I'm trying to understand why tennis balls have a higher bounce on clay courts than on hard courts. I understand that the amount of friction is greater on clay so as to slow the ball's vertical speed down and create a steeper angle of reflection. But I don't see how that explains why the coefficient of restitution is higher on clay (0.85) than on hard court (0.80). From what I understand, that means that a ball dropped on to a clay court will retain more of it's speed after the bounce (85 percent) than a ball dropped on to a hard court (80 percent). I understand why grass courts have the lowest coefficient of restitution (0.75). They are soft and so I suppose they 'withhold' more of the energy of the dropping ball. But aren't clay courts softer than hard courts? A ball dropping on a clay court sometimes even make a little 'dent' in the court surface, whereas hard courts (like Rebound Ace) should work precisely to re-bound the ball due to it's cement/rubber surface. No? Anyway, I hope someone is able to clarify this for me.