By Jim Kerr

Join any conversation about vehicles and sooner or later the topic of fuel economy comes up. Some drivers claim excellent fuel economy, while others cry about the poor fuel economy they are getting. These can even be on the same model of vehicle! Driving style, driving conditions and vehicle condition all play an important part in determining the fuel economy you can achieve with your vehicle – but what if you are buying a vehicle and want to compare fuel economy between different vehicles? That’s where the Natural Resources Canada EnerGuide is helpful.

NRC’s EnerGuide lists fuel economy ratings and annual fuel costs for light duty vehicles sold in Canada. Heavy duty vehicles, those over 8500 pound Gross Vehicle Weight Rating (GVWR) are not rated. Using a simulated city and highway drive cycle on a dynamometer, fuel economy is calculated by measuring the amount of hydrocarbons emitted from the tailpipe. While these ratings are useful in comparing one vehicle’s economy to another, they have one serious flaw: they don’t represent real life.

The testing procedures used by Transport Canada for fuel economy during city driving are done in a warm climate – 20 to 30 degrees C. A 12-kilometre drive is simulated, with a top speed of 91.3 km/h but an average speed of only 32 km/h. It also includes 18 stops and 220 seconds of idling time.

The highway drive cycle is also done in 20 to 30 degree temperatures. The vehicle hits a top speed of 96.5 km/h but averages only 77 km/h over a 16-kilometre drive cycle. Acceleration during both drive cycles is slow to moderate.

It is rare for a driver to operate a vehicle under these conditions, so fuel economy ratings are typically better than actual mileage achieved by everyday drivers – so they are really only useful when comparing vehicles.

In the United States, the EPA (Environmental Protection Agency) has been using a similar test, although the test results are not used as U.S. fuel economy ratings. The EPA recognized that there was a difference between test data and actual real life fuel economy, so they added in a compensating factor to the fuel economy ratings. I call it the fudge factor – it helped bring the fuel economy ratings closer to reality, but only if you drove sedately in warm weather. Because of this “fudge factor” the reported EPA fuel economy and the Canadian EnerGuide ratings show different fuel economy for the same vehicle. It also meant you couldn’t convert the U.S. miles per gallon economy figures to Canadian litres per 100 kilometres and still have a rating that you could compare to other Canadian ratings. Now things are going to get even further apart.

For 2008, the EPA is changing the way U.S. car fuel economy is tested. Three additional tests will be added that represent more realistic driving conditions. One of the tests will be with the vehicle air conditioning turned on during a 95 F (35 C) outside temperature drive cycle. The test will last for nearly 10 minutes.

Another test will simulate cold weather driving, with the engine started cold and then driven for 31 minutes with an outside temperature of 20 degrees F (minus 7 C). It will include 23 stops and an average speed of 20 mph (32 km/h).

The third additional test is a higher speed test conducted with a warm engine on a normal summer day temperature of 68 to 86 F (20-30 C). It will include a top speed of 80 mph (129 km/h) and an average speed of 48 mph (77 km/h), but perhaps the biggest difference is the faster acceleration and aggressive braking rates used during the test.

There are more specific criteria for all the drive cycle tests, but those are the key additions. Fuel economy will now be calculated with five different drive cycles, and the numbers will be closer to real life because of the additional tests.

The new EPA methods for estimating vehicle fuel economy will apply to model year 2008 and later vehicles. Even with the improved testing procedure, estimates will still be adjusted downward to account for factors that are difficult to replicate in a laboratory, such as wind and road surface resistance.

There is no word of Canadian test procedures changing so that they will represent more accurate fuel economy, so we will just have to compare one Canadian vehicle rating with another, and not compare them to U.S. fuel economy ratings.

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