Pickup Truck Tailgate Up Or Down Aerodynamics Tested

Discussion in 'Chevy Truck Talk & GM News' started by Enkeiavalanche, May 28, 2013.

  1. Enkeiavalanche

    Enkeiavalanche Moderator

    [h=3]Wind tunnel testing by GM proves which method provides better fuel economy[/h]By TTM Staff
    [​IMG]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."
    [h=2]Readers Respond[/h]

    Check out the new Rear bumper.....Avalanche style...
  2. SurrealOne

    SurrealOne Former Member

  3. steved

    steved Former Member

    We figured this out in the diesel world a while ago...by watching the smoke from guys' stacks. One with the gate up simply floated across the bed and down, one with the tail gate down got swirled around in the bed. I want to remember a couple guys tried to see if it affected their race numbers, but I can't remember the outcome.

    One thing to add to this discussion is the tailgate cap. My experience is with Dodges, but the GMs are similar. If you look at a 1500, they have a cap that is almost a small spoiler, while the HDs don't have that feature. If you watch the smoke pass along a bed (gate up) without the cap, it rushes by the tailgate, then slams downward onto the bumper. The guys with the 1500-style tail gate cap installed would have the smoke exit smoothly, just past the bumper. It was noted by several Dodge owners (myself included) that, by simply adding the 1500 tailgate cap to a 2500 Cummins-powered truck, you could see a noticeable/measureable 0.5 mpg increase in your highway mileage. Point being, the CAFE standards don't apply to the HDs; and therefore don't get all the added mileage maximizing tidbits.
  4. ChromeSilver02

    ChromeSilver02 New Member

    Mythbusters also came to the same conclusion. They even used a mesh tailgate and that gave them very slim but better mph numbers over a tailgate.
  5. stchman

    stchman New Member

    The tailgate up results in better MPGs. This has been a fact for years.

    @SurrealOne, from what I've read, GM has satisfied the loan(s) terms. Can we say the same about the 700 billion that we gave the banks? Was I happy when the government loaned GM 49 billion, no. GM does appear to have made a huge turn around since 2009.
  6. SurrealOne

    SurrealOne Former Member

    I used parens in "loan(s)" because I was speaking of the 'stock', 'loan', and 'escrow' portions of the bailout which, in total, constituted the 50 billion dollar bailout which is, effectively a taxpayer-based loan/investment in GM. Only the 'loan' portion of it has been repaid, so far as I'm aware. And GM apparently paid it back with cash from the escrow portion. Given this, they're gaming the system every bit as much as the banks (don't get me going on THAT).

    This is probably worth 1.5 mins of your time...


    And this seems to support it:
    http://www.politifact.com/truth-o-m...ent-barack-obama-campaign-video-says-auto-co/


    Back on topic -- I wonder what a wind tunnel test with a tonneau cover would look like. I'd especially like to see a hard versus soft cover test in addition to comparison with no cover. I say this because the pressure zone might change based on materail type ... as opposed to complete lack of it -- and that would potentially change the shape of the air flow.
  7. ChevyFan

    ChevyFan Administrator Staff Member

    Stay on topic. :sign0018:
  8. Pikey

    Pikey Moderator Staff Member

    I don't like those rear fender flairs or wheel liners on that truck. I think that it looks cheap
  9. stchman

    stchman New Member

    I agree, I really don't like that plastic around the wheel wells either.
  10. Pikey

    Pikey Moderator Staff Member

    I would also like to see them move the smoke stream down. I want to see why there is a "mud flap" in front of the rear wheel and not behind. It has to be because of some effect on air flow around the tire.
  11. donl

    donl New Member

    That black plastic around the wheel well is hard to keep looking black. Doesn't take long and it turns gray. I was hoping Chevrolet was done with the cladding after the Avalanche.
  12. stchman

    stchman New Member

    Only the 2014 Sierra has the dumb black plastic around the wheel wells, the 2014 Silverado does not (thankfully). At least from all the pictures I have seen.

    I gather that dumb plastic around the wheel wells and cheezy ebay LEDs around the headlights makes the 2014 Sierra more "Professional Grade".
  13. 1ATony

    1ATony New Member

    I saw the Mythbusters one. I wonder if a bed cover helps to improve gas mileage at all, on the race trucks used in the NASCAR Camping World Series they sheet metal over the back of them.

    Would have been interesting if they tried that in the wind tunnel as well.
  14. steved

    steved Former Member


    As someone else mentioned, I would bet that would depend on the cover and existing truck characteristics in the tunnel...if the wind already passes over the bed without turbulence, then adding a cover might be a wasted effort; a loose toneau flapping in the wind (my dad's truck comes to mind) might actually cause drag where as a hard toneau might not have as much drag, but weigh nearly 100 pounds (added weight negates fuel savings).
  15. McClintoc

    McClintoc Super Moderator

    This is what I was going to say. Mythbusters concluded that tailgate up results in better MPGs than tailgate down.
  16. the phantom

    the phantom New Member

    The mudflap is for when your stuck, have it in reverse and have your drivers door open and looking back that you dont cake the inside of your door and face with mud:lol:Had a friend do that and thought it was funny.


    And yet I still see many people drive around with their tailgate down.:no:
  17. ChevyFan

    ChevyFan Administrator Staff Member

    Grrrrr, the OP in this thread is from TruckingTimes ... and Google Chrome flagged the entire Chevy Truck Talk forum because of the content in the ONE POST that was copied from that other website.

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