How Motor Manufacturers Could Manipulate MPG Tests
Motor manufacturers could manipulate tests to produce lower fuel consumption and emission figures than motorists typically manage on the road, a pressure group has claimed. Transport & Environment has, therefore, revealed the techniques manufacturers could – but do not necessarily – use to maximise efficiency. These include placing tape over bodywork indentations to minimise aerodynamic drag, changing the wheel alignment to reduce rolling resistance, utilising highly efficient tyres, installing lubricants which improve engine efficiency and disconnecting the alternator. Realigning the brake pads can help too. Despite these techniques manufacturers have – according to the RAC – claimed that “laboratory tests offer a controlled base for consumers to compare models more effectively than real world driving conditions”. The RAC has also revealed that a new car typically averages 56.5mpg whereas the pressure group estimates 45mpg is more realistic. Either way, new tests from 2017 should ensure figures accurately represent ability. Clearly, it is in manufacturers' best interest to achieve the best possible test results. These, of course, help attract customers. Furthermore, forthcoming rules will ensure that a company's fleet must – on average – emit carbon at a rate no higher than 130g/km by 2015. Many hit this target already – some by creating zero emission electric cars as a means of counteracting their more polluting models. Clever, but perhaps sneaky.
How Fuel Consumption Is Calculated
As things stand, a car's fuel consumption figures – assuming it has a traditional internal combustion engine - are calculated via the urban/extra-urban tests. These are performed once it has covered at least 1,800 miles so the engine is properly run-in, i.e. at its most efficient. The urban test is performed on a rolling road in a laboratory that has an ambient temperature of 20°C to 30°C. Furthermore, the vehicle must have been stationary for several hours so that the engine is cold. The test requires the subject to perform a series of accelerations and decelerations. It must also maintain consistent speeds and idle while stationary. Within these manoeuvres the vehicle's maximum speed is 31 mph, it averages 12 mph and covers 2.5 miles. In contrast, the extra-urban test represents faster routes such as a-roads. This is performed immediately after the urban test and once again includes a series of accelerations/decelerations, etc. However, the vehicle's speed rises to 75mph and it averages 39 mph over 4.3 miles. The combined figure is then calculated based on cumulative results. Such figures – despite the justified concerns – can be achieved away from the laboratory in certain circumstances. This is evident from the MPG Marathon where cars often beat their official figures on real roads.