Hardness of longboard wheel

The hardness of longboard wheels varies and is made of polyurethane. Hardness of polyurethane is determined by a wheel's durometer. Durometer is important for wheel performance because it determines how well it grips the ground. Higher durometers will be more 'slidey' than lower durometers, as lower durometers will be more 'grippy'. There are 75a-100a wheels available for longboards/skates. Standard skateboard wheels have a harder durometer of 75a-90a, while longboard wheels have a softer durometer of 75a-90a. For more grippy wheels, you'll find 75-78a, while freeride and downhill wheels feature 80-90a, and slide wheels feature 80a and higher. Is there a meaning behind that 'a'? Generally, durometer ratings start with an 'a'. Each polyurethane, rubber, and plastic has a different hardness rating (A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, R). Our explanations of scale differences will not be based on molecular science. In addition to 'a' skateboard wheels, some longboard and skateboard wheels have 'b' scale ratings. This is because of the type of urethane used.