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A gas nozzle is used to pump petrol at a station in New York February 22, 2011. (SHANNON STAPLETON/REUTERS)
A gas nozzle is used to pump petrol at a station in New York February 22, 2011. (SHANNON STAPLETON/REUTERS)

You & Your Car

How fuel economy numbers are determined Add to ...

I read where a couple in Calgary is suing General Motors because their Chevrolet Cruze’s real-world mileage is vastly different than the manufacturer’s stated fuel economy. How are auto makers able to make these claims? – Don

Manufacturers report mileage numbers under conditions spelled out by Natural Resources Canada (NRC) – which, in turn, are a copy of those instituted by the U.S. Environmental Protection Agency (EPA).

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The government does not actually conduct the tests of the hundreds of different vehicles and drivetrain combinations; it relies on manufacturers to obtain and submit the numbers according to a strict set of test procedures. On rare occasions, audits reveal these numbers to be wrong and the manufacturer is publicly identified and the numbers changed.

For example, Hyundai and their sister company, Kia, are reimbursing customers millions of dollars after the EPA determined their fuel consumption test results were inaccurate.

The problem is that the conditions under which the mileage numbers are obtained bear little resemblance to real-world driving. NRC admits as much by saying the numbers should be used for comparison purposes, i.e., comparing one vehicle with another. The test procedures includes two driving cycles – city and highway. They are conducted at temperatures between 20 C and 30 C – including the initial “cold” start – hardly an average situation in Canada. The city portion includes 18 kilometres of driving, including 23 stops, five minutes at idle, slight acceleration, a maximum speed of 90 kilometres an hour and an average speed of 34 km/h.

The highway portion includes slightly less than 17 kilometres with a top speed of 97 km/h and an average speed of 78 km/h. This, too, includes only slight acceleration. All of this conducted at the same room temperature on flat surfaces.

Following an initial outburst by consumers and complaints from dealers, the city numbers were “adjusted” upward by 10 per cent and the highway ones by 15 per cent in an attempt to address the discrepancy.

If you and the owner of that Cruze were to drive in the manner used in the tests, there is no doubt you could achieve the mileage claims advertised by the manufacturer.

But the problem is worsened by the fact Canada did not follow the United States in 2008 when it added three additional cycles to the procedure. These changes included provisions for cold starts and running at ambient temperatures below freezing, hot starts and running at high temperatures with the air conditioning on, speeds up to 130 km/h and harder acceleration.

Obviously, the American ratings are closer to real-world conditions. But Canada has not followed suit.

Blame the federal government – not the manufacturer.

If you have questions about driving or car maintenance, please contact our experts at globedrive@globeandmail.com.

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