Some new cars are more than 25 per cent less fuel efficient than official testing suggests, according to new research.
A comparison of official WLTP figures against data collected in independent laboratory testing found that on average new models are 6.3 per cent less economical than stated but that performance varies widely between vehicles.
While some under-performed by as much as a quarter, other cars performed almost 20 per cent better than the official figures.
Manufacturers are obliged to publish official economy data based on the Worldwide Harmonised Light Vehicle Test Procedure (WLTP) which carries out lab-based economy and emissions testing on all new cars. However, consumer site What Car? carried out its own lab testing designed to more accurately reflect real world driving.
It found that the BMW 420d M Sport Pro Edition achieved 26.4 per cent lower fuel economy than its WLTP test figure, returning “real world” economy of 42.4mpg against a WLTP figure of 57.6mpg. The Suzuki Swace 1.8 Hybrid, which is based on the Toyota Corolla, was the second worst performer, with a 21.6 shortfall (50.2mpg compared with 64.2mpg).
Best-sellers including Ford’s Fiesta and Focus, the BMW 3 Series and Audi A3 also fell between 15 and 20 per cent short of official figures.
At the opposite end of the scale, Ford Ranger Thunder 2.0 achieved 18.9 per cent better fuel economy than its official figure, and the Honda CR-V Hybrid 2.0 performed 12.3 per cent better, ahead of models from Volkswagen, Dacia and Skoda.
Steve Huntingford, editor of What Car?, said: “From SUVs to small hatchbacks, our True MPG test results show there are still significant differences between the claimed and actual fuel economy figures of many models.
“So it’s important for buyers to do their research before they buy. Our True MPG tool is unique to the industry and gives new car buyers an accurate idea of their vehicle’s real world fuel economy.”
To achieve the real-world economy figures, the fuel tests were conducted on a rolling road, under strictly controlled laboratory conditions to simulate real world driving styles. What car says the tests are repeatable within one percentage.