You're Getting What Mileage? Now, We Believe You

Written By: MyRide.com
Reprinted under license.

New testing methods will make MPG more reliable

Introduction

Vehicle owners, industry experts and environmentalists have long complained that the tests to determine fuel economy are flawed and that the numbers that appear on window stickers are mildly and wildly inaccurate. Haven't you always been suspicious of your Uncle Frank's bragging that his Crown Victoria gets 20 miles per gallon? Especially when you know he's got a lead foot and drives around with 100 pounds of sand bags in the trunk for "traction." As auto journalists here at Autobytel, we're often left scratching our heads when our testing reveals a five to 10 mile per gallon difference between a vehicle's official mpg figures and what we actually got on the road. Ironically, our information comes from the car's trip computer.

What's the Problem?

The problem isn't that auto manufacturers are lying to us, but rather that the Environmental Protection Agency, which determines mpg ratings, was using flawed testing methods. Since the 1970s, when fuel economy estimates were introduced, the EPA has determined the figures by using two laboratory tests: one for city and one for highway driving. Both were performed at an ideal 75 degrees Fahrenheit with a top speed of 60 miles per hour, and never with accessories such as air conditioning or other equipment in operation. Those of us who have steamed along the interstate at 75 mph on a 90-degree August day with the windows down and the stereo and the air cranked will recognize the flaws inherent in this approach.

Big Changes

Now big changes have been made. Starting with all 2008 automobiles, the EPA will use new testing methods that include high-speed, fast acceleration driving, the use of air conditioning, and cold weather operation at 20 degrees Fahrenheit. Using data from real-life driving studies, the Agency will also figure road grade, wind, tire pressure, load and the effects of different fuel properties into the mix to achieve mpg figures that much more accurately reflect real-world driving conditions. "It's better info," says EPA spokesman John Millett, adding that while the new mpg figures will be much more accurate, "it's up to the consumer to decide the impact on their car-buying decisions." Ideally, we'll all choose more fuel-efficient, less polluting vehicles.

What's the Big Deal?

The EPA estimates that city mpg figures will decrease 12 percent on average, but could drop as much as 30 percent for some vehicles. Highway ratings will also drop about 8 percent on average and up to 25 percent. That's substantial. The agency expects that gasoline/electric hybrids will suffer the greatest decreases because, due to their often smaller engines, batteries and electronics, they're most sensitive to cold weather and air conditioning use. For example, explains Millett, drag from a bike rack or the power draw from air conditioning "has a substantial effect on a 1.5-liter engine, but only a nominal effect on a 4.0L." Even so, if the Toyota Prius' city mpg rating falls from 60 to 45, that still ain't bad.

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