Wind Deflectors?

[Grommit]

Hi All,

There's a very noticeable "drumming" effect when I open any of the windows at anything above about 40MPH. I know the X5 isn't the most aerodynamic of cars, but I wasn't expecting it to be that bad. Any way, I want to fit some wind deflectors to try and get rid of, or at least reduce the racket. There appear to be 2 types, "In Channel" & "Stick on" I don't really like the idea of stick on ones, but they claim that the in channel ones cause problems with the windows.
So, has any one any experience of these things? Any idea which are the best, or if they even work? Any advice much appreciated.  Thanks

[jaynana]

don't think the effect has anything to do with how aerodynamic the car is...

Cd on the E53 is .35 btw..  didn't ever think the X was exceptionally aerodynamic, but then a Cd of .35, not bad compared to even the Porsche 997 GT2 has a Cd of .32!

[rhinoman]

Ours had wind deflectors on when we bought it and with the windows up they gave a slight noise, quiter without them now. I don't think the windows down benefit out weighs the windows up noise.

[X5Sport]

You can reduce the buffet by opening one of the rear windows just a crack.  It worked on mine.  You get the same thing with the roof if it's fully retracted.

Given the car has climate control which ideally should be running all/most of the time* I don't suppose BMW gave much thought to those who travel 'au naturelle'.



*AC compressor needs to be used regularly to avoid seal failures.

[snipez999]

Just invite 535d boy round. He'll reduce the buffet in seconds (and thirds)

[Grommit]

Pretty sure it has everything to do with aerodynamics Jayana   Given that there is no drumming when the car is stationary and it increases with speed, until at about 60 mph the vibrations actually hurt your ear drums.
You are talking about Coefficient of Drag, which is how "slippery" it is and is just one small aspect of aerodynamics.
Surely I cannot be the first person to experience this phenomenon, it must be common unless I've got a strangely unique car. Does everyone else just live with it?

[jaynana]

huh?

u said

[quote="Grommit"]
I know the X5 isn't the most aerodynamic of cars, but I wasn't expecting it to be that bad.
[/quote]

isn't Cd exactly that? measuring how good or bad the aerodynamics of the car is?  :hmmm: 

[Reusch]

Yep Grommit it's shocking one of the many flaws with the x5.

[Finglonga]

[quote="X5Sport"]
You can reduce the buffet by opening one of the rear windows just a crack.


[/quote]

This exactly, with the rear windows down 4" the front ones can be fully down with zero buffeting (on the X6 at least), so try that before spending money on deflectors.

[Grommit]

Thanks for the replies guys, I was beginning to get a bit paranoid.

Jaynana

C.D. is an aerodynamic property, but it is only one small area that measures the resistance of the vehicle to movement through the air and compares it with that of a similarly sized block.
The drumming I am on about is caused by rapid fluctuations of air pressure inside the car when the windows are open and the car is moving. Something about the airflow around the car is causing this, hence my reference to aerodynamics & question on wind deflectors. 

[jaynana]

i know what you mean mate..

its the 'buffeting noise'. i get it too as i like to drop the window down when i can, as said opening a rear window helps.

but more importantly i've never had a car which doesn't do this.  a bit of google shows i'm not alone in that.

more importantly i don't believe it classifies a car as aerodynamically bad cos if you think about it, the trade off to reduce that is to build a wind deflecting shape (the same thing that you try to do by fixing a deflector), which in effect increases drag even when windows are open. do we want that? no, cos that means reduced fuel efficiency, reduced speed, etc..

so what do manufacturers do? they all make cars which are super aerodynamic when windows are closed but to hell with it when windows are open!

a good read

if i were u i wouldn't bother with wind deflectors - cos they look ugly plus as above.. just slightly open a rear window.