Consumer Reports has come down hard on Ford’s new ’13 Fusion and C-Max hybrids, saying its test drivers failed by a wide margin to achieve the auto maker’s claimed fuel economy.

Ford has been touting the two hybrids’ combined city/highway 47 mpg (5.0 L/100 km) rating since the vehicles launched earlier this year.

The influential consumer buying guide says it averaged only 39 mpg (6.0 L/100km) city/highway in the Fusion and just 37 mpg (6.3 L/100 km) in the C-Max.

“It’s the largest discrepancy we’ve seen among current cars, but I’m not sure it’s the biggest ever,” Jake Fisher, director-auto testing for Consumer Reports, tells WardsAuto. “About 80% of (vehicles tested) are in the 2 mpg (0.8 km/L) range (of the advertised mileage).”

Ford spokesman Wes Sherwood says Ford has received positive feedback from Fusion and C-Max hybrid consumers and notes mileage results vary depending on driving style.

“Early C-Max hybrid and Fusion hybrid customers praise the vehicles and report a range of fuel economy figures, including some reports above 47 mpg,” he says. “This reinforces the fact that driving styles, driving conditions and other factors can cause mileage to vary.”

Fisher says while both models performed well and still achieved good fuel economy, “most buyers won't get anything near 47 mpg in the real world.”

Consumer Reports tests each vehicle the same way, breaking it in for 2,000 miles (3,218 km) before beginning to collect fuel-economy data.

Rather than rely on the onboard computer to calculate miles per gallon, the Consumer Reports team installs a precision fuel meter on the fuel line.

Vehicles are then driven along a city-cycle route that consists of regimented speeds, multiple stops and predetermined idle time. For freeway testing, cars are driven on a specific section of highway at 65 mph (104 km/h).

Both tests are run by multiple drivers on each vehicle and conducted only under certain weather conditions. Results are adjusted to take into account ambient temperatures.

Fisher says the publication hasn’t received many complaints from owners of the Ford vehicles about fuel economy as both models are new to the market.

However, he says consumers posting to the U.S. government website are reporting numbers closer to those achieved by Consumer Reports than those provided by Ford.

“It’s hard to say the reason for this discrepancy,” Fisher says. “If you look at our numbers they’re much closer to what people are getting in the real world.”

The new ’13 Ford Fusion hybrid and C-Max hybrid recorded sales of 3,688 and 7,596, units, respectively, through November, according to WardsAuto data.

Fisher says that before the EPA modified its tests to better reflect real-world driving there were far more discrepancies between the Consumer Reports tests and the numbers provided by auto makers, noting early generation Toyota Prius models failed to achieve advertised fuel economy.

During less-scientific testing of the Ford Fusion hybrid by the WardsAuto staff for the annual 10 Best Engines competition, editors saw fuel-economy readouts range from a low of 38.9 mpg (6.0 L/100 km) to a high of 44.3 mpg (5.3 L/100 km) in a variety of daily commutes.

Fisher says the onboard computer results typically are close to those from Consumer Reports’ precision fuel meter.

“For the most part, the computers are close,” he says. “When they first came on the scene, we did sync many of them and see how they compared to our measurements, and we found some were a bit off.”

Despite the disparate results, Fisher says both models provide excellent fuel economy, noting the Fusion hybrid mileage was better than any midsize sedan the publication has ever tested.

“The problem isn’t that they don’t save fuel, the problem is people who purchase (the Fusion and C-Max) and expect 47 mpg will be disappointed,” he says. “(Auto makers) say results may vary, but it’s surprising to see they varied so much.”

Fisher declines to say whether the situation with Ford is similar to that of Korean auto makers Hyundai and Kia, which currently are reimbursing consumers millions of dollars for inaccurate fuel-economy claims.

“I’m not sure what accounts for this,” he says. “I know the EPA cycle is very regimented that they have to follow, but in this case it doesn’t match.”