Citroën superminis guzzle 23% more petrol than claimedPetrol engine superminis mpg compared

01 July 2015

You may well buy a supermini with fuel saving in mind. But did you know that the miles per gallon (mpg) figure you see in adverts isn’t always accurate?

Our testing has shown that some petrol engine superminis – including the Citroën C1 and Hyundai i20 – are 20% less fuel efficient than claimed, costing owners up to an extra £220 per year.

In fact, only superminis from five brands – Honda (5%), Dacia (13%), Chevrolet (13%), Vauxhall (13%) and Seat (14%) – came within 15% of the mpg you’d expect if you took the official fuel economy figures at face value.

EU law requires carmakers to show official test figures in their adverts to help consumers compare fuel economy between different models. But we think the figures should also reflect real-world driving – and if a brand quotes an mpg figure in its adverts, a consumer should be able to achieve it in normal use.

That’s why it’s vital the EU test is updated to be more accurate in 2017 as planned, and not delayed to 2020 as some manufacturers would prefer.

Come clean on fuel claims - sign our petition for fuel claims you can trust.

Petrol superminis – claimed vs actual miles per gallon (% difference)

@inlinemarker@ Superminis MPG @inlinemarker@

Which cars were included in the study?

The medium cars category is an industry-standard class including the likes of the Ford Fiesta, Volkswagen Polo, Chevrolet Trax, Citroën C1, Dacia Logan, Honda Jazz, Nissan Note, Peugeot 108, Renault Clio and Vauxhall Mokka.

How we test MPG

The testing that underpins every Which? car review is designed to give consumers the most accurate picture possible of how their car will perform in everyday life. So when assessing fuel economy, unlike the official EU test, we include a motorway driving simulation, switch on the lights and air con, and inflate tyres to the recommended pressures.

And if a car has different driving modes available, we use the one it starts up in by default, rather than switching to an 'eco' mode. This may offer better economy, but will also often neuter a car’s performance to the point where it’s awful to drive.

What's the problem with EU mpg measurements?

Don’t be fooled by the name of the official driving simulation currently used to calculate mpg figures – the New European Driving Cycle (NEDC) hasn’t been new since it was last updated in 1997, and the basis of the test was first introduced in the 1970s.

The test’s lack of real-world driving scenarios and numerous loopholes make the figures it generates unachievable when you get behind the wheel of a car.

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