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CNET On Cars: How the EPA does (and doesn't do) MPG tests
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CNET On Cars: How the EPA does (and doesn't do) MPG tests

4:07 /

A lot of people are skeptical of EPA mileage ratings these days. Here's a quick primer on what's behind them.

I will never get over that. Do you recall when it was impossible to put $75 in your tank? Today, it's commonplace. And the worst part is, of that 75 bucks, maybe 10 to 20 get burned on actually moving your car. The rest of it goes out as heat and exhaust, the innate inefficiency of combustion engines. That's why EPA MPG numbers, as imperfect as they are, are an obsession with motorists today. And that's why there, our Car Tech 101. Now, the dirty little secret about the numbers you see here on the window sticker that tell you the MPG, those are not done by the EPA, not in most cases. Only about 15 percent of cars are, actually, gathered by the government and tested by the Environmental Protection Agency. The other 85 percent, they were tested by the car maker themselves on an honor system. The EPA will pull in the other 15 percent on a random test basis to keep everybody honest or when there's been a lot of complaints by consumers like recently on Hyundai and Kia cars and we've also heard quite a bit about Ford Fusion and C-Max Hybrids. When they hear about a big discrepancy, they'll now call one in. And when they do that, they don't take cars out on the road and drive them. They put them on a dynamometer and hook up to a computer which does the driving on a treadmill basic and they use one of several clearly specified cycles. There's the LA-4 or City Test that stimulates a 7-1/2 mile trip that's real choppy like stop and go traffic. It takes almost 23 minutes to complete, averaging 20 miles an hour and there's a number of times when the vehicle idles. It's done with both a cold start and a hot start. And the MPG results are around a down 10 percent. There's also a cold version of the City Test which is the exact same test, but it's done in an ambient temperature in the test room of 20 degrees Fahrenheit. Then, there's the Highway Fuel Economy Test that's 10 miles in duration, averaging 48 miles an hour, no stops, and takes about 13 minutes. The car is only started once at the beginning and the results are reduced 22 percent, to be safe. Now, you may have heard about the new way, the EPA's testing mileage. Two new tests were added in 2008. There's US06, what I call the Jack Rabbit Test. It's high speed, quick acceleration, 10 minutes long, covers 8 miles, averaging 48 like the Highway Test, but hits a top speed of 80 miles an hour. It has a number of hard starts at a rate of 8-1/2 miles per hour per second. That's similar to 0 to 60 in 7 seconds. By the way, the air conditioning is not on for this or most other tests, which brings us to SC03, another one of the new tests, but this one's done with the AC turned on like you often have it. It's done in an ambient temperature of 95 degrees. It's about 10 minutes long and very city-like, 3.6 miles averaging 22 miles an hour, not freeway oriented. There are 5 times when the vehicle stops and 20 percent of the time when it's idling. One more interesting car-about, the EPA does not change its MPG rating based on electrical load of the vehicle, and this can be important. Think about all those outlets you've got where you're plugging in things to charge or, are your headlights on? Are they on high beams? Are they high intensity headlights? Or have you plugged in laptops and other things into those 110 outlets you'll find on SUVs? For every 200 watts of additional electric draw, you take roughly 1 MPG off your car's fuel economy. What's being discussed now by the EPA are new or amended cycles that better test the electrified vehicles especially plug-in hybrids and range extenders and also, doing so under very different ambient temperature conditions because there's a lot of concern that electric and highly electrified vehicles have much different performance in very cold weather. Oh, by the way, check out My MPG at the government's fueleconomy.gov website. It lets you look at real drivers' submitted MPG for all kinds of cars. So, you can take their word instead of the actual tests. You can also add your data. They've also got a mobile web page that makes it easy to add your gasoline information each time you're sitting there filling up.

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