Good to know. The Power Tap is perhaps the ideal power meter for this particular application. Both of the others whose CdA improved with power were riding road bikes with crank-based meters so I wondered whether we were picking up drive train losses. Power Taps, of course, don't have that issue.

If the analytical approach were less precise then drive train losses wouldn't even be on the radar screen but since the method is pretty sensitive I wondered about it. The other thing that's a kick is that as you speed up you start "catching your own draft." You can clearly see that in some of the hour record attempts where apparent CdA decreases a little until you reach equilibrium. Even a straw can stir a bath tub if you go around and around enough.