New cars are 5.4% less efficient than WLTP figures suggest, says What Car?

New petrol, diesel and hybrid cars are, on average, 5.4% less efficient than their official WLTP fuel consumption figures suggest, according to new research by What Car?.

It tested 56 new models under its independent True MPG test, to determine its real-world fuel economy. The figure was then compared to the manufacturer’s claimed figure.

On average, vehicles were 5.4% less efficient than the WLTP figures suggested, but the research revealed significant differences between models.

The worst performers were found to be more than 20% less efficient than their official figures, while the best performers were found to be 15% more efficient.

The tougher and longer WLTP emissions and type approval test was introduced in 2017 by the European Commission and became mandatory for all new vehicles from September 2018 onwards. The WLTP test replaced the previous New European Driving Cycle (NEDC) type approval test, which dated back to the 1980s, with the aim of providing more accurate fuel consumption figures for new car buyers.  

The new WLTP test is significantly more accurate than the NEDC test, according to What Car?’s figures. In a previous study of 159 vehicles tested under the NEDC protocol, there was an average discrepancy of 20.2% between True MPG and the manufacturer quoted figures - with the worst performers as much as 40% less efficient than advertised.

Steve Huntingford, editor of What Car?, said: “For years, most buyers have taken the official fuel economy figures with a grain of salt. Our research shows that while the latest test is more accurate, there are still large differences on some makes and models, which is why it’s important for buyers to do their research before buying.”

What Car? publishes its True MPG data on its website.

Worst real-world MPG performers:

Best real-world MPG performers: