Q. Official fuel consumption figures for my Audi mostly tally with what it achieves. I’m now looking for a new car, but I’m worried by media reports of the inaccuracy of official figures. I don’t want to buy a car with an official figure of 70mpg only to discover it returns 50. Whom can I trust?
AM, Murthly, Perthshire
A. All cars sold in Europe are subject to the New European Driving Cycle (NEDC) fuel consumption test, and car makers have to publish the test results as the official mpg figures for their cars.
While this helps buyers to compare cars, the figures often bear little relation to real-world consumption. This is partly because the test was devised in the 1970s, when cars were different, and partly because features of real-world driving such as hills are not simulated in the test.
In the past car makers have been accused of manipulating testing methods to favour their vehicles. In a survey the International Council on Clean Transportation found that real-world mpg is typically 21% lower than the official figures — up from 8% in 2001.
The NEDC will be replaced by a more accurate test, but not for at least three years. For the time being, buyers have to rely on the unofficial results reported by motoring organisations and the media.
Emissions Analytics, a testing firm, calculates fuel economy for What Car? magazine by driving cars on a set route and standardising the figures to allow for weather conditions and traffic.
Audi claims that these tests show its cars to be among the best for matching the official figures, but there are still big differences between models. Some fall short of official figures in real-world driving by more than 10%.
Results show that it’s often the supposedly ultra-efficient cars that disappoint the most. The Toyota Prius has a claimed figure of 70.6mpg but What Car? records its average real-world consumption as 52.2mpg. The Volkswagen Golf 1.6 TDI Bluemotion, officially rated at 68.9mpg, recorded a real-world 51.8mpg.
Before you buy a car, arrange to take it for an extended test drive so you can get an idea of how much fuel it uses over familiar routes.
Emma Smith is a journalist specialising in consumer issues and is a regular Driving contributor – read more from Emma here.
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