The C-Max MPG Fix: Getting it Right is Good for Consumers and Automakers Alike

August 27, 2013
Don Anair
Research and Deputy Director, Clean Transportation

The recent announcement from Ford that they will be changing the MPG rating of their Ford C-Max hybrid isn’t just a reminder of how much consumers care about fuel economy, but how important it is to get the ratings right. Accurate ratings can be a challenge as vehicles get more efficient since small variations in fuel consumption are amplified in the vehicles’ MPG ratings. The experience with the C-Max is moving the EPA to reexamine some aspects of their MPG labeling certification requirements to make sure they keep pace with advances in fuel economy.  This is good news for both automakers—who tout vehicle ratings as key selling points—and consumers, who depend on MPG ratings when comparing their vehicle choices.

Small changes in fuel consumption are amplified in higher MPG vehicles

Getting the fuel economy ratings to closely represent real world driving has always been a challenge.  People have different driving habits (example: jack rabbit starts versus steady acceleration), use their cars differently (example: highway driving versus stop-and-go traffic or carrying heavy cargo), and operate in different environments (example: Minnesota winters versus Florida summers).  The EPA has made changes to how they factor in these different aspects of vehicle performance and use over the years to arrive at an average MPG estimate that reflects “typical” driving.  But as they say, your mileage may vary.


Ford recently lowered the MPG rating on the 2013 C-Max from a combined city/hwy rating of 47 mpg to 43 mpg. Photo: Flickr user mariordo59.

As cars become more efficient and use less fuel, small variations in fuel consumption are amplified in the MPG ratings of the most efficient vehicles.

Consider two vehicles, one that achieves a 20 mpg rating (consumes 5 gallons for every 100 miles driven) and one with a 50 mpg rating (consumes 2 gallons for every 100 miles driven).   What happens to the actual miles per gallon of these vehicles if the fuel consumption of these vehicles varies by plus or minus ½ gallon per 100 miles?

The 20 MPG rated vehicle would achieve 18 to 22 miles per gallon on the road – a range of only 4 mpg. The 50 mpg rated vehicle however would achieve 40 to 67 miles per gallon on the road—a whopping 27 mpg range.  That big difference in MPG is one that is pretty hard to ignore.

This example exaggerates the issue, but illustrates one reason why higher MPG vehicles are getting a lot of scrutiny by consumers.   In the case of the C-Max, the rating was reduced 4 mpg, from 47 mpg to 43 mpg, the difference of 0.2 gallons per 100 miles.  Apply that difference in fuel consumption to a 20 MPG vehicle and the rating would have dropped by only 1 mpg.

Getting MPG right: What’s at stake?

Automakers use vehicle MPG ratings as a key selling point to distinguish themselves from the competition and because consumers value fuel economy in their purchasing decisions.  When ratings don’t match performance,  it’s not just bad for consumers who aren’t achieving the fuel savings they expect, but it’s bad for business.  The  voluntary MPG rating downgrade of the C-Max also led Ford to offer owners a rebate for fuel savings they were promised but didn’t achieve.  Hyundai and Kia offered a similar financial reimbursement to its customers when fuel economy ratings had to be corrected and Honda faced a class action lawsuit and was taken to small claims court over the fuel economy ratings of an earlier model of the Civic hybrid. The underlying circumstances of each of these examples vary widely, but they highlight the importance of getting MPG right.

In the case of the C-Max, Ford utilized a flexibility built into the compliance options for EPA labeling requirements to arrive at the MPG rating. With an increasing number of high efficiency vehicles showing up in automaker show rooms, that flexibility may no longer be appropriate and the EPA is planning to revise the requirements.  The process for developing MPG ratings needs to keep pace with technology development. Both consumers and auto manufacturers stand to benefit.