauge, but the conical gauge needle of the D Scale.
- Because the spring is soft, the B Scale gauge needle does not puncture the skin of the wheel surface, resulting in the same reliable reading as the A Scale does.
Shore Durometer D Scale is designed for hard rubbers and rock hard urethanes, not soft, bouncy urethanes that are used in skate wheels. It has a very stiff spring behind its sharp conical needle and often punctures the skin of the wheel being measured, this resulting in 5-10 points softer reading than is correct. Thus, Shore D Scale should not be used for wheels in the useful skate wheel range.