Originally Posted by shane45
No sir, YOU are wrong. Somebody needs to beat you with a Newton stick.
Use cars for an example...torque is what gets a car up to top speed quickly - HORSEPOWER (energy) is what keeps that speed constant. Why do you think race cars are made as light as possible? Lower mass uses less energy (and fuel) to maintain a constant velocity. No different on bikes...
The fact that you indicate that "more weight is actually beneficial on downhill bikes" actually proves my (OK, Newton's) point. More weight means that the bike is not as prone to shifts in direction and absorbs and stabilizes a bumpy downhill ride because MORE MASS IS HARDER TO CHANGE DIRECTION (any direction - forward for example, ie. acceleration). Therefore, the heavier an object, the more energy is required to get that object to change direction, or to accelerate.
edit - OK, you and Lo Farkas have edited and amended your posts above to make mine nearly void.
Acceleration is not a change in direction. It is a change in velocity. Theoretically an object at a certain velocity will remain at a constant velocity absent any forces acting upon it.
When a bicycle is at a constant speed, its mass is irrelevant in terms of applied force needed to keep it at that constant speed. You need the power to overcome all of the resistive forces acting on said bicycle (friction from air, tire/ground, bearings...), not the inertia of the bicycle itself. When you are accelerating, a heavier bicycle will indeed require more applied force, but it will not require more force to maintain a constant velocity assuming that aerodynamics, bearings, and tires are equal on both bicycles. Lo Farkas is right.