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Impressive aero attention to detail

Discussion in 'Gen 4 Prius Main Forum' started by DieselHybrid, Mar 2, 2016.

  1. Tideland2005

    Tideland2005 Member

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    Well, that jibes.... the Volt is much heavier, and should coast downhill faster.

    Thanks for the replies, Folks.
     
  2. Chuck.

    Chuck. Former Honda Enzyte Driver

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    On the mentions of drafting, just don't do it.

    Besides, if your Cd is 0.24, it's not going to help as much

    Series of Articles About Hypermiling | PriusChat

    Got a 2007 Prius in January and one of the potential projects is covering the underside with coroplast like Aerocivic - Honda Civic modifications for maximum gas mileage - aerocivic.com.

    Since it's an election year, there are plenty of campaign signs to get - they are made of coroplast.

    got a question.

    A few people have put boattails to the end of their cars to improve the aero, but it's not practical on a Prius as it would be too long.

    Thought I saw something on the Chevy Volt to have side spoilers or something around the taillights, to control the Kamm back drag better...wondering if there is such a thing and if so how it works?
     
    #22 Chuck., Mar 6, 2016
    Last edited by a moderator: Mar 6, 2016
  3. Vman455

    Vman455 Senior Member

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    I think you're referring to the sharp cutoff on the rear, referred to as "aero-corners" by some manufacturers. The purpose is to delay wake formation by inducing separation of the flow off the back, creating a short "phantom tail." The 3rd and 4th gen Prius already have this feature, more pronounced on the 3rd gen bumper cover, and less visible on the 4th gen because it also forms the edge of the taillights for most of the car's height.

    Also, the Prius isn't too long to put a tail on, depending on one's situation....

    [​IMG]
     
    Chuck. likes this.
  4. DieselHybrid

    DieselHybrid Junior Member

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    Just a note from Car & Driver's video: The Gen 3 achieved a Cd = 0.26, even though Toyota claimed Cd = 0.25
    (Mercedes numbers fell far, far short of their marketing claim. This should be professionally embarrassing for all involved.)

    So, does the Gen 4 really achieve Cd = 0.24? Perhaps when lowered & with reduced wheel gaps- as depicted in Toyota's press release pictured in OP above.

    I guess we'll have to wait for independent tests to verify Toyota's marketing claims.
     
  5. Vman455

    Vman455 Senior Member

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    One detail almost every car journal left out when reviewing the CLA is that the American model, the CLA 250, has Mercedes--claimed Cd .28 (only the CLA 180 BlueEfficiency, available only in Europe, claimed Cd .22). See here and here.
     
  6. DieselHybrid

    DieselHybrid Junior Member

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    True, but Car & Driver achieved a dismal Cd = 0.30 for the MB in question... ouch!
     
  7. Vman455

    Vman455 Senior Member

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    That's only 20 counts higher than what they claimed. Meanwhile the Leaf, for which Nissan also claims Cd .28, returned Cd .32 in the same test.
     
  8. DieselHybrid

    DieselHybrid Junior Member

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    Nissan- yes, also professionally embarrassing, but even "just" 20 points from MB, one of the world's premier automobile marques?

    This just goes to show the value of independent tests.

    Kudos to Tesla & Toyota.
     
  9. Vman455

    Vman455 Senior Member

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    Don't forget Honda; in this tunnel, the Insight returned Cd .30 (claimed .25).

    That said, there may be things going on here that impacted the results. Every tunnel behaves differently, as you know, and the A2 that Car & Driver used is very small-section and has no moving ground, perhaps skewing the results, while Mercedes' tunnel looks like this:
    [​IMG]
    While independent tests are a good thing, the organizations conducting them often don't have access to the same kind of resources (and resulting accuracy) as the OEMs, and I think the better use of this C&D test is as a comparison of relative Cd between cars rather than absolute (the Prius' Cd here, for instance, is 4% higher than Toyota claims, while the Mercedes' is 7% higher; put another way, this tunnel showed a 15% difference in the two cars' drag coefficient, where the manufacturers' numbers indicate one of 12%. The resulting numbers would probably be different again if we put both cars in Mercedes' tunnel and then both in Toyota's).

    I wonder if C&D will continue doing tests like this (I hope they do), and when we'll see the 4th gen tested.
     
  10. DieselHybrid

    DieselHybrid Junior Member

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    Precisely, every wind tunnel is different; numerous variables mean that no two tunnel results will match- exactly. However, with facilities like the one pictured above, one would expect a little more than Cd = 0.30 from the likes of Mercedes.

    The difference between 0.28 to 0.30 may only be 20 points, but it's in the wrong direction; the direction of mediocrity. Heck, my wife's minivan has a claimed Cd that matches the "benchmark" CLA. Now the difference between 0.28 & 0.26 is significant- as one asymptomatically approaches the area of diminishing returns. To paraphrase Dr. Woll (current head aerodynamicist at Mercedes) "Cd = 0.20 may be the sound barrier for production automobiles."

    But even the experts with the best windtunnels can get it wrong. Back in '99 Mercedes' top engineers produced this aero catastrophe at LeMans:


    Who can forget what happened when the CLR-GT1 moved out of the slipstream of the Toyota entry?

    Note, this occurred not once but THRICE resulting in Mercedes completely retiring from LeMans that year in embarrassment. So it won't seem like I'm picking on Mercedes, Porsche had one of their cars at Road Atlanta do the exact same back flip maneuver at speed. Thankfully- in all events, no one was seriously injured.

    So yes, even the experts can get it terribly wrong.
    Again, kudos to Toyota's engineers.
     
    #30 DieselHybrid, Mar 7, 2016
    Last edited: Mar 7, 2016
  11. bwilson4web

    bwilson4web BMW i3 and Model 3

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    A single, least significant digit is in the noise range. If it had been off by more than one digit, there would be a problem. One digit out of 25 is 4% with some tolerance above and below.

    Bob Wilson
     
  12. Topp Cat

    Topp Cat Member

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    I own all 3 plus driven them over 10,000 miles those are my real life experiences!