Originally Posted by
asgelle
And why do you think the power you produce depends on the direction of gravity? Don't you think it might have more to do with W/CdA vs. W/kg?
No it's all about the gravity and weight. If you have ever witnessed a tractor pull the weight on the sled works in the same principle. The actual weight on the trailer does not change. It slides forward and higher and keeps increasing the drag /resistance until the power of the tractor cannot overcome it. It works the same on the way down.
You can do a simple test yourself with a back pack and something for ballast. Go out with 20-30lbs in the backpack and do some hills and note your results over your ride without the ballast.