‘Your Mileage May Vary’: Truer Than Ever with Today’s Hybrid Cars

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For months, owners of Ford’s C-Max Hybrid have complained that they weren’t getting anywhere near the 47 MPH promised on the car’s window. This week, the automaker said that these customers just may have been onto something.

On Thursday, Ford announced that in order to “better match performance and improve customer satisfaction,” it was voluntarily changing the MPG label on the 2013 C-Max Hybrid. The old sticker promised 47 MPG in the city, 47 MPG on highways, and (duh) 47 MPH overall. The new label, which comes months after rounds of driver complaints and a Consumer Reports study indicated the car got just 37 MPG, gives the C-Max ratings of 45 MPG city, 40 MPH highway, for a combined 43 MPG. (That’s still 1 MPG better than the Prius V, Ford wants you to know!)

By tweaking the C-Max label, Ford is essentially admitting that the initial ratings were inflated. As a “goodwill payment” to drivers who feel misled, the automaker is sending checks for $550 to C-Max owners, while anyone who leased a 2013 C-Max gets $325.

But how could Ford have placed the 47 MPG rating on sticker windows in the first place? First off, the numbers don’t come from tests performed by the EPA, but by the automakers themselves. That’s standard practice. The EPA runs audits on about 15% of vehicles as a way of keeping automakers on their toes. But inflated MPG ratings can and do make their way onto new-car stickers, and it’s generally only after much complaining that an EPA investigation takes place and corrections are made. It’s this process that forced Kia and Hyundai to lower the MPG ratings on several vehicles last year.

(MORE: Just How Often Are Car MPG Ratings Inflated?)

Secondly, bizarrely, Ford didn’t even test the 2013 C-Max to come up with its MPG ratings. Instead, Ford used mileage tests for the Ford Fusion hybrid as a proxy for the C-Max. And this practice was entirely OK with EPA guidelines established in 1977, which allow an automaker to use the same fuel economy label data for different vehicles so long as they have the same engine and transmission and weigh the same. The problem, as the EPA explained while announcing the C-Max’s new fuel ratings, is that, “For the vast majority of vehicles this approach would have yielded an appropriate label value for the car, but these new vehicles are more sensitive to small design differences than conventional vehicles because advanced highly efficient vehicles use so little fuel.”

A quick look at the boxy C-Max hatchback and the sleeker Fusion hybrid sedan shows that they’re designed quite differently. Anyone can see that the latter appears more aerodynamic, so it’s therefore more likely to get better mileage. Indeed, the “EPA’s evaluation found that the C-Max’s aerodynamic characteristics resulted in a significant difference in fuel economy from the Fusion hybrid,” the EPA stated in a press release.

What’s more, the mileage results from automakers’ tests are often achieved during fairly ideal conditions, and are boosted with the help of gentle driving that pushes fuel economy higher. Automotive News cited an EPA engineer’s warning that temperature, the kind of fuel used, traffic and road conditions, and one’s driving habits can all mean that actual mileage falls short of the “official” EPA rating:

“Everybody wants a label that tells you exactly what you’re going to get, but obviously that’s not possible,” Jeff Alson, a senior EPA engineer, said earlier this year. “A good general rule of thumb is that real-world fuel economy is about 20 percent lower than the lab numbers.”

(MORE: Crash Into Me: Scenes from the Nation Wide Demolition Derby)

While factors like temperature and the driver’s relative lead-footed-ness can affect fuel economy with any vehicle, they have an outsized impact on mileage for hybrids. John O’Dell, an analyst for Edmunds.com who has written about why real-world MPG doesn’t match EPA sticker ratings, released a statement explaining that the C-Max’s 47 MPG rating was achieved “under controlled driving conditions.” What’s more, “Hybrids perform best in slow, stop-and-go city traffic while for many people the daily drive is spent mostly on the freeways. These are two areas where the disconnect between EPA testing and real-world driving experiences come into play.”

An article in the August issue of Consumer Reports digs into how there’s an especially large “MPG Gap” for hybrids:

Of the hybrids we’ve recently tested, 55 percent fell short of their EPA combined city/highway estimates by 10 percent or more, with hybrids built by Ford showing the largest discrepancies.

The story noted that while EPA tests for highway mileage ratings are based on vehicles averaging 48 MPH with some stop-and-go traffic, cars are driven a steady 65 MPH during CR’s tests, in imitation of a driver using cruise control on a long trip. “In that situation, a hybrid is constantly running its gas engine, so it doesn’t get the full benefit of using its electric power. Thus, it gets fewer mpg than in the EPA test,” CR stated.

(MORE: More Reason to Be Skeptical About New Car MPG Ratings)

Plenty of individual C-Max owners can attest firsthand to how their vehicles’ mileage didn’t match up with the original EPA ratings—or the new ones either, for that matter. At FuelEconomy.gov, an EPA-run site that welcomes drivers to enter their real-world mileage, the C-Max averages 39.1 MPG, with owners reporting mileage as high as 56 MPG (in Florida) and as low as 29 MPH (Maine and Utah). Automotive News’ Larry P. Vellequette wrote that he and other C-Max owners—who were previously told that their vehicle’s subpar mileage was basically the fault of the driver—now feel vindicated that Ford has changed the rating. (Vellequete, by the way, noted that his C-Max averaged 34.5 MPG in February in the Midwest, and went as high as 52 MPG during the spring, when the A/C was off.)

Because real-world mileage for hybrids can bear no resemblance to EPA ratings, and because actual mileage can vary so widely among drivers and locations, it’s been suggested that the EPA should change its MPG ratings system, perhaps just for hybrids. Perhaps surprisingly, the EPA seems open to the idea. Here’s a passage from the announcement about revised fuel economy estimates for the 2013 C-Max:

Looking forward, EPA expects to see greater use of common high efficiency systems across multiple vehicles by manufacturers in order to improve quality and reduce manufacturing costs. EPA welcomes this emerging trend and will be working with consumer advocates, environmental organizations, and auto manufacturers to propose revised fuel economy labeling regulations to ensure that consumers are consistently given the accurate fuel economy information on which they have come to rely.

(MORE: What Drivers Can Learn from the ‘World’s Most Fuel Efficient Couple’)

OK, so based on the history here, EPA fuel economy information isn’t necessarily accurate and probably shouldn’t be relied upon. But the key phrase is “revised fuel economy labeling regulations.” Perhaps they’re coming, and perhaps they’ll be more accurate and reliable than the system we have now.