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Now that even the new G30 BMW 5 Series has 0.22cD...

Discussion in 'Model 3' started by emir-t, Oct 23, 2016.

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  1. emir-t

    emir-t Member

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    BMW showed the new looks of the BMW 5 Series, coded G30. It's more or less the size of a Model S and has coefficient of drag of just 0.22. So 8% less than the Model S.

    When Elon said Model 3 would have <0.2cD people said it had to have wheel covers for the back or that it wouldn't happen. It could even have 0.18. What do you guys think? I hope we can see a better front look though even if it means 0,01 more drag. Also, please the facelift Model S and Model X LEDs for the headlights!

    Does anyone also know how much of a difference the cD makes on range? I know it only matters at highway speeds so above 60mph but by how much I wonder. I'd love to be able to cruise 80mph and have the consumption of 60mph.
     
  2. SageBrush

    SageBrush Active Member

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    The numbers follow the drag equation, so Cd changes are proportional while differences in speed are squared.

    Assuming all else is equal (car frontal area, tyres, mass,) an increase in speed from 60 to 80 would require a drop in Cd of (8/6)^2, equal to 1.77x. So if the old Cd was say 0.3, the new Cd would have to be 0.3/1.77, equal to 0.17

    Getting close ;-)
     
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  3. Jayc

    Jayc Member

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    I am very sceptical about that claim as it looks quite close to the current design which itself is a quite dated look IMHO but that is a different question. Not long ago, Mercedes made headlines claiming their CLA sported an industry best Cd of 0.22 and we all thought that that was indeed an achievement seeing as the other low drag designs at the time were all quite boring in comparison. MB maintained their claim for years until an independent organisation did measurements and discovered it was nowhere near 0.22 but by then no one was listening. I don't want to label everyone cheats without proof but I can tell you it's not an easy job reducing Cd and keeping decent proportions.
     
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  4. emir-t

    emir-t Member

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    Spot on. Just checked and the Cd of the 2012 Corolla converted EV I have is exactly 0.3. If the Model 3 has 0.17(very difficult) assuming it has the same frontal area (would be pretty close to a Corolla) I could zip past 80mph and have the same consumption level of 60mph (~270wh/mi) with the old car. Pretty cool.

    It's interesting BMW could get much lower than the Model S, which when debuted presented 0.24Cd as a big deal. 8% is a big deal at this levels.
     
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  5. McRat

    McRat Active Member

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    BMW can claim any numbers they like for Cd, or engine output. Companies exaggerate these numbers constantly.

    The real proof will be Fuel Economy or miles/kWh if EV.

    All the marketing numbers in the world never actually change a car's behavior. Exception - Stickers on cars or raspy loud exhausts, can add horsepower. They don't affect mileage though.
     
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  6. SageBrush

    SageBrush Active Member

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    Let's reverse the question since the MS is said to be 0.22 Cd. How much faster can it go than Corolla traveling at 60 mph and end up with the same drag? *

    The Corolla has 30/22, = 1.3636 higher Cd,
    So the MS can speed up sqrt(1.3636) = 1.167
    60*1.167 = 70 mph.


    *Again assuming other parameters equal.
     
  7. outie

    outie Active Member

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    It's not simply from exterior design. It's dynamic:

    This improvement in aerodynamic performance is largely thanks to the fitment of active air flaps that closes the kidney grille’s louvres to reduce drag at speed, the Air Curtains and Air Breathers that work together to cut air turbulence in the wheel wells, and airflow-channelling elements fitted across its whole underbody.
     
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  8. Red Sage

    Red Sage The Cybernetic Samurai

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    Yadda, yadda, yadda... Izzat with or without exterior rearview mirrors? Traditional automobile manufacturers seem to always mysteriously sort of 'forget' to use their mirrors when determining such numbers and stuff.
     
  9. malcolm

    malcolm Active Member

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    They should have claimed 0.19 Cd - but then everyone would have asked "why doesn't it look more like this?"

    [​IMG]
     
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  10. RobStark

    RobStark Active Member

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    Mercedes could achieve those numbers. On an ultra limited edition Eco Model available only in Europe.

    With active aero, special front and rear fascia, plus underbody contour cladding.

    Skinny LRR tires, aero wheels, etc.

    But they implied you could get the Cd on a typical CLA.
     
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  11. eisbock

    eisbock Member

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    Yes, highly suspect.

    There is nothing on this car that suggests it's anywhere close to .22. The only thing it's got going for it is the rounded "pointy" front. It's not wide and flat, but tapers from all angles to a "point". This is where Tesla is really shooting themselves in the foot. The nosecone was good, but flattening the front on the new models is raising the Cd. Fortunately, not by much because the part that first contacts the air is still relatively small in area. The teardrop is the most aerodynamic shape and a rounded Saleen-esque front fascia is the best design.

    But, even then, that's only one piece of the puzzle. There's too much going on on the front and sides to promote smooth airflow. The windshield is too upright and juts backward too suddenly. That's going to launch air upward, creating a low pressure zone on the roof and all that air comes crashing down on top as turbulence. The trunk area slopes down too suddenly. There is a reason the Model S has an elevated trunkline compared to other sedans with a gentle slope to the spoiler. You want to guide air to the back as smoothly as possible and the 5-series is going to have another low pressure zone on top of the trunk adding turbulence to the turbulence.

    Now, Tesla has another problem with the high trunk because air has to go behind the car and usually gets sucked right into the back, causing turbulence. if you can slope the rear of the car all the way to a point (again with the teardrop), you can eliminate low pressure zones and turbulence. This is why the "kammback" (seen in images above) is so great. It moves the car further toward the elusive teardrop shape for maximal aerodynamics. But this obviously looks ridiculous, so what's the next best option? Spoilers or spoiler shapes. These are great at mitigating this effect and that's why all Teslas have a "spoiler" built right into the body panels. This is extremely exaggerated on the 3 for maximum aerodynamics.

    The 5-series has none of this. Additionally, the back of the 5-series has lots of stuff jutting out... taillights, trunk, crazy "sporty" lines, tailpipe (!). It is also angled straight down and is boxy. Tesla is smooth and sloping and the bottom sticks out a bit (back is angled) to alleviate the turbulence as much as possible. It's also round when looking at a top down view. This is still the worst part of the car, but is designed as best as possible while still looking good.

    And another thing! Throw that antenna shark fin on the top and there's another aerodynamic problem. Not by much, but anytime you have a shape where air flows over or around and then suddenly there is no more shape, just empty space, that's turbulence city. You want air to hug the contours of shapes as much as possible.

    This was fun! But there is no way in hell the BWM car revealed in that article has a .22 Cd. Also, this wasn't meant to be a lesson to you, I just happened to start typing and the keyboard got the best of me.
     
  12. Garlan Garner

    Garlan Garner Well-Known Member

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    Hmmm it comes in a Diesel verrr ( a-hem) rrss ( cough cough ) iiooo ( hacking ) on.

    Sorry, it has a diesel version ( ahem ). I can't clear my nostril from all of the black smoke from the exhaust.
     
  13. EV-lutioin

    EV-lutioin Active Member

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    If MS has .22Cd and M3 has .18Cd, what is the Cd for the MX?
     
  14. Garlan Garner

    Garlan Garner Well-Known Member

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    Who's really concerned about drag coefficient in a Tesla? It doesn't affect the gas mileage.

    The only way I would be concerned about it is if it affected my 0-60 times.
     
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  15. EV-lutioin

    EV-lutioin Active Member

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    But, what about range.... isn't range one of the most important limiting factors in an EV?
     
  16. Garlan Garner

    Garlan Garner Well-Known Member

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    Anything over 125 miles of range is a beautiful thing in EV.

    Ludicrous 0-60 is beautifuller.
     
  17. Garlan Garner

    Garlan Garner Well-Known Member

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    No, Range isn't an issue with Teslas. To me...any EV that has a 200 mile or more range per charge is just fine.
     
  18. T34ME

    T34ME Member

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    Hmmmmmmmm, this sounds like the stuff of a poll! A range of much greater than 200 miles is VERY important to me.
     
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  19. EV-lutioin

    EV-lutioin Active Member

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    Agreed, I find the 250 mile range on my MX 90D to be limiting on many trips. Case in point, we are traveling to Yosemite in a few weeks and it is a bit of a puzzle range wise.
     
  20. Garlan Garner

    Garlan Garner Well-Known Member

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    Then take an ICE.

    No matter how many miles a tesla can travel on one charge....there will be someone who needs another 10 miles in their endeavors.

    250 is more than enough for me.
     
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