Definition: A measure used to describe the hardness of inline skate wheels (and all kinds of other things.) The numbers go from 1 to 100. The higher the number, the harder. ... The word "durometer" comes from the name for a device used to measure hardness. ... You will find two numbers on your skate wheels. One is the wheel size, the other is the durometer rating. You can tell the durometer rating because it is the number with the "A" after it. ... Inline wheels are usually between 85A and 100A. Softer wheels wear down quicker but give better handling because they stick to the pavement better. Harder wheels last longer and roll faster.