Close the windows and glass sunroof
Driving with the glass sunroof and windows open results in increased air resistance and raises fuel consumption.
See also:
BMW 7 Series Owners Manual
h4 {color:#800000}
h3 {color:#0033CC}
h2 {color:#008000}
h1 {color:#FF0000}
...
Remove attached parts following use
Remove unneeded auxiliary mirrors, roof or rear
luggage racks after use.
Attached parts on the vehicle impair the aerodynamics
and increase the fuel consumption. ...
After the ignition is switched off
The roof can still be operated for approx. 1 minute,
as long as no door has been opened. ...