Weight reduction - not always good?

[JanGeo]

Yeah you need enough weight to maintain a coast downhill without stopping thus NOT using the engine at all and that alone give the greatest efficency since you don't run the engine. Getting up the hill doesn't matter as much so it comes down to the hills that you have to deal with. Now if you have steep hills then less weight would be better since you have sufficent mass to maintain downhill speed. You also have to factor in the aero drag with the weight so you don't have to run the engine to get down a hill.