Rear Window Ventilation / Air Flow Test

[BigOleOgre]

What does one of these do then i wonder?

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[NM Mike]

Would be interesting to see what it looks like in a wind tunnel with one of those installed.

 

[bigb]

I swear when I put a cab height topper on my diesel Super Duty my MPH went up.

 

[bigb]

I have a topper and when weather permits that rear window is the best thing since sliced bread. I can even leave it open when I park since nobody can get to it.

 

[Tom W8JI]

This is all about the pressure ratio between the inside of the cab compared to the pressure just outside at a window or vent opening. With side windows shut this would be the pressure ratio between the cowl (which ducts into the truck) and the rear window opening.

Everything Ford did to make trucks more aerodynamic up front decreases cowl pressure. They just can't do much out back, but everything that is done in the rear to lower drag increases the pressure behind the cab.

The only annoying thing I notice with modern better aerodynamic vehicles is wind buffeting when side windows are down and any rear window or vent is closed. I either have to shut the side windows or open the back window to make the low pitch airpulsing stop.

I don't care which way the air is flowing as long as it isn't screwing with head with that vibrating.

 

[got3fords]

What does one of these do then i wonder?

Those are there just to look stupid.

 

[got3fords]

I have a topper and when weather permits that rear window is the best thing since sliced bread. I can even leave it open when I park since nobody can get to it.

My dog likes to poke her nose out the rear window.

 

[Khamsin]

What does one of these do then i wonder?

Primarily, it separates you from your money.

As far as what it actually does to the truck, the aerodynamic benefits are somewhere between “questionable” and “written by the Amazon drop shipper.”

A cab spoiler like that is generally going to:

• Add more drag
• Disturb the airflow coming off the cab (dare I say, spoil)
• Make your truck look approximately 17% faster while sitting in the driveway

At best, it changes the appearance. At worst, it adds a little drag and potentially costs you some sustained highway MPG. You're certainly not going to bolt one on and discover you've unlocked the secrets of fuel economy. That's how we ended up with Volant throttle body spacers collecting dust in the back of Auto Zone's across the Midwest, waiting for the next clapped out '99 5.3 Vortec to get thrown on.

Granted, there are OE designed aerodynamic devices that actually serve a purpose. Our trucks, for example, have that elongated cap on the tailgate for legitimate airflow management. I'm not sure exactly what its doing; maybe adding some down force, cleaning up some of that turbulent air, or maybe keeping the parts counter guy happy when it cracks and you find out an OE piece of plastic runs about $250.

That said- far be it from me to judge how anyone chooses to bedazzle their ride. It's your truck and your money. If you like it, go for it. I just wouldn't expect the little cab spoiler to turn your pickup into a Prius with a mullet.

 

[bigb]

My dog likes to poke her nose out the rear window.

You know why don't you?

 

[stemplar]

What does one of these do then i wonder?

It improves fuel economy and performance by making the driver's wallet lighter.

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