Was out in the our BMW 323 CIC yesterday with the top down My wife noticed driving at 80 km/hr( 50 mph) the BWM was quieter then the Prius was with the sunroof open The noise of sunroof is about my only pet peeve I have with Prius beside the colour of the radio and HVAC read outs
I don't know how quiet your bmw is, but I found that 1/4 or 3/4 is pretty quiet... if you open it fully, you can crack the two back windows about 3 inches and that then quietens it up too.
I think , I have been spoiled by the sunroof in my pick up truck, it is one that slides into the roof We had a '98 Grand Prix whose sunroof slide on top of the roof, it was also noisy I will have get my sound meter out and take some measurement of the truck and Prius The only problem is the wife left today to go take care of the grandkids for 6 weeks, I will miss her, and also miss the wife( thank God she does not visit this forum LOL)
I have a Subaru Outback with a sunroof that slides into the roof to open as well. It is NOISER than the one in my Prius when both are fully opened so I think it just depends on each vehicle. In the truck with the air basically hitting a wall, much more of the air may be forced up higher due to the flattened angle (more toward 90 degrees) than the sleeker more aerodynamic Prius and BMW windshield slopes. So maybe this is why. Who knows (well, I guess some engineers!). I only drive around town with the sunroof open anyway. In any vehicle at highway speeds and certainly freeway speeds, the drag is gonna be much greater with the windows and sunroof opened. The faster you go, its not a linear relationship, the drag becomes a much, much bigger player.
Yea, I'm not sure how air drag works.... seems if it created turbulence inside, that would be a drag and if not, that would mean the normal airfoil of the car must be going over the sunroof making it "invisible" so to speak. But I would think when there is turbulence inside, the airfoil is getting "interrupted" by the large hole in the top. Nevertheless.. seem the way the prius opens, the air foil is simply changed to a higher point than when closed due to the prominent blade that sticks out in front. That alone would lessen the aerodynamics of the cars "simulating a taller car" thus cutting a larger hole through the air.. but I honestly haven't seen a mpg hit that I can detect... regardless of what speeds I go.... I'm sure there is one, but it appears to be very negligible.
if just the sunroof is open, i hear NOTHING...but not saying my hearing is great...my SO complains i have everything turned up too loud. but if i open the back windows a smidgen, i do start to hear wind noise but its pretty low key. but one thing i do notice immediately, the road noise is louder, the traffic sounds, etc. might be tough to sort one from another with all that coming at you at once
