Rear Window Ventilation / Air Flow Test

[alrashid2]

Hey guys, figured I'd do this little experiment today and post about it if anyone is curious. Never had a truck before so the rear window is a cool new feature for me! I had always read that air should ventilate out the rear window, but I smoked a cigar on the ride home last week and noticed the smoke puffing past my face and out the open driver's side front window, not out the back...

I taped a piece of red marking tape to the rear window and to my driver's side front windowsill, drove down the road at about 40 MPH, and did some little tests at varying levels of openness for both windows.

Interesting find. I found that regardless of how open or close the Front Driver's window and Rear window were, the ventilation was moving air from the outside, through the rear window into the cabin, then out the driver's front window. Exact opposite of what I always heard!

The only way I could get air to move out the rear window was by completely closing all the other windows and turning the HVAC air vents up. When I did that, the ribbon on the rear window moved outward instead of in, but just barely. When opening other windows, the ribbon moved into the cabin and strongly, getting more aggressive the more you opened the rear and front drivers windows.

Just figured I'd share! I do have a hard tonneau cover so not sure if that affects things. Thanks for reading.

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[Khamsin]

When you're driving, air flowing over the cab separates behind it and creates a turbulent area in the bed. That turbulence can actually move air forward toward the cab in a slight vacuum. With the sliding rear window open, that air has an easy path into the cab — which is why you can get dust, leaves, or even exhaust coming in through the rear window even though you're moving forward.

It's basically the airflow around the truck creating a pressure difference and recirculation in the bed.

The wonders of fluid dynamics.

 

[landiscarrier]

If I have my front and back windows partially down or all the way down wind hits me in the side of the head. As soon as I open the rear slider that no longer happens.

 

[alrashid2]

If I have my front and back windows partially down or all the way down wind hits me in the side of the head. As soon as I open the rear slider that no longer happens.

Noticed that too during my little experiment. Instead of the air tumbling around your head with the window down, the air will smoothly ventilate past your head and our your window when the rear slider is open

 

[skinnyjimmy]

When you're driving, air flowing over the cab separates behind it and creates a turbulent area in the bed. That turbulence can actually move air forward toward the cab in a slight vacuum. With the sliding rear window open, that air has an easy path into the cab — which is why you can get dust, leaves, or even exhaust coming in through the rear window even though you're moving forward.

It's basically the airflow around the truck creating a pressure difference and recirculation in the bed.

The wonders of fluid dynamics.

I'm assuming that a tonneau cover can drastically reduce the turbulent air in the bed since the bed is completely covered?

 

[rocsteady]

Noticed that too during my little experiment. Instead of the air tumbling around your head with the window down, the air will smoothly ventilate past your head and our your window when the rear slider is open

That's interesting. I have rarely had the rear slider open but I'm going to mess around with it now. Thanks fellas!

 

[PapaBear351]

I vaguely remember a Mythbusters episode about this. They found that within the bed itself (with the tailgate closed), air wasn't really moving around at all, and having a cover on the bed had very minimal effect. The bed area stayed sort of protected. Opening the tailgate had a huge impact and made the entire bed a turbulent chaotic wind tunnel.

 

[purdyd]

I vaguely remember a Mythbusters episode about this. They found that within the bed itself (with the tailgate closed), air wasn't really moving around at all, and having a cover on the bed had very minimal effect. The bed area stayed sort of protected. Opening the tailgate had a huge impact and made the entire bed a turbulent chaotic wind tunnel.

 

[PapaBear351]

Ah--that's the one! No turbulent wind tunnel after all, my initial recollection was flawed.

 

[got3fords]

Ah--that's the one! No turbulent wind tunnel after all, my initial recollection was flawed.

Some of the experiments they do are really unscientific. But they had me when they added the oats in the water. Great visual.

 

[yelnoc2]

Interesint thread.....I have never, in two years had my back slider opened and only open my front windows an inch or two in summer when I park. Hardly ever open them in cooler weather either.

 

[superj]

Truck bed sides have gotten taller because oems found out they can improve gas mileage by raising the sides and outtingnthe tiny spoiler on the top fo the tailgate.

The bed creates a high pressure zone so low pressure fast air slides right over the top of the bed. The cabin has low pressure so air tries to go there.

Air, Water, and electricity try to take the path of least resistance.

 

[Pic-N-Stick]

Interesting. I'll have to see what mine does with the camper shell.

 

[superj]

You will gets lots of turbulent air behind the camper shell as it's got more dead space.

And still a very low pressure inside the shell that will let air come in and then into the cabin, if you open both cabin, she'll, and the driver window.

My grandpa always had shells on his trucks

 

[NM Mike]

I'm assuming that a tonneau cover can drastically reduce the turbulent air in the bed since the bed is completely covered?

I’m not sure that is so. I know that leaving the tail gate down does not stop the air flow pattern as some might think. The air flowing over the cab creates negative pressure below and behind the cab, which then begins to rotate behind the cab in the opposite direction of the air flowing over the cab. This will still take place even with a toneau cover.

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