How the EPA tests fuel economy
Thursday December 28, 2006
Ever wonder how the EPA arrives at the fuel-economy estimates that appear on each car's window sticker (and in every About.com Cars test drive) -- or why the numbers tend to be so optimistic? Yep, me too. So I did a little digging to find out more about the test procedures, as well as the changes coming in late 2007 that will make those numbers more realistic. Get the full story: How the EPA tests fuel economy. -- Aaron Gold
More to read:
Image © US Environmental Protection Agency
Mr. Aaron,
I am very curious as to why you can’t report what mileage you actually get while doing the testing. Why can’t you put in the kind of driving that was done, (I’m assuming that it runs from one extreem to the other) and then report both the sticker mileage and your mileage, like Consumer Reports does? With this becoming such an important issue, I would think that many would like to see your results.
Jim – We do report our test mileage in some reviews. The problem is that we don’t drive the exact same route under the exact same conditions (weather, temperature, etc.), so it’s hardly a scientific comparison. Our testing also includes hard acceleration and a bit of agressive driving, so our observed mileage is bound to be lower than what most owners will see.
When I do talk about test MPG in my reviews, I also talk about the kind of driving I did and whether I consider my observed mileage to be good or bad. Generally I average 10 to 20% lower than the city figure, hybrids excepted. Anything that exceeds the city figure during test week is doing pretty well. – Aaron Gold
Thank you for responding Aaron.
I understand the agressivness that your testing includes. That’s what I meant by “from one extreeme to the other” comment. I live in Minneapolis, Mn. My driving is a lot like that, I think. From holding it to the floor boards to hard on the brakes. To give you an idea, I usually get around 18 to 21 mpg with my malibu 3.1 V6. I just was curious. Thanks again for responding.
Fuel economy involves a lot of variables. I’ve found that my driving style gives 10 to 20% better than EPA ratings when driving a manual transmission car and 10 to 20% worse when driving an automatic. This generally applies to all vehicles that I’ve ever driven (numerous).
My theory of the reason is that I reduce pumping losses with a manual (BMW did a study on this a number of years ago) and that driving style isn’t possible with an auto.
Fuel economy is probably the most subjective feature on a vehicle. How fast you drive, how far you drive, how well you drive, even, all play a part. What’s the weather that day? Do you let your car warm up in the winter? How often do you use the air conditioning? Unless we all drive identical, down to the last mile, no one will ever get the same fuel economy. I think there should just be one number that says you’ll get between xx and xx for this vehicle, and just leave it at that. I think a more important number is the size of the fuel tank!