The Truth About Fuel Economy Ratings
by Ann Job - MSN Autos
If your new car's actual fuel mileage does not match the fuel economy numbers on the window sticker, it's not necessarily your car's fault.
Chances are you're watching the needle in the fuel gauge of your car a little more closely these days. And you're frustrated at the fuel economy you're seeing.
Join the club.
The fuel economy estimates for new cars, provided in large black type on window stickers, can overstate fuel mileage by as much as 34 percent, according to the Bluewater Network. The network is a California-based environmental group that petitioned the U.S. government more than two years ago to change the way fuel mileage is calculated.
These estimates, mandated by the federal government starting in the 1970s, were never based on real-world driving. Instead, they're derived, sort of backhandedly, from emissions test procedures.
And the process of developing the estimates has been updated only once, in 1985.
Why the Focus Now?
While some people considered gasoline to be affordable, many American drivers didn't notice - or care to make a fuss about - the inaccuracy of the fuel economy numbers.
But after several years of gasoline and diesel price jolts, as well as an increasing awareness of the costs involved in getting oil from the Middle East, Americans are more interested than ever in the fuel economy they're getting. Or, as the case may be, the fuel economy that their vehicles are not getting.
It's also easier today for a consumer to check a vehicle's fuel economy because many vehicles have electronics that automatically calculate fuel economy as they drive.
This is especially true for gasoline-electric hybrid vehicles, where real-world fuel economy results are computed and prominently displayed on an ongoing basis.
It has become such an issue, in fact, that some frustrated hybrid owners who aren't getting the fuel economy numbers posted on their window stickers have asked dealerships to "fix" their vehicles. They've also complained to automakers.
Following Government Requirements
Automakers may not be the ones to blame.
The federal government decided not to overburden carmakers with multiple, costly tests from the start.
In the 1970s, the government already required emissions testing by automakers for each new model. So measurements for fuel economy were piggybacked on the emissions testing, where companies could utilize the same test equipment.
Current Testing Details
The emissions testing is based on a driving regimen conducted in labs. Because vehicles are stationary while being tested, they don't experience any real-world aerodynamic drag as they do on regular roads. During testing, the vehicles are on a dynamometer, where tires spin on rollers as a driver accelerates. It's sort of an automotive treadmill.
In testing, only one person - the driver - is inside the vehicle. There's no extra weight as there is when the car, minivan or SUV is carrying more people or cargo.
The test driver must accelerate, brake and idle the car according to a prescribed routine where the average city speed is about 20 miles an hour. Indeed, the city driving test cycle simulates an 11-mile, stop-and-go trip that takes 31 minutes and has 23 stops, the EPA says. About 18 percent of the time is spent idling, as if the car is at stoplights and in rush-hour traffic.
The testing is conducted in controlled conditions, with ambient temperature between 68 degrees Fahrenheit and 86 degrees Fahrenheit. There's no simulation of wintry weather or hot desert climes.
The highway portion - which the EPA also calls "non-city" because it incorporates travel on rural roads - is a 10-mile trip that averages 48 mph and has no stops, according to the EPA. The maximum speed is 60 mph, far below the 70- to 80-mph speed limits that drivers today encounter on interstates.
The impacts of fuel-using accessories such as air conditioning and heating are not measured, because this equipment is not turned on during the test. Even daytime running lights, which have been estimated to use up to a tenth of gallon of fuel, aren't considered.
The depletion of fuel isn't measured directly in this testing, either, and test vehicles don't use gasoline.
They operate on a special laboratory fuel called indolene clear. It's a test fuel that's free of the variability in quality that can be found in gasoline, and it has just eight carbon atoms.
As the vehicles run, emissions are collected from the tailpipes. Because the carbon content of the fuel is known, technicians calculate fuel economy by measuring the carbon compounds expelled in the exhaust.
Automakers conduct the tests, using pre-production prototypes of their upcoming new vehicles, the EPA said. You can bet they make sure that anything that would lessen fuel economy—such as underinflated tires, misaligned wheels and poorly tuned engine—are fixed before the test.
The EPA, which announces the top vehicle in fuel economy for each new model year, does its own testing in its own lab—to confirm the numbers from the automakers—on only 10 percent to 15 percent of new models.
Lab vs. Real World
Acknowledging that lab conditions don't reflect what drivers encounter in the real world, the EPA does allow the lab figures to be adjusted.
The laboratory city value is multiplied by 0.90 and the highway value is multiplied by 0.78 after an agency study several years ago reported drivers on the roads get 90 percent of the EPA's city figure and 78 percent of the highway figure.
But there are still plenty of drivers who complain they don't get anywhere near the official figures. This fact and the Bluewater Network petition have forced the EPA to look at updating these figures.
