Originally Posted by JoeUser
My brother is into physics and here's what bothers me about it: Physics is supposed to be a way of explaining why things are the way they are. However, it is usually (as in this case) a very roundabout way to nowhere. In your attempt to explain why this weird phenomenon is happening you forget the simple truth: IT DOES.
Heavy riders go down hills faster. They do. There's nothing you can do about it.
Of course science starts with what's observed (although a lot of times people forget that. People used to assume all heavy objects fell faster than light objects, ignoring observation).
Nevertheless, understanding the science can help you achieve things you wouldn't otherwise, and avoid mistakes based on faulty assumptions. You can go faster downhill by adding weight or by adopting the most aerodynamic position. Weight works better, but it penalizes you too much when you try to go uphill.