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Tags: Chevrolet Volt, Opel Insignia, Audi A4, Toyota Prius, Hybrids, Aerodymanics

Tag Links: Chevrolet Volt, Opel Insignia, Audi A4, Toyota Prius, Hybrids, Aerodymanics

Guess Which One Of These Cars is the Most Aerodynamic...
“Aerodynamic drag has a significant effect on a vehicle’s fuel consumption. This is the reason why fuel-efficient family cars like the Toyota Prius and Honda Insight look so alike (and boring) as their shape is virtually dictated by aerodynamics”. How many times have you heard this? Well, guess which one of the above cars is the most aerodynamic... Read Article
Guess Which One Of These Cars is the Most Aerodynamic...



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GreenPleaseGreenPlease - 10/10/2008 8:57:57 AM
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While I agree that many designs use aerodynamics as a cop out, the article made an enormous blunder: they forgot what coefficient of drag was designed to calculate. Cd is designed to calculate a car's effective frontal area. You can get a lower Cd, ironically, by making a car bigger but your effective frontal area remains constant.

An example of a car getting bigger but having a lower Cd is the Mercedes CLS and the S. The S class is considerably bigger but it has a lower Cd (.25 I believe) while the CLS is smaller but has a higher Cd (.31). Both cars have roughly the same frontal area which explains why they have about the same highway fuel economy rating.

Cars like the prius, insight, and volt go beyond aerodynamics. They are also trying to make the car as light as possible, which inherently means as small as possible, while maintaining certain interior dimensions. That is why the teardrop shape shows up so often. It maximizes interior room while minimizing drag and overall size.

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t_bonet_bone - 10/10/2008 9:42:48 AM
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Nice post. You beat me to the point...people love a single number, but frontal area is a king, and never published.

Also, there is a large element of drag with tires/wheels...a key reason I've been babbling on for years about minivans being a better vehicle for families than SUV's. I find the lack of hybrid and/or diesel minivans especially frustrating.


LexusKindaGuy12LexusKindaGuy12 - 10/10/2008 10:21:08 AM
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the S class cannot have a cd of .25. thats impossible. the LS460 has one of .27 and i believe its best in class


M35MTM35MT - 10/10/2008 1:39:25 PMView My AgentSpace
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Good post Greenplease, one point most dont get about the Prius' ugly appearance is the advantage of increased interior volume in a small package. It's what makes the minivan so ugly, but gives it massive cargo space.


RudermanRuderman - 10/10/2008 1:47:46 PM
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A quick search at http://www.absoluteastronomy.com/topics/Drag_coefficienyielded:
0.27 - Infiniti G35 Infiniti G35, 2002
0.27 - Mercedes-Benz W203 Mercedes-Benz W203, 2001 - 2007
and
0.26 - Lexus LS 430 Lexus LS, 2001
0.26 - Mercedes-Benz W221 S-Class Mercedes-Benz W221, 2006

So - No - not 0.25

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GreenPleaseGreenPlease - 10/10/2008 3:24:16 PM
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I should have said "I believe I'm within .01 for the Cd of the S and CLS"


cericceric - 10/10/2008 2:04:52 PM
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"Drag coefficient" is after all just a coefficient.
Front wind resistance = frontal area x drag coefficient
The frontal area of a Prius is almost like a square box to maximize interior space and reduce weight. It is very difficult to reduce coefficient when you have to work from a boxy shape.
The sedans listed (including Lexus LS) has a wider bottom and narrower top side. Not boxy. It is easier to reduce coefficient from that sort of shapes.

Please name a minivan that has sub 0.3 coefficient?
Modern CUVs (frontal area more boxy than sedans) have coefficients in the range of 0.34 to 0.38. That gives you an idea that making is below 0.3 is tough. On top of that, the length of vehicle also impacts the coefficient. Longer vehicles have lower coefficients (assume everything else being equal). As a result, you get the Prius shape (similar to the new Honda Insight)

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huu76huu76 - 10/11/2008 12:40:52 AM
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Put some underbelly plates and spoilers on the Prius, Cd number fixed.

I remember Infiniti offering that option on the G35s.

Sounds like Cd is just like HP which can be manipulated simply by making an engine spin faster or adjusting some numbers in the formula.

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