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Posted: May 27, 2013

Pickup Truck Tailgate Up Or Down Aerodynamics Tested

Wind tunnel testing by GM proves which method provides better fuel economy

By TTM Staff

There's been a long debate over fuel economy performance when a pickup truck's tailgate is up or down. Most truck owners agree that when the tailgate is down, it provides better airflow over the cab and reduces drag in the bed. But a recent wind tunnel test by GMC, performend on the new 2014 Sierra, tells a different tail.

According to Diane Block, GMCs aerodynamic engineer, leaving the tailgate up is more efficient than having it in the lowered position. GMC tested all aspects of the truck's aerodynamics for improved airflow and overall fuel efficiency. According to Block, the when driving with the tailgate up, the air flowing over the cab tends to fall down and then push forward against the truck, amost propelling it from behind. When the tailgate is lowered, the air escapes and doesn't add any benefit to the vehicle at all. In general, GM found that trucks get better fuel economy with the tailgate up.

While it may seem like GMC's testing shows an open bed with a closed tailgate, there are other facts to consider. The major one that has been overlooked, is that the testing was done in a 750-foot long wind tunnel with a fan that generates winds up to 138 mph. GM did not disclose or provide any indication of the wind speeds in which the 2014 GMC Sierra was tested.

Bloch also advised against nets covering the back of the truck. "Replacing the tailgate with an aftermarket net is worse than having no tailgate at all," Bloch said in a statement. "Imagine dragging a solid object and a fishing net through water. The net is going to require more muscle."

Readers Respond

If some one wishes to be updated with most recent technologies then he must be pay a visit this web page and be up to date all the time. By fedorahosted.org on 2014 07 29
I would like to know if this information applies to any puck-up truck or only the one depicted, specially whether the length of the truck bed is somehow related to the speed at wich this "invisible bubble" develops. I have performed some tests on my Mazda B2900 with a soft cover, but haven't yet performed enough "controled" tests to conclude anything. By Larson on 2014 07 02
With the tailgate completely off the truck would that change the dynamics of the test ?, also with a longer bed or short bed make a significant change in test results having the tailgate removed completely? By geo on 2014 05 23
"Myth busters" confirm Net works. Tailgate up is better than tailgate down a an "invisible" bubble ( tonneau as it were) is created by this bubble and excess air once the box is filled at speed, is smoothed as it pass over this bubble. With tailgate up air still pulls but pulls less. Drag/dead airspace cant push nor pull the truck forward. More drag is produced when down because air drops even farther down vs cab when tailgaite is up. In the absence of this otherwise invisible tonneau (air-bubble) it produces and even greater swirl of air, hence is less FE. The Net "nets" a fuel reduction of 6%. The net breaks up the even larger swirl of air into mini eddies smoothing the air. making it more slippery than if the tailgate is up. http://www.youtube.com/watch?v=r3aqHbD-O9E By Mark J Morin on 2014 01 15
Hi! This post could not be written any better! Reading through this post reminds me of my old room mate! He always kept chatting about this. I will forward this page to him. Pretty sure he will have a good read. Thank you for sharing! By almond seed on 2013 12 17
They always test with a short box, I would like to see the same test with a long box By David Bailey on 2013 09 07
Interesting article and test. I'd like to see it done with a tonneau cover on it. By Dick DeLoach on 2013 05 28

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