I've seen a number of posters mention that they are faster downhill (coasting) because of their heaviness.

Gravity is the same for any mass falling in a vacuum (right?), but there are many other factors and more physics going on in a downhill bike coast than gravity in a vacuum... acceleration, momentum, air resistance, road friction, etc...

Anyone with the physics knowledge can sort this one out? Basically two riders on exactly the same rigs, all conditions being equal coasting down a hill, the only difference being that one weighs twice as much as the other with comparable extra girth.

Starting from zero mph who will get off to the best start? Will the other one catch up or overtake somewhere down the hill? Who will get further up the next hill by just coasting?

cheers!