I understand the inefficiency of shaft drive,....its not the shaft, but the gears that involved w/ it. We're talking a gearbox here, in which we have friction from not only the gears meshing together having to squeeze the oil out, but all the bearings involved, which also have resistence from the oil they run in.
Now here is what really surprised me,.... years ago already. Why are the most efficient cars all front wheel drive ? Supposedly its because all the shafts and gears are turning inline or parallel w/ each other. Supposedly anytime the power turns a 90 deg corner,...such as a ring and pinion,... such as in a shaft drive motorcycle, more power is lost than if the shafts are all turning in the same "plane".....is that the right word?
If that is all true, I really don't understand that.
On edit,
Sorry, the above post says most of it all. It wadn't there when I left