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Originally Posted by sfax
I agree which is why I like my own personal suggestion of quoting a 20 minute drive at a constant speed of 50, 60, 70, 80 (same course, some hills) and a round town stop-start route and then taking an average for basic comparisons from one model to another, and if someone wants to get more detail they can drill into the individual speed tests.
If the implications of "correcting" the mpg on CO2 are so grave, then that only goes to prove how that the CO2 figures are misleading too
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EPA in the USA revised their test regime, for the same reason as we have issues over here. But when you see all the data and how they arrive at the results it a complex exercise. Problem is it still has to be done in controlled conditions to get exact data, as it is based on a “composite” calculation of all five tests. To quote a part of ththe EPA explanation...
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.....external conditions impact fuel economy on a trip-to-trip basis, they do not change the laboratory test result. Therefore, a repeatable test provides a level playing field for all vehicles, which is essential for comparing the fuel economy of one vehicle to another. Finally, EPA must preserve the ability to confirm the values achieved by the manufacturers’ testing, and this can only be achieved with a highly repeatable test or set of tests. No other fuel economy test program provides the level of repeatability as the EPA program.
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The European test is also a level playing field, but it just doesn't have the scope to reflect real world driving. Something like a simple motorway 70mph constant speed test, albeit controlled for repeatability of any vehicle, would add a very useful bit of data for determining what each vehicle achieves on the typical motorway cruise. Would show up the "good and bad", compared to the existing combined published figure, which many feel they should achieve.
The problem with CO2 levels, the manufacturers are working to targets for average levels by fixed dates, any change to the test regime will completely blow those targets away, or the politicians will need to review and amend the whole target structure. No one wants mud on the face, so it seems to get put on the back burner, even though there are noises to make the tests more realistic.
HighlandPete