Car manufacturers use official miles-per-gallon figures to promote their most efficient models. Yet our recent head-to-head test found that some ‘eco’ cars’ mpg ratings are way off the mark with everyday motoring.
Our research shows that rising fuel prices are one of consumers’ top financial concerns. So making sure you buy a car that doesn’t guzzle petrol or diesel is a higher priority than it ever has been before.
As a result, ultra-efficient small cars have become extremely desirable. The current range of ‘eco’ cars available that claim to emit less than 100g/km of CO2 seem to be the models to choose from, as they also mean free car tax and exemption from the London congestion charge.
Miles off the mark
Worryingly, of all the cars we tested in 2012, the ultra-efficient small cars showed the greatest difference between our own mpg tests and the EU tests used by manufacturers.
In fact, all 10 of the cars with the largest disparity between claimed mpg and our test results are ‘eco’ models that claim to beat the 100g/km CO2 emissions mark. Seven of these 10 claim to achieve more than 70mpg – but our test reveals this isn’t always the case.
The worst is the Peugeot 208 1.4 e-HDi EGC automatic, which our test found to be an astonishing 21.7mpg short of the claimed mpg. It’s still a highly efficient car, but the difference between the EU test of fuel consumption and ours could cost drivers £327 a year in petrol.
However, the biggest cost difference revealed by our tests came from the Fiat Punto TwinAir at £366 a year. The disparity between mpg ratings wasn’t as large, but because the tested mpg was the lowest of all, you’ll have to fill the Fiat more often than the others.
What’s the difference?
One reason for the large disparity between the figures is the difference in our own test cycle compared to the EU cycle that manufacturers use for their official claims.
Like our test, the EU test uses rolling roads. However, unlike EU tests, we use the same rolling road in our lab for all cars to make sure results are directly comparable. We also test any cars with adaptable settings (eco mode, sport mode, town mode) in the default mode the car starts up in – unlike the EU test, which uses the most economical mode.
On top of this, our urban and extra-urban test cycles are conducted from both a cold and warm start and then averaged. It also includes a section of motorway-speed driving. Finally, our mpg figure combines the urban and extra-urban test, together with the motorway test, weighted 70:30. All of these factors make our tests very robust.
Do you know how close you are to actually achieving the official mpg figure for your car? How important is the mpg rating to you when choosing a car?
Can you match your car's mpg claims?
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