• Nov 14th 2007 at 9:24AM
  • 19

One of questions that went unanswered after the debut of the Chevy Volt earlier this year was the drag coefficient. Last night at a dinner with bloggers before the opening of the Los Angeles Auto Show, GM Vice-Chairman Bob Lutz provided a clue. While talking about the Volt he said that the production version would look different from the concept but will be recognizable as a Volt. When they put the concept into the wind tunnel it was a huge disappointment. Lutz said they might have gotten better results if they put it in backwards.

[Source: Bob Lutz]

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    • 1 Second Ago
      • 7 Years Ago
      Styling a car in the wind tunnel may be best for efficiency but how many people buy a car because it is aerodynamically efficient? Most people do not look at cars as transportation appliances. We want cars that look good, and are willing to give up some aero efficiency for a good looking car. Very few concept cars make it to production without some tweaks. Even if the Volt was super aerodynamic, they would still have to raise the roof to make it practical. as long as the car delivers on the promise of the technology and looks good, it will sell well.
      • 7 Years Ago
      This makes me want to cry. GM -- and most other car makers -- for decades have considered aerodynamics an afterthought, if they thought about it at all. (And at the same time saying they couldn't make more efficient cars!)

      Their stylists -- who are treated like rock stars in the company -- design something that panders to the current fashion. Then they put it in a wind tunnel, and the aerodynamics engineers suggest changes. Then the stylists kick and scream and raise hell and claim their "vision" would be ruined by any modifications, no matter how small.

      It's stupid.

      Now you look at how Aptera designed their car. They designed it in a wind tunnel first, then the aero guys turned it over to the stylists and said, "You can change anything as long as you don't increase the drag coefficient."

      That's how you design a car for efficiency.

      • 8 Months Ago
      Really it's a compromise between aero, weight, and battery pack size. Otherwise you would never have things like SUV hybrids, just pillbox cars. It's fine to have a less aero car as long as you meet your efficiency specs.

      They are claiming 40 miles of EV range. They can make the body as anti-aero as they want as long as they can still deliver the range.

      • 7 Years Ago
      "In fact, some American cars probably have a better drag coefficient when driven backward." - Paul MacCready discussing his AeroVironment teams continuous conflicts with GM designers on the shape of the GM Impact electric car. In the end they got it to 0.19 while keeping something of a conventional shape.

      Good thing to see that GM learned its lesson with that work! (that was sarcasm)

      • 7 Years Ago
      They designed the car without consideration of it's drag coefficient? News like this fills my with confidence that the Volt will be a technological success story.

      • 8 Months Ago
      Geez, hybrid zealot much? I was not spreading an anti hybrid message, but a why not improve efficiency of all cars message.

      At highway speed you really are not going to be putting energy into and removing it from the battery. When I hit the highway to visit relatives in another province, I have the car on cruise control for hours without interrupting it. Under these conditions a hybrid system is essentially doing nothing. I don't see a hill for hours either.

      Highway advantages are insignificant and swamped by better aerodynamics, lower rolling resistance tires, optimized gearing. Most manual transmission cars don't even have a real overdrive, turning 3300+ RPM at highway speed.

      An insight could be built to get 60MPG on the highway without batteries.

      I have no problem with hybrids and they can make sense for a lot of people, but why not build an economy car with optimized aerodynamics, optimized gearing, low rolling resistance tires, weight savings, and a smaller engine.

      What sound reason is there for only putting these simple fuel saving refinements only in hybrids? Why is no one building very efficient regular drivetrain cars.
      • 8 Months Ago
      Dear Karkus,

      The LS600 (hybrid) gets lower HWY mileage than the LS460. Both are completely embarrassed by Audi A8 diesel. Also, Car and Driver cited that their hybrid accord did worse on the HWY than the 4-cylinder Accord in their long-term test fleet.

      A typical car's drag at HWY conditions consist of 80% aerodynamic drag and 20% drivetrain and rolling resistance. The Hybrid Civic has subtle aero tweaks to help distance it from the standard version.

      The hybrids only get better mileage due to their propulsive architecture when it is in unsteady operation, stop-and-go. For steady state operation you don't need a 400lb battery pack increasing rolling resistance and a generator adding drivetrain drag.

      Look at Big Rigs. They get up to 7mpg while towing 80,000lbs. If being a hybrid on long-haul trucks saved on operating cost (of which fuel is huge) then you'd better believe they would have switched years ago.
      • 8 Months Ago
      Why is Snowdog spreading his "hybrids don't get better highway MPG" myth again ?

      Yes, the Prius and Insight are very aerodynamic, and that certainly helps highway MPG.
      look at the Camry or Civic or any other hydrid/non-hybrid comparison. The hybrid version always get significantly better highway MPG, and so obviously it's not just because of aerodynamics. The Civic hybrid is 46 MPG Highway, while the best non-hybrid civic is at 36 MPG.

      1 A hybrid allows you to use a smaller ICE (while still having the same total system power), which means it will be more efficient. Period.
      The Prius has 110 HP, for example, but it only needs a 76 hp ICE. This means it's more efficient at a constant highway speed load than a 110 hp engine car.

      2 No highway is perfectly flat (or traffic speed constant), so there will be power demand variations. Any time that happens, the hybrid electric motor can balance out the load demand on ICE, keeping the load and RPMs more constant, which improves efficieny.

      Again, the hybrid system wins. (and that doesn't even include regenerative braking on the downhills).
      • 8 Months Ago
      Pretty much all vehicles on the road could have fuel economy improved by dropping the requirement to have a 280-400hp power plant in it.

      Case in point, my Studebaker had an 85 gross hp motor, and could cruise easily at highway speeds. It had no issues driving with modern cars, other than 4 wheel drum brakes. My Cobalt may not be near as fast as it is, but I know it could do with about 50 less horse power and still be fine.

      The new Malibu does not need a 260hp six to push it, cars of similar weight and worse aerodynamics were being pushed by 100 horsepower sixes which did just fine. It's the insistence on a higher level of performance so that drivers can get from one stop light to another faster that helps keep fuel economy stagnated.
      • 8 Months Ago
      Yes this is a huge issue. We could increase fleet efficiencies dramatically with areo improvments. Hybrids don't get good econ on the highway because they are hybrids, they get it because they are aerodynamically efficient (Prius/Insight).

      Of course many people don't like the looks of the Prius/Insight. But you can still have some style with the efficiencey. I don't mind the Prius and the Honda FCX is alright and presumably efficient.
      • 8 Months Ago
      Simple solution -- put e-Flex in the Malibu as well. They would probably sell heaps.
      • 8 Months Ago
      So they're going to "sacrifice" the styling to make this brick more aero? THANK GOODNESS!

      I love the idea of a plug-in hybrid, and this has bumped GM up about 42 notches in my book (while Toyota has fallen quite a few for joining in the pissing about updating CAFE, for not dumping Panasonic in favor of a company that can make LiIon batteries etc.).... but (and I know aesthetics are very subjective) god I find the Volt ugly.

      If Aptera can get to the point of being registrable where I am that's probably the direction I'll go for my next car, just because of the purity of the engineering (THAT's what I find sexy), but who knows, maybe the redesigned Volt will be a bit more palatable.
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