The "duckbill" on most of today's motorcycle helmets (assuming this is for venting?) has always bugged me. I have heard that it is not an aero penalty but it sure looks like it. I was looking through a few of the A2 videos and the AGV helmet with a more forward facing rider (rider looking forward vs. down at the tank) seemed to be the smoothest shape. The AGV does not have a "duckbill" but does have a swept rear shape like the bicyclists use, though not as pronounced and thankfully without the spandex.
A traditional style helmet with a more round shape would seem to me to be the worst aero shape. The AGV looks best, and the duckbills - ?
Which style would work best with street style bodywork e.g. not a streamliner or fishtail bodywork.