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Old 07-12-2008, 01:34 PM   #1 (permalink)
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EPA Ignores Aerodynamics?

I've been looking around on the EPA and fueleconomy.gov websites the past day or so and as far as I can tell, the EPA tests completely disregard the fact that different vechicles have different aerodynamic profiles (different frontal area and different Cd).
Someone please correct me if I'm wrong, but they just run their lab test with the exhaust analysis with the vehicle on the dyno at a higher speed for highway, then subtract a flat percentage from all vehicles' fuel economy to represent aero drag. I think 22% is the number I saw, but I can't locate a link anymore.
Thoughts?
Mine is that if this is true, where's the motivation for automakers to make their cars more efficient with regard to aerodynamics / the highway? Most people purchase based on the sticker rather than looking at aero themselves.

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Old 07-12-2008, 01:39 PM   #2 (permalink)
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This has been brought up before. However, I don't have any info to add. Hopefully someone can confirm.
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Old 07-12-2008, 01:46 PM   #3 (permalink)
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Found an article with the EPA blanket percentiles they used to simulate aero effects:

EPA Mileage

Yeah... no wonder the numbers are bunk.

Quote:
According to the official EPA website, their new “in use” stats will “not affect the CAFE calculation for purposes of determining manufacturers’ compliance with the CAFE standard.” In other words, the new CAFE averages will continue to be based on the old EPA tests. Well how about that?
***
EDIT:
Here is another set of articles on EPA numbers and how.... "real" they are, or aren't.

I couldn't find the EPA test results they conduct or receive on cars which goes into their calculations. Hopefully someone can find and post a link to them.
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Last edited by azraelswrd; 07-12-2008 at 02:04 PM..
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Old 07-12-2008, 02:57 PM   #4 (permalink)
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Epa

Quote:
Originally Posted by gascort View Post
I've been looking around on the EPA and fueleconomy.gov websites the past day or so and as far as I can tell, the EPA tests completely disregard the fact that different vechicles have different aerodynamic profiles (different frontal area and different Cd).
Someone please correct me if I'm wrong, but they just run their lab test with the exhaust analysis with the vehicle on the dyno at a higher speed for highway, then subtract a flat percentage from all vehicles' fuel economy to represent aero drag. I think 22% is the number I saw, but I can't locate a link anymore.
Thoughts?
Mine is that if this is true, where's the motivation for automakers to make their cars more efficient with regard to aerodynamics / the highway? Most people purchase based on the sticker rather than looking at aero themselves.
I called the EPA a couple years ago.I talked with Dave Good,EPA Mobile Sources,Ann Arbor,Michigan,where they do all the new car certification testing.Dave told me that the carmakers provide CdA and R-R data for each make to the EPA.This data is "plugged-in" to the resistive loading on the twin-roller dynos used in testing each inertia weight class,so the dyno can simulate the dynamic loading of the vehicle as it drives the cycle map.The EPA is "aware" of aero-related stuff,however they don't set policy,they only enforce what's on the books.Those laws are the play thing of auto makers,politicians,lobbyists,The UAW,The U.S.Chamber of Commerce,good ol' boys,etc.,far beyond any authority of EPA.
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Old 07-12-2008, 03:44 PM   #5 (permalink)
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Some of us at the Progressive Automotive X Prize Forum have been trying to figure out how the dynamometer testing includes aerodynamic effects. One person said the EPA does road testing, but did not elaborate on it.

I am going to paste the aerohead response there and see if anyone can add to it.

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Old 07-12-2008, 03:59 PM   #6 (permalink)
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I've posted before wondering how the Saturn Vue hybrid and the Aura hybrid get the same results. I've been spending a lot of time at the EPA site researching my next vehicle purchase. There is a feature where you can enter your mileage results for that vehicle and the average results are displayed below the official estimates. In general, cars are reporting better than estimated mileage and trucks and SUVs report on the number or worse.

Whodathunkit?

I think we should all log in our mileage on the site and really skew the results.
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Old 07-12-2008, 05:35 PM   #7 (permalink)
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Hi All,

From Aerohead, it sounds like the EPA does include aerodynamic effects. I still think they do not include the impact of hills however. For Hybrid cars this has a negative impact on the numbers they give. A Hybrid goes up the hill on engine and electric, and down the hill it charges the battery back. So, it uses 1/2 the gas going up a non-hybrid car would and almost no gas to recharge the battery. I doubt highly that the EPA sets the dyno to drive the wheels of the vehicle they are testing. Until they do, they will not be getting hybrid car fuel economy right.
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Old 07-12-2008, 06:23 PM   #8 (permalink)
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That's why its an estimate, they can't get it right for all road conditions. For example here where I live the tallest hill is a hwy overpass ....

So rejoice in the fact that the numbers will always be off and the fact that we will always be able to show positve improvements on our fuel logs ..

Otherwise the sticker would have to say;

YMMVBOGCAE - Your Mileage may vary based on ground conditions and elevation
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Old 07-12-2008, 06:26 PM   #9 (permalink)
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I always thought the last gen EPA ratings were pretty accurate. The new ones "legitimize" the asinine driving of today.
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Old 07-12-2008, 11:02 PM   #10 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
I always thought the last gen EPA ratings were pretty accurate. The new ones "legitimize" the asinine driving of today.
Ditto.


Thanks for the info on EPA testing Aerohead.

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