Wind Buffering / Buffeting via Windows or Sunroof

[REXman]

BMW has the same thing. when the sunroof goes back, it has a little spoiler with some grooves in it that probably sticks out only an inch.. No buffeting. I'm sure it's the crafty design of the spoiler and maybe the cars design. I'd imagine the 3 series coupes are pretty streamline.. More so than a hatch?

[Corey_R]

Hatches natrally have a low pressure zone behind them. That's why the entire back of the car gets plastered with water and dirt as soon as they roads are wet. If it isn't raining, but the roads are wet, your entire car can be perfectly clean... except the hatch! I'm not a fluid dynamics or air tunnel engineer though, so no idea if that is causing more pressure of the wind against the car surface.

[pologti18t]

Hatches natrally have a low pressure zone behind them. That's why the entire back of the car gets plastered with water and dirt as soon as they roads are wet. If it isn't raining, but the roads are wet, your entire car can be perfectly clean... except the hatch! I'm not a fluid dynamics or air tunnel engineer though, so no idea if that is causing more pressure of the wind against the car surface.

I thought that was a Golf VI design flaw only. Surely you should write to VWA about it

[G-rig]

BMW has the same thing. when the sunroof goes back, it has a little spoiler with some grooves in it that probably sticks out only an inch.. No buffeting. I'm sure it's the crafty design of the spoiler and maybe the cars design. I'd imagine the 3 series coupes are pretty streamline.. More so than a hatch?

Sounds like BMW got it right - they are more expensive cars than a Golf so you'd expect there to be no buffeting. (The sunroof on an R wouldn't be any different to the base model Golfs).

The buffeting noise is also bad on the MK5/MK6 with the windows down, but wind noise is very quite when they are up so you can't have everything.

[AdamD]

BMW has the same thing. when the sunroof goes back, it has a little spoiler with some grooves in it that probably sticks out only an inch.. No buffeting. I'm sure it's the crafty design of the spoiler and maybe the cars design. I'd imagine the 3 series coupes are pretty streamline.. More so than a hatch?

The same principle is applied with convertibles. The Eos has a windguard that runs the width of the windscreen, that you manually deploy (pop up) when you put the roof down. If you don't pop it up, you (the driver) may not hear much difference, but any rear-seat passengers sure will!

Aerodynamics are amazingly complicated. The fact that a little spoiler can make so much difference illustrates that well.

[Corey_R]

Aerodynamics are amazingly complicated.

Ain't that the truth!

Anyone that has been watching the NASCAR in the past few years will know just how complicated the topic is. They've had a "little issue" with their "new car" getting airborne when they get turned backwards at the 190mph+ tracks. The cars have been specifically designed with aerodynamics to prevent this from happening. They've even got "roof flaps" and other devices which get deployed/activate by negative pressure to stop this from happening. And yet it's happened with rather spectacular results on 3 occasions (at least 2 of them making the non-sports section of the 6pm news on the 3 main FTV comercial stations in Australia). The cars have been designed in the wind tunnels. They've had Ford, GM, Dodge/Chysler and Toyota all take them to their wind tunnels to figure it out. When they've all drawn blanks they've engaged various Science Uni's in America and UK. They've even had assistance from NASA, the US Airforce, and a few F1/LMPS designers, since they had the issue a few years back at Le Mans etc.... and the problem has still not been able to be reproduced in the labs, wind tunnels, fluid tubs, or computer simulators. Yet it happens!

But then, this is why each year there are new F1 cars, and new road cars every few years - because all these uber-scientists keep learning new things and applying new knowledge to their products!

[Frankenstrat]

I think the problem is that with wind tunnel testing, the vehicle is stationary. In a road race the car is jiggling and twitching about all over the place. All it would take is for the forward-facing part of the vehicle to rise sufficiently for the air to prefer to pass under the car rather than over it (fluids like to take the path of least resistance) and... up she goes. The underside of the car presents itself as a spoiler pivoting around the rearmost wheels. If the car has spun and is hurtling along backwards, the lighter end of the car will be facing in the direction of travel so there is less mass at the end you need it to resist pivoting. The key is to suddenly induce low pressure under the car to keep the wheels firmly in contact with the track. How you go about that is way beyond my level of expertise.

[G-rig]

Or just don't get a sun roof and save yourself money and annoyances, they are for posers anyway to a degree.

[Corey_R]

Or just don't get a sun roof and save yourself money and annoyances, they are for posers anyway to a degree.

Yeah... I just got one so those hot 10'8" women I drive by each day can see my awesome head of hair

[dave_r]

LOL I knew there was a reason I ticked the box! You know what's for posers? That blue colour....damn those people!