Fuel efficiency tests don?t measure up
A farmer served ham every Christmas, and always chopped off the pointed end before putting the meat into the oven.
?Why?? someone finally asked.
?My dear mother always did it that way,? he replied.
?Because,? the farmer explained, ?her pan was too short for the full roast.?
His pan could hold the whole thing. But why change?
Which brings me to Jay Friedland, legislative director at the EV advocacy group Plug in America and an expert in fuel-economy testing. He told the story when I asked why ratings from the U.S. Environmental Protection Agency ? and Transport Canada, which toes the American line ? don?t match real-world results.
I?ll back up a step here.
Twice this winter I?ve criticized the official ratings.
Readers replied thusly: ?I?ve also found a little known trick. . . . To actually match or beat the ratings: Drive the speed limit.? Or: ?Sooo . . . when not in traffic (the car) performed to the EPA rating, but stuck in crappy stop-and-go traffic it didn?t!? You seriously are left scratching your head??
I called Friedland because I was, in fact, still scratching my head,
My concern isn?t the different fuel economy in city and highway driving. The tests claim to mimic both.
I also understand you consume less fuel if you stick near the speed limit, and the tests assume such cautious driving.
But the tests involve professional drivers who sit in cars on dynamometers and accelerate and brake according to precise instructions from a computer programmed to replicate ?typical? driving patterns.
The tests are known to produce overly generous fuel economy scores, and here?s where that ham comes in. Driving patterns were developed 40 years ago, when the U.S. speed limit was 55 miles (85 kilometres) per hour, and that?s still the basis for the highway driving cycle.
?I don?t see many people who average 55,? Friedland says.
Back then, too, dynamometers couldn?t handle the loads required to replicate current driving.
A few years ago, the EPA tried to compensate by adding three cycles and, in effect, boosting fuel consumption by about 30 per cent. That?s the number Americans see on car ads. Transport Canada doesn?t yet do that.
No matter, Friedland says: The arbitrary adjustment, ?doesn?t give you a lot of confidence knowing that?s how it?s calculated.?
The test cars run on ethanol-free gasoline, notes Jim Lyons, a senior partner at California-based Sierra Research Inc., a leader in fuel economy analysis. Ethanol contains less energy per litre: When, as here, it?s added, fuel consumption increases.
A second problem: The tests don?t allow comparisons because the gap between scores and actual fuel economy varies too widely among vehicles.
It?s difficult to pinpoint why this is, Lyons says, but different propulsion technologies respond differently to test conditions and real-world driving styles.
The tests don?t account for aerodynamics, crucial for fuel consumption at higher speeds, Friedland adds.
In urban driving, hybrids get their efficiency advantage from regenerative braking. The tests assume a certain number of stops, but if there are more, or fewer, in real-world driving, fuel consumption may be substantially different.
Manufacturers may select technologies that work best on the tests as long as they don?t alter performance specifically for the test, Lyons says. ?It?s a grey area.? If, for example, a car is designed for high efficiency on the dynamometer it may get much different results with a driver focused on power.
Better cycles are available; why not update the tests?
?The EPA wants to do the right thing, but it?s hobbled by its history and the influence of the auto makers,? Friedland says.
Corporate fuel-economy standards are directly linked to the tests. If more accurate tests boost fuel-consumption numbers, manufacturers would have to do more to meet government standards, or governments would have to lower the standards, Lyons says. Both create difficulties.
Still, change might come, he says. ?With all the attention being paid, it?s starting to increase political pressure. It hasn?t reached the point yet where I think you?ll see a fundamental shift.?