The wheel in back is just for training. It is pretty heavy, does not require any truing. I save my other set of wheels for racing. As far as aero dynamics I have not given it much thought. You see a lot ot TT bikes with disk on back and low spoke count front. I think this is a for both handeling and areo purposes. The front I am running is a 32h and tends to stay in true better than back wheels.