Originally Posted by
AlmostTrick
Of course weight matters even on the flats... it doesn't keep moving all by itself without any input from the rider.
Try this exaggerated test: Pull an enclosed trailer while empty. (enclosed to maintain the same aerodynamics) Use an electric motor to get up to X speed. (to eliminate acceleration) Accurately measure speed and power output over a flat course.
Then repeat while adding weight inside the trailer. If weight really doesn't matter like some here are saying, you should be able to keep piling it on (hundreds of pounds!) and see no increase in power needed. Does anyone here really think that would happen?
Yes, as long as air resistance and rolling resistance would remain the same, it would indeed happen. Unfortunately, rolling resistance grows with added weight, as there are no absolutely hard wheels and roads in the real world. This is why railroads are the most effective means of transport over land: it takes quite a while for the locomotive to get the whole train rolling, but once it's moving, it is able to pull the thousands of tons quite easily, since the deflection in steel wheels and tracks is minimal.