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Discussion Starter · #1 ·
An aerodynamic comparison of five car was described in the June 2014 issue of Car and Driver magazine. The Volt's performmance was disappointing, falling significantly behind the Toyota Prius and Tesla Model S. I couldn't find a link to this story but here is a summary.

The cars tested were:
Chevy Volt (CV)
Mercedes Benz CLA250 (MB)
Nissan Leaf (NL)
Tesla Model S (TS)
Toyota Prius (TP)

Calculated Drag Coefficient
CV 0.28
MB 0.30
NL 0.32
TS 0.24
TP 0.26

Equivalent Drag Area (CD X Frontal Area) (square feet)
CV 6.7
MB 7.0
NL 7.8
TS 6.2
TP 6.2

Aero Power @ 70/100 MPH (hp)
CV 16/45
MB 16/48
NL 18/53
TS 14/42
TP 14/42

Lift Front/Rear @ 70 MPH
CV -15/26
MB 46/44
NL -12/11
TS 23/17
TP -4/17

What's interesting about this is I actually spoke with the aerodynamist who worked the Volt. She just happened to be at the Chevy Volt test drive in San Diego. She said she they had done extensive development on the Volt in the wind tunnel and was the most aerodynamic car produced by GM. When asked if she had comparedthe Volt with the Prius. She answered yes, the Volt was a couple "points" better as tested in the GM wind tunnel. I don't believe anyone is lying, but why do you think the Volt performed so poorly in this test?
 

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Does not surprise me. Car & Driver is comparing some other cars with extremely low drag characteristics. The Volt is far above average... But it does not surprise me that a Prius has better numbers. On the other hand... The Prius is downright UGLY... compared to the Volt. (In my opinion.) And thank Chevy for the fact that the Volt does not look like a Leaf...
 

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Comparison test implies C&D did some testing. What I'm seeing here is just C&D doing a bunch of calculations using the manufacturer's published numbers. That's an important distinction...

First of all, there can be variation between wind tunnels and calculation methods. If an independent lab tested them all on the same day in the same tunnel the same way, these numbers might change a little.

Second, and possibly more important, the manufacturer can choose the exact configuration to test/present. GM has said repeatedly that the Volt is more aerodynamic /has less drag than the Prius in their testing, and I believe that's true.

In the more detailed articles and videos, it is pointed out that GM tested the 17" wheel equipped Volt against the 17" wheel equipped Prius Touring model - GM's idea of apples to apples. On PriusChat it's commonly accepted that the 17" Prius will get lower mileage than the 15" Prius from what I've read.

I'm pretty sure Toyota is quoting the lowest drag model they have - and GM is testing one with more drag. Given that most Priuses delivered are 15" wheel models, I'm not sure which approach is most fair.
 

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Discussion Starter · #4 ·
Sorry, I should have mentioned that C&D actually tested each of these cars in the same wind tunnel under the same conditions.
 

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I believe a GM engineer has stated that it was curious that no one has been able to duplicate Toyota's claimed numbers. Its time to look a different kind of cash on the hood. A Prius would have cost me $2,000 dollars more to drive the past year. Those are the numbers that count to me. Your results may differ just like these drag coefficient numbers do.
 

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but why do you think the Volt performed so poorly in this test?
Not exactly "poor" is it?

I recall back in the Volt development they were talking about areo and how they choose to use normal sized tires vs narrower tires and traded ride/handling for a little areo.
 

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I don't understand, and I'm open to an explanation, about why this type of stuff bothers anyone. I bought a Volt because I like the Volt. It only needed to be highly rated for safety.
 

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....Aero Power @ 70/100 MPH (hp)
CV 16/45
MB 16/48
NL 18/53
TS 14/42
TP 14/42

.... I don't believe anyone is lying, but why do you think the Volt performed so poorly in this test?
are you just trying to generate clicks for car and driver???

"poorly"???? I'm sorry but 16 horsepower at 70 mph is not "poorly" in my book nor anyone else who understands these things.

use of the word "poorly" in this situation is "the use of perjorative language to misinform" and is either unaware, unbalanced ,or obnoxious - take your pick.. none of the other numbers really matter, I don't drive 100 mph, I don't really care about 25 pounds of lift, CD and EDA are interesting only in academic terms. What I know is that I have a 149 HP car with 16 used to push the air aside at 70 MPH, that leaves me 133 HP to accelerate, THAT is great, and I think better than the leaf or prius, but certainly not as powerful as the model S, or CLA250......
 

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I don't understand, and I'm open to an explanation, about why this type of stuff bothers anyone. I bought a Volt because I like the Volt. It only needed to be highly rated for safety.
I agree. I drive almost 20K miles a year and I'm doing over 90% of it on electricity. Try that in A PIP. As to the Tesla, it's out of my price range, I'm not ready for a BEV, and I don't want to be left with an orphan when they finally follow Fisker into oblivion, LOL.
 

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I recall back in the Volt development they were talking about areo and how they choose to use normal sized tires vs narrower tires and traded ride/handling for a little areo.
As a former Prius driver- I'm glad the GM Engineers decided on comfort and handling!
What good is great economy if you're uncomfortable?
 

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Sometimes you need to take a step back and ask if your test results make any sense. The Volt has a higher MPGe rating than the Model S. But of course that would be impossible if the Model S had lower drag.

Testing in wind tunnels is not so easy, apparently. I'd go with the test results from Ford and GM rather than Car and Driver. (BTW I think a couple of points means 20 counts).
 

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Lets not forget that the Volt gives up over 600lb to the Pirius with most of that being battery and more steel as well as more safety. Of course Tesla gives over 100lbs to the Volt but both the Pirius and the Volt have more overall internal friction than the Tesla. These factors are bound to have effects on the overall road horsepower requires to maintain speed.
 

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Lets not forget that the Volt gives up over 600lb to the Pirius with most of that being battery and more steel as well as more safety. Of course Tesla gives over 100lbs to the Volt but both the Pirius and the Volt have more overall internal friction than the Tesla. These factors are bound to have effects on the overall road horsepower requires to maintain speed.
What exactly do you mean by "overall internal friction"? The point is that if the Model S was in fact more aerodynamic than the Volt then it would have a higher MPGe rating than the Volt. It doesn't. Hence you know it isn't more aerodynamic.

I guess you're saying that the lower internal friction of the Model S makes the test result even more silly, but I don't know what you mean by this.
 

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The point is that if the Model S was in fact more aerodynamic than the Volt then it would have a higher MPGe rating than the Volt. It doesn't. Hence you know it isn't more aerodynamic.
MPGe folds in a bunch of things besides aerodynamics. Rolling resistance, drivetrain losses, motor/inverter efficiency - even charging losses are a part of the number I believe.

Since Tesla is getting ~10% worse mileage with ~5% less aero losses (and presumably ~30% more rolling resistance, though that's a relatively small factor at the freeway speeds they are discussing,) I'm thinking they have lower efficiency elsewhere in the system. Motor inverter losses are the most likely candidate, I'd think. Note that the RAV4 EV with it's Tesla drivetrain also gets rather poor MPGe compared with the industry - substantially worse than the Model S actually (78/74, 76 MPGe combined.)
 
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An aerodynamic comparison of five car was described in the June 2014 issue of Car and Driver magazine. The Volt's performmance was disappointing, falling significantly behind the Toyota Prius and Tesla Model S. I couldn't find a link to this story but here is a summary.
~
What's interesting about this is I actually spoke with the aerodynamist who worked the Volt. She just happened to be at the Chevy Volt test drive in San Diego. She said she they had done extensive development on the Volt in the wind tunnel and was the most aerodynamic car produced by GM. When asked if she had comparedthe Volt with the Prius. She answered yes, the Volt was a couple "points" better as tested in the GM wind tunnel. I don't believe anyone is lying, but why do you think the Volt performed so poorly in this test?
A jump into the Voltec WayBack machine will answer all!


Chevy Volt’s Coefficient of Drag is 0.28, Beats Prius and Insight

"This number is for the Volt IVer which is representative of our production car. We were resistant to give out the number earlier for two reasons. One we wanted to wait until we tested our IVer. Also, we didn’t want to report it out until we saw where the competition was because we know that those numbers depend on how the tunnels are calibrated.

If I quoted 0.28 a year ago people would have said ‘aha’ the competition got 0.25. But its really all relative to what tunnel it was tested on.

The base Prius with the smaller wheels may come in lower, but we don’t offer 15 inch wheels."

Bob Boniface who is chief of Voltec Design


Link Goes To Dr. Lyle Dennis Article, GM-Volt, December 4th, 2009-

http://gm-volt.com/2009/12/04/chevy-volts-coefficient-of-drag-is-0-28-beats-prius-and-insight/



My Very Best-

Thomas J. Thias

Sundance Chevrolet Inc.

517-749-0532

Twitter.com/AmazingChevVolt
 
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