The big hole where the ice chest and lawn chairs go upsets the
airflow.  Roger's California had the cowling the eliminated that hole
and it was noticeably cleaner. The luggage rack causes the boundary
layer to separate immediately behind it and become turbulent.  That
increases drag.

http://www.thesamba.com/vw/forum/viewtopic.php?t=316411&highlight=drag

Jim

On Jan 20, 2010, at 10:31 AM, Dave Mcneely wrote:

> Granted that common sense fails often on many fronts.  But I'd like to
> know, if indeed it is the case, how the vehicle with a pop top but no
> luggage rack would be more aerodynamic than the more typical
> camper.  If
> the airflow is smoother over that top, I'd be surprised.  But I've
> been
> surprised before.  In this case, I'd just like an explanation, so I'd
> understand better.  David