Article by Mark Stevenson

When someone enters a dealership looking to purchase a new vehicle, fuel economy tends to be on the mind of most consumers. Prices for regular 87-octane gas have been north of $1.00/L for quite some time now. And, with more stringent CAFE requirements looming in the future, automakers are trying to do everything they can to boost fuel economy numbers for their newest cars and trucks.

The window sticker – a piece of paper affixed to the side window of a new car – contains a cornucopia of information with relation to equipment, options packaging, origin, and price. But, the tidbit that gets the most attention (after price) is the large fuel economy number, printed in stark black next to the EnerGuide stamp of approval.

In a recent article published by CBC News, a couple from Calgary purchased a new 2011 Chevrolet Cruze – equipped with a 1.4L turbocharged engine and automatic transmission – rated for 5.5 L/100 km on the National Resources Canada highway testing cycle. Farah Mocquais and her husband, Pierre-Yves, purchased the car expecting to get exactly or close to the stated fuel economy during Mrs. Mocquais’ two-and-a-half-hour commute from Calgary to Lethbridge.

However, as most of these fuel economy stories go, the couple stated the vehicle “consistently showed it used 8.5 litres per 100 kilometres,” a difference of 3.0 L/100 km.

They have every right to be shocked. Or do they?

Fuel Economy ExpectationsFuel Economy ExpectationsFuel Economy Expectations
Fuel Economy Expectations. Click image to enlarge

The Window Sticker

On all window stickers for passenger vehicles in Canada, regardless of manufacturer, fuel economy numbers are displayed. These numbers are generated using an old testing system governed by Natural Resources Canada, the body that oversees the EnerGuide Fuel Consumption Guide.

While automakers are not required by law to use the numbers stated in the Fuel Consumption Guide on their window stickers, a memorandum of understanding exists between the automakers and government to use their testing system for inclusion in the guide, giving the numbers an “apples to apples” comparison with other vehicles.

The testing procedure – called “two-cycle testing” – consists of a city test and a highway test.

From Natural Resources Canada:

Fuel consumption values are derived from the emissions generated during two laboratory driving cycles – a city test and a highway test.

The city test simulates urban driving in stop-and-go traffic with an average speed of 34 km/h and a top speed of 90 km/h. The test runs for approximately 31 minutes and includes 23 stops. The test begins from a cold engine start, which is similar to starting a vehicle after it has been parked overnight during the summer. The final phase of the test repeats the first eight minutes of the cycle but with a hot engine start. This simulates restarting a vehicle after it has been warmed up, driven and then stopped for a short time. Over five minutes of test time are spent idling, to represent waiting at traffic lights.

The highway test simulates a mixture of open highway and rural road driving, with an average speed of 78 km/h and a top speed of 97 km/h. The test runs for approximately 13 minutes and does not include any stops. The test begins from a hot engine start.

The fuel consumption values derived from these tests cycles are adjusted upwards by 10% (city) and 15% (highway) to more accurately reflect real-world results.

Fuel Economy Expectations
Fuel Economy Expectations. Click image to enlarge

Focusing on the highway test above, as that is what is usually quoted in advertising and of dispute between Mr. and Mrs. Mocquais and General Motors Canada, there are other criteria that must be met during the test, such as a test cell temperature of between 20 and 30 degrees Celsius, distance of 16.5 km, warm engine start, and an average speed of 78 km/h. However, two additional criteria – a top speed of 97 km/h and maximum acceleration of 5.2 km/h per second – are not typical of how we drive our cars in real life. Using the test criteria, it would take almost 19 seconds to reach the maximum speed.

“The EnerGuide two-cycle system is based on driving the speed limit. Garry (Sowerby) and Lisa (Calvi) drove across the country in a diesel (Cruze), rated for 4.2 litres per 100 kilmetres, and they got 4.3 litres per 100 kilometres on average,” explained George Saratlic, Product Communications for General Motors Canada, in a phone interview.

“But, that’s driving at the speed limit or just below it. Most people don’t drive at the speed limit or just below it.”

It should also be mentioned the highway test does not include any stops or idle times, unlike the city test which includes 23 stops and 18 percent idle time.

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