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. |
This has been brought up before. However, I don't have any info to add. Hopefully someone can confirm.
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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:
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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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. Thanks. |
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. ;):D |
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. |
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 .. :thumbup: Otherwise the sticker would have to say; YMMVBOGCAE - Your Mileage may vary based on ground conditions and elevation |
I always thought the last gen EPA ratings were pretty accurate. The new ones "legitimize" the asinine driving of today.
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Thanks for the info on EPA testing Aerohead. |
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