Recently, there has been a lot of flak in the air over supposed fuel economy discrepancies. “Your Mileage May Vary” isn’t enough for people anymore, but where does the fault lie?
Consumer Reports, and other people and agencies, believe the problem to be related to the Environmental Protection Agency’s [EPA] testing methods. For example, in a recent article published by Consumer Reports [CR], “The mpg gap – Some window stickers promise too much,” CR made a couple of valid points regarding EPA fuel economy testing methods [for those cars they actually test] versus CR testing methods.
Now, many people have already been poo-pooing the EPA for their ratings, some of which were actually just estimates given them by the manufacturers, but when it comes to actual testing, EPA test methods aren’t as close to real-world driving as it could be. Then again, how easy could it be to average out the driving habits of millions of drivers in the US? Interestingly, EPA testing was not originally designed for testing fuel economy, but emissions. Vehicles running a conventional powertrain are pretty easy to test, both for emissions and fuel economy, and EPA fuel economy ratings are typically within 10% of real-world results.
Hybrid electric vehicles and the new breed of tiny turbocharged engines are another matter altogether, and the EPA really needs to update their testing methods if they’re going to get closer to real-world fuel economy. The current tests, revised in 2008, are proving to be much further behind the times. According to CR research, 55% of hybrids are more than 10% off the mark, as well as 28% of the small turbocharged engines.
Consumer Reports points out that the EPA needs to include test patterns that are designed to measure fuel economy the way that drivers really drive their vehicles. Harder acceleration, higher highway speeds, and perhaps multiple drivers, could really improve the fuel economy ratings that the EPA puts on the window sticker. Finally, the estimating by the automakers has to be done away with, as even the mathematical simulations are based on the old test standards. Add a little fudging and it’s the perfect recipe for customer complaint.
Fuel economy in its purest form boils down to, in my mind, two major factors: vehicle design and driver habit. Now, it may seem obvious that my old 1993 Jeep Wrangler got better fuel economy than my current 2005 Toyota RAV4. Engine size, transmission type, and aerodynamics are so radically different between the two of them. It might not seems to obvious though, that two people driving identical 2005 Toyota RAV4s will get drastically different fuel economy measurements.
As a Toyota Expert Technician, this is probably one of the worst questions that I ever had to answer, and when the vehicle is operating within manufacturer specifications, the only thing left is the driver. I’m not a hypermiler, but my 2005 RAV4 with 107,000mi on the clock regularly averages 26mpg combined [miles/tank] with a decent mix of highway and city driving. [This past couple week’s heat wave, on the other hand, seriously put a dent in my fuel economy, but I didn’t get a chance to measure it.]
When fuel economy comes into question, I have to ask, “When do you drive? How do you drive? Where do you drive?” and the answer always scares the heck of out me.
Image © Consumer Reports