Believe It or Not: you get better milage with tailgate closed.

[Bosque Bill]

For those who don't leave their camper on permanently, put your tailgate back on and leave it up/closed.

Driving with the tailgate down actually decreases your gas milage, which I didn't know until I stumbled upon this episode of Mythbusters.

Here's a quote from the web article:

...when MythBusters Jamie Hyneman and Adam Savage drove identical trucks under the same conditions across the desert — one with the tailgate up and the other with it down — Jamie's tailgate-closed pickup outlasted Adam's by more than 30 miles (48 kilometers).

Closing the tailgate actually improves fuel efficiency because it creates a type of airflow called a separated bubble within the bed of the truck. As wind rushes over the moving truck, that bubble of slow-moving air deflects it over the raised tailgate. By guiding surrounding air over and across the bed of the truck, that vortex effect prevents added drag.

However, driving with the tailgate open eliminates the bubble effect, pulling the air toward the truck bed and creating more drag rather than deflecting the wind. Some gas-conscious pickup drivers still swear by leaving their tailgates open, but science sides with leaving it up.

 

[Espresso]

Makes sense, but still seems counter-intuitive. Did they swap trucks and repeat the experiment?

 

[Bosque Bill]

Makes sense, but still seems counter-intuitive. Did they swap trucks and repeat the experiment?

Unfortunately, I just caught the very end of the segment, so don't know what all they did other than what the article says.

 

[chnlisle]

Here's the article;

http://dsc.discovery.com/tv-shows/mythbusters/mythbusters-database/driving-tailgate-fuel-consumption.htm

 

[Bosque Bill]

Here's the article;

http://dsc.discovery.com/tv-shows/mythbusters/mythbusters-database/driving-tailgate-fuel-consumption.htm

Yes, I did include that link in my original post.

 

[craig333]

Mythbusters aren't the only ones who've tested that theory. Pretty sure some govt agency came to the same conclusion.

 

[Marshfly]

As did every automaker many years ago. Do you really think they'd be putting solid tailgates on trucks today if they weren't better for mileage with the CAFE ratings as high as they are?

 

[ntsqd]

What people seem to have forgotten is that trucks are supposed to be work vehicles first and foremost. Any sort of vented or absent tailgate would really not work well for hauling manure or gravel.

That said, the telling thing isn't that the tailgate is still there. It is that the OE's have put significant effort into sealing them to the bed when closed. That pool of slightly compressed air in the bed only works if it can't leak out around the tailgate.
My '67 Ranchero got better slightly mileage with the tailgate down than it did with it up. The reasons for that were no such sealing around the tailgate (nor any reasonable way for me to add such); and a that it was a forward sloped flat surface "scooping" air into the bed.