Changes to Fuel Economy Tests Cause MPG Drop in Many Vehicles

The Environmental Protection Agency (EPA) has put new rules in place that should make fuel economy ratings more accurate for the consumer.

These new procedures were just implemented for 2017 model year vehicles, resulting in some changed mpg ratings. In most cases, the changes are small. For example, the 2017 Acura ILX, Toyota Camry and Kia Rio Eco all lost 1 mpg on the highway, also pushing the combined rating for the Camry down 1 mpg to sit at 24. The front-drive 2017 Mazda CX-3 also loses 1 mpg on the highway along with the 2017 Chevy Equinox AWD and Ram ProMaster City.

The changes were made to the “coastdown” procedure, which is when the “vehicle is allowed to decelerate with the transmission in neutral while its speed is periodically measured.” Using that information, the manufacturer can measure the road-load force, which is the mechanical and aerodynamic drag forces acting on the car.

A road-load force number is then provided to the EPA, which is used to simulate these conditions while testing the vehicle on a dynamometer.

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In a letter to manufacturers from February of 2015, the EPA outlined its testing procedures, which now apply to 2017 model year vehicles. Most of the procedures found in the letter are there to make sure that the vehicle used in road-load force testing is as similar as possible to the actual vehicle that customers will be driving. It specifies things such as tire life, which need to have at least 4,000 miles on them before testing, and warmup procedures for the car before it is tested.

Optional equipment that adds aerodynamic drag has to be installed on the car if it is equipped on more than 33 percent of the entire line, while equipment that reduces drag has to be present on 67 percent of the whole population to be used in testing. The EPA also expects each sub-configuration of a vehicle to be tested, as each is different and will result in a different road-load force rating.

SEE ALSO: 2015 Hyundai Sonata MPG Overstated, Brand Apologizes

In the past, Hyundai, Kia, Ford and recently Mitsubishi have all used falsified road-load force settings to obtain better fuel economy ratings than what are observed in real-world conditions. This is exactly the reason why the EPA is clarifying these rules; to make sure that the fuel economy ratings used on the monroney sticker are accurate.

To check the fuel economy of more 2017 vehicles, click here.

[Source: EPA via Green Car Reports]