Why do Ford's new hybrids ace the EPA fuel economy tests?

When real-world fuel economy doesn't match EPA estimates, the difference may lie in the cars' design. Ford's new C-Max and Fusion hybrids fall far short of their "47 city/47 highway/47 combined mpg," according to a growing number of reports.

Consumer Reports' road tests yielded similar results. For example, we clocked a much lower, but still outstanding, 41 mpg for the Fusion and 38 mpg for the C-Max in our highway tests. That difference in mpg may be linked to the way the Ford hybrids work.

Ford's system can operate in full-electric mode at speeds up to 62 mph. That ability can greatly improve fuel economy in the EPA highway cycle, since most of the government's simulated driving test measures gasoline used while driving at lower speeds. But it won't help at all in the highway portion of the Consumer Reports fuel-economy test, which measures gas consumption at 65 mph. The gap between these results may disappoint those who regularly cruise on the highway at speeds greater than 62 mph.

How the Consumer Reports and EPA highway tests differ
In the Consumer Reports highway test, we record the average fuel usage in two directions at a steady 65 mph on a specific section of highway. In contrast, the majority of the EPA highway cycle simulates a vehicle traveling mostly at speeds below 55 mph. Although the EPA tests reach 80 mph at times, the highway tests include a fair amount of gentle acceleration and coasting. Speeds average only about 48 mph. Under these conditions, Ford's hybrid drive allows the gasoline engine to completely shut off at times, with the resultant increase in fuel economy.

When we compare Consumer Reports' test results to the government agency figures, we usually find that our numbers fall short of the EPA for city driving, but they exceed the EPA results on the highway. The Ford hybrids, however, stood out in our testing by falling far below their EPA highway estimates. (Learn more about how we test cars.)

In contrast, the similar Toyota Camry and Toyota Prius V hybrids follow the conventional pattern in our tests: Both easily exceed their EPA highway rating in our steady-pace 65 mph test. Toyota's system operates in electric mode only below 25 mph, so those electric drivetrains don't help much on the highway with either test method.

Ford should be congratulated for producing some of the most fuel-efficient vehicles on the market. However, customers who look for 47 mpg may need to readjust their expectations. When the EPA revamped its testing cycles in 2007, it made significant strides in bringing its estimates more in line with what drivers can expect to get themselves. The EPA is looking into this latest discrepancy and may again need to address new challenges in predicting fuel-economy for emerging technologies.

Related:
Tests show Ford Fusion, C-Max hybrids don't live up to 47-mpg claims
Owners report Ford's latest hybrids don't live up to 47-mpg claims
Guide to fuel economy
How to improve fuel economy with your current car

—Jake Fisher