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Why do car fuel economy specs differ so much per country?

The Insight 2010 fuel economy numbers showed big differences per country. According to Japanese and European testing standards the Insight is more fuel efficient than the Civic Hybrid. Yet according to Canada and US standards it’s less fuel efficient. Also European numbers show consistently 20%+ higher fuel economy numbers. Do European drivers drive more fuel efficient:-)? Which is more realistic?

Let’s take the Insight as an example showing the different test method ratings:

Differences are pretty big. Here are the same results in a table with % differences:

 

US EPA

Europe ECE

Japan JC08

Japan 10-15

% to EPA

City

40 mpg

51 mpg

 

 

+28%

Highway

43 mpg

56 mph

 

 

+30%

Combined

41 mpg

53 mpg

61 mpg

71 mpg

+29% / +49% / +73%

Let’s take a quick look on the different testing methods from US, Europe and Japan:

Test method

Avg speed

Max speed

Distance

EPA City*

21 mph / 34 km/h

58 mph / 83 km/h

11.0 mi

ECE City

12 mph / 19 km/h

31 mph / 50 km/h

2.5 mi

10 Mode City

11 mph / 18 km/h

25 mph / 40 km/h

0.4 mi

 

 

 

 

EPA Highway*

48 mph / 77 km/h

60 mph / 97 km/h

10.3 mi

ECE Extra Urban

39 mph / 63 km/h

75 mph / 120 km/h

4.3 mi

10-15 Mode**

14 mph / 23 km/h

43 mpg / 70 km/h

4.2 mi

JC08 Cycle**

15 mph / 24 km/h

50 mph / 80 km/h

5 mi

* 3 additional tests are done to adjust the numbers (70mph, AC, cold start)
** Combined mode 

You can see that the average speeds for the EPA test method are clearly higher which explains part of the lower fuel economy numbers. Also note that the acceleration in the EPA test is much higher. See Edmunds article below for more detailed test info.

 

Conclusion

Which one is more accurate depends on driver style and route being driven. Not sure if the test methods try to reflect a generalized route and driver style. But either way it’s generalized and one size doesn’t fit all. I would say though that the European and Japanese methods are rather indication which fuel economy is possible under good circumstances. Whereas the US is a bit more pessimistic and closer to reality. In general I beat typically EPA 10-20% so for my case it’s between EPA and ECE test method.

 

Additional Details testing methods:

UPDATE: For more info on New European Driving Cycle (NDEC) see here: http://www.dieselnet.com/standards/cycles/ece_eudc.html
UPDATE: Car & Driver technical article on EPA testing: http://www.caranddriver.com/features/09q3/the_truth_about_epa_city_highway_mpg_estimates-feature

USA EPA 2008+:

City:

Highway:

To make it more complex EPA also adds 3 additional tests to adjust these numbers. See http://www.fueleconomy.gov/feg/fe_test_schedules.shtml for more info.

European 2004/3/EC urban / extra urban cycle mode:

 

Japan 10-15 mode:

 

Japan JCO8 Cycle:

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