Official emissions tests due to be launched in 2017 are inaccurate and will penalise cars with small, fuel-efficient engines, experts claim.
The new tests are designed to answer criticism of the current assessment programme, the New European Driving Cycle, which on average shows cars are 30% more fuel efficient than their real-world performance.
A new assessment programme, the World Light Vehicle Test Procedure (WLTP), is designed to resolve the problem. However, it is feared it will still overstate fuel economy by 15% and provide an inaccurate picture of total cost of ownership.
Engine expert Stefan Carstens says changes to the system improve the official fuel economy of larger-engined cars, because the new test accelerates vehicles faster and to higher speeds. The test puts greater load on smaller engines, which harms their fuel economy.
He told Der Spiegel: ‘Depending on the engine, the effect is very different. Consumption figures for cars with small engines will deteriorate.’
His views were supported by Nick Molden, founder of real-world driving data company Emissions Analytics.
He said: ‘The conditions of the WLTP are better for larger-engined cars, which may return higher fuel economy than under the current test.
‘Smaller engines will be under greater load, so their economy may decline. There will be a greater advantage if they have hybrid technology.’
Molden argues the tests will still provide an inaccurate picture of fuel economy. However, the margin of error will be reduced because the WLTP closes some loopholes that