Hybrids built by Ford show the largest discrepancy between EPA mpg figures and real-world tests, says Consumer Reports. For example, the C-Max and Fusion hybrids fall 10 and 8 mpg, respectively, below their advertised 47 mpg.
Consumer Reports compared the EPA mileage estimates of 315 vehicles with the results of its real-world fuel economy tests and found notable gaps in cars marketed as green or fuel efficient, especially hybrids and small turbo-charged four-cylinder engines.
Consumer Reports’ real-world tests found hybrids generally get some of the best overall gas mileage in their classes, led by models including the Toyota Prius and hybrid versions of the Honda Civic and Ford Fusion. However, testing also revealed the mpg figures shown on the window sticker and in advertising often overstate the actual fuel economy of the vehicle.
The Consumer Reports test, which is published in the August issue, found 55 percent of hybrids and 28 percent of cars with small turbo-charged engines fall short of EPA estimates by 10 percent or more. That compares with only 10 percent of conventional vehicles.
Most of the cars tested by Consumer Reports exceeded their EPA highway estimates but fell well short in city mpg.
The fuel economy figures displayed on a car’s window sticker are the result of fuel economy tests performed on a rolling treadmill by automakers using protocols formulated by the EPA. The government agency then spot checks about 15 percent of the models in its own lab.
Consumer Reports conducts its real-world tests on its track and on public roads. Vehicles are driven on highway and city loops multiple times by two drivers. Testers splice a precise fuel meter into each test car’s fuel line to measure how much gas is consumed.
A separate analysis released last month by Carnegie Mellon University found vehicle window stickers, fuel economy standards and even life cycle studies offer incomplete efficiency estimates for vehicles because they often fail to account for driving conditions.