Car fuel economy: will new test make claimed mpg easier to achieve?

Car fuel economy

Volkswagen claims its Golf Bluemotion can do 88.3mpg. Drivers struggle to achieve that in the real world but it isn’t VW’s fault (Picture © Volkswagen)

Car fuel economy is one of the things drivers complain about the most. It’s not that modern cars aren’t economical. They are. But car makers claim they’re much more frugal than is actually the case. The reason for the inaccuracy is all down to the way car economy is tested. But that is about to change. So, are we likely to see cars finally living up to their makers’ consumption claims? 

Car fuel economy: What is the new test?

All cars have their fuel consumption measured by the same, independent test. From 2017 onwards, cars will have their economy measured by the Worldwide harmonized Light vehicles Test Procedures (WLTP). It will replace the New European Driving Cycle test that is currently used. Like its predecessor, the WLTP is still a laboratory based test and doesn’t include any actual driving.

Car fuel economy: Will it be any more accurate?

This is the big question. According to independent testing company Emissions Analytics, the WLTP will narrow the distance between ‘official’ and reality – but not by much. Emissions Analytics boss Nick Molden said: “We believe the WLTP will close the gap by half. So there will be on average a 14 per cent discrepancy between claimed and true mpg. But that is best case scenario and others think it will be worse than that.”

Car fuel economy: How bad is the current test?

Independent testing has found that on average makers’ claimed mpg is 24 per cent better than in real life. That means if the manufacturer claims your car does 60mpg, you can expect to get 45.6mpg from it. The knock-on is that car owners are spending on average £133 a year more on fuel than they thought they would be. And as car makers come up with ever more ingenious engineering methods to make their cars more economical, that discrepancy increases, by 2 per cent a year according to testing company Emissions Analytics. By 2017, we’ll be looking at a 28 per cent average gap between the New European Driving Cycle (NEDC) and reality.

Car fuel economy: Why is the current test so bad?

Part of the problem is that the NEDC is neither new – it’s been around for more than 40 years – and it doesn’t involve driving as it’s all done on a rolling road in a lab. Testing by consumer organisation Which? found that 98 per cent of the cars it tried couldn’t match or beat their makers’ mpg claims.

Car fuel economy: Doesn’t the test ensure a level playing field?

The aim of the NEDC is to give customers some kind of bench mark so that they can assess different cars against each other. However, some areas of the rules are open to interpretation and while all car makers abide by the letter of the law, some interpret its spirit differently. For example, makers can improve their cars’ mpg by disconnecting the alternator, turning off the air-conditioning, using special lubricants and over inflating tyres. If they don’t do any of these, they put themselves at a competitive disadvantage against their rivals.

Car fuel economy: Why can’t they come up with accurate tests?

Another big question. The new WLTP test was dreamt up by the United Economic Commission for Europe. It’s not an organisation short of brain power or resources. However, Nick Molden believes it’s missed a trick: “The regulator should monitor whether or not cars deliver the claimed economy in the real world,” he said. “And I would make the cycle more aggressive still to replicate day-to-day driving.”

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