The EPA isn't going to change the underlying emission test procedure. But it is considering more aggressive adjustment figures for city and highway mileage in the hopes of putting out more realistic fuel economy numbers by the 2008 model year.
"The bottom line is in the real world, [fuel economy] is variable," said one official at General Motors Corp. "In general, all the different things that can affect fuel economy tend to make those numbers lower [than the EPA's]."
What Affects Fuel Economy?
Weather conditions, aerodynamic drag as a vehicle moves through the air, use of accessories, tire inflation and wheel alignment, the tuning of the engine, how much weight a vehicle is carrying, its speed and a driver's habits all play a role.
For instance, driving up a mountain road with a 7 percent grade can cut fuel economy by as much as 25 percent.
If tires aren't properly inflated, fuel economy can be cut by up to 6 percent, and misaligned wheels also decrease fuel economy, said one Ford engineer.
And drivers who manage their driving habits—accelerating gradually, driving smoothly and with care - can boost fuel economy as much as 20 percent compared to a more aggressive driving style, the EPA says.
Using the Rating
Is there any reason to look at the fuel economy numbers on the window sticker?
Yes. They can be a decent "relative measurement" for vehicle comparisons.
Since all automakers use the same procedure, the numbers can be compared from one kind of vehicle to another to help shoppers get a relative sense of which vehicles are more fuel-efficient.
But remember, there's no guarantee that a driver will reach an exact fuel economy number.
And don't forget the fine print. Every window sticker also states the range of fuel economy that's expected in a certain vehicle segment.
It's in smaller print on the label. On a 2006 Ford Explorer 4X4 with V8, for instance, the label states that the city driving range could be as low as 11 mpg and as high as 17 mpg. Meantime, the big, black number on the sticker that catches a shopper's eye says city mpg is 14.
The posted highway mileage for the same Explorer is 20 mpg. But the range, in the small print, says it could be as low as 17 mpg or as high as 23 mpg.
And to be fair, even the biggest fuel economy numbers come with a caveat printed right by them: "Actual mileage may vary with options, driving conditions, driving habits and vehicle's condition."
How to Get This Info
Readers can find official fuel mileage numbers at the government's Web site at www.fueleconomy.gov
It's easy to compare vehicles. Once you're on the Web site, click "Find and Compare Cars." There, at the left, you will be able to select a list of vehicles by their market class, which is basically the broad sales categories they fit into, or their official EPA size class.
So, if you're shopping for an SUV, you can get a list of market SUVs that shows the highest-to-lowest fuel economy numbers, by model.
The EPA's fuel economy Web site also maintains mileage numbers for vehicles going back to the 1985 model year. So, it can be something of a reference for people buying used cars, except consumers need to remember that the archival fuel economy figures were derived from the vehicles when they were brand new.
An older vehicle's current condition and maintenance over the years has a lot to do with the kind of fuel mileage it gets today. In other words, don't expect that bargain-priced 1987 Cadillac Allante that's on the used-car lot to get the 16/24 mpg that it was rated at when it was a new car.
Consumer Reports' Figures
There is another good source of mpg information: It's the well-known Consumer Reports magazine.
Officials at CR provide their own combined city and highway fuel economy rating for each vehicle they've tested recently.
Unlike the government ratings, CR's figures are based on real-world experience.
The downside: CR doesn't have mpg figures for all models, the way the EPA does, and CR only provides a combined figure, not a breakdown of city and highway ratings.
See Consumer Reports' study
on cars with the best and worst in overall economy.
Improving Performance of Your Car
Remember, you don't have to be a frustrated bystander as the needle dips to "empty." Even an older car can get better mileage with some help.
First, make sure your vehicle is in tip-top form, because a poorly tuned car can use more fuel than a vehicle that has been properly maintained.
How much more? According to AutoZone, an auto parts store, a new oxygen sensor alone can improve fuel economy by up to 15 percent.
As mentioned, tires need to be checked often for proper inflation, especially in areas where punishing blows from potholes can adversely affect tire pressure.
The nasty potholes can cause wheels to get out of alignment, too, which can reduce fuel economy by up to 10 percent.
Clean out your car and get rid of extra, unnecessary weight, such as sports equipment or heavy tools that you may not need to carry around with you. AutoZone estimated that an extra 200 pounds of weight can reduce a vehicle's fuel economy by 1 mile per gallon.
Drive more smoothly, avoiding jackrabbit starts that can waste fuel.
Look down the road as you drive, safely modulating your car's speed so you flow with traffic and don't have to stop, then accelerate, repeatedly. Aggressive driving is estimated to reduce fuel economy by up to 20 percent.
When you can, plan your travel to take advantage of times when roads are least congested. This will lessen your drive time.
If you're going to someplace new, get directions ahead of time so you don't waste time-and fuel-driving around trying to find your destination.
Ann Job is a freelance auto writer.