Glossy sales brochure quotes frugal economy figures - then you buy the car and find you’re visiting the fuel station more frequently than advertised.

Johannesburg - The difference between the factory-quoted fuel consumption of cars and their real-world economy has been a long-running source of controversy.

You know the story: the glossy sales brochure quotes appealingly frugal economy and emission figures for a car, only for you to get a rude awakening when you buy the car and find you’re visiting the petrol station more frequently than advertised. Not only that, but your car’s also belching more pollution into the air, as emissions are directly related to fuel consumption.

It’s not that the car companies are specifically trying to fool you, as they’re quoting fuel-consumption figures gleaned from independent laboratory tests such as the New European Driving Cycle used in Europe and other parts of the world, which puts vehicles through a standardised driving cycle. It’s just that these lab tests have about as much to do with real-world driving as polony has to do with healthy eating.

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The infamous ‘Dieselgate’ scandal of 2015 brought the issue firmly into the spotlight when Volkswagen was caught cheating its emissions figures by installing 'defeat devices in 11 million diesel cars that made them seem far less polluting during lab tests than when driven on the road. In the wake of the scandal Peugeot-Citroen group PSA announced it was turning over a new leaf and would henceforth be conducting more relevant fuel-consumption tests on its diesel cars, driving them much like you and I would during normal commuting.

As expected, these new tests showed cars were much thirstier than in the official NEDC evaluations. For instance, a Peugeot 308 used five litres per 100km, compared to just 3.2 in the NEDC tests; a Citroen C4 Picasso MPV drank 5.6 litres versus four litres; and the Citroen DS3 used 4.9 litres compared to 3.6 in the NEDC laboratory.

Kudos to PSA for tying to win back some customer trust in the motor industry in the wake of Dieselgate.

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There has been no mass movement by the motor industry to follow PSA’s lead, but car companies will in any case now be forced to publish more realistic fuel figures by the soon-to-be-introduced Worldwide Harmonised Light Vehicles Test Procedures (WLTP). 

Major car-producing regions including the European Union, the Unite States, India and South Korea drew up the WLTP standard in 2014 as a global test cycle so that pollutant and CO2 emissions as well as fuel consumption values can be comparable worldwide. WLTP, which will be rolled out internationally from September 2018, was developed using real-driving data gathered from around the world, and will better represent what’s achievable in normal driving conditions by you and I on our daily commutes.

The new test has a higher average speed of 46.6km/h compared to 33.6km/h in the NEDC cycle, and will also use vehicles fitted with all their available options, making them heavier than the cars which were previously tested without all their extra kit. This new test is expected to return fuel-consumption figures around 20 higher than those reported under the NEDC, which will narrow the gap to what’s real-world achieveable by car customers.

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The disconnect between claimed and real fuel-consumption figures has landed some companies in hot water, including Ford South Africa which in 2014 was forced to withdraw an internet advertisement that misled the public about the economy of its EcoSport crossover vehicle. The ruling - one of several that the Advertising Standards Authority made over the same issue - found that Ford’s advert didn’t sufficiently inform motorists that the quoted consumption figures were obtained in controlled lab conditions and thus weren’t realistically attainable by customers.

It involved an EcoSport 1.0T owner who averaged around 8.6 litres per 100km, well above the advertised 5.7 litre consumption figure, and the ad didn’t feature the standard disclaimer pointing out the discrepancy between laboratory and real-world figures. In it ruling the ASA referred to earlier similar cases including a ruling in a 2012 case brought by a Volkwagen Polo owner, where it stated that “standardised tests are invaluable in ensuring that potential buyers can compare fairly across manufacturer ranges, but the consumption figures claimed must make it clear whether or not they were achieved in ‘the real world’ or under testing (laboratory) conditions.”

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It’s important to understand that a car’s fuel consumption isn’t constant and can vary substantially dependent on factors like driving style, road and traffic conditions, and weather, but the new WLTP tests should at least bring more semblance of reality.

We're in the business of road testing vehicles and our own experience concurs that actual fuel consumption figures are almost always higher - sometimes vastly - than manufacturers’ claims. For this reason our articles list the actual figures we attain in our test drives, in order to give our readers a more realistic picture.

If you’re looking to buy a new car, an archive of all our road tests (with fuel figures) can be found at www.motoring.co.za to help you along.

Drive360

Follow Denis Droppa on Twitter @DenisDroppa