Many non Tri riders scoff at concerns about aero penalty. However, I have played, experimented, and used aerobars on road and tri bikes since the mid-80's and know that I can drop to the aerobars and pickup 10% more speed. And, although aero penalty increases dramatically (exponentially?) with increase in speed, it is still very real, though not quite as intense, in the 15 mph range.
So, does a handlebar bag create an aero penalty? I've got to think it has to unless it is in the same vector as the riders legs and butt, thus creating no additional penalty.
Has this effect been tested and documented? Any unsubtantiated opinions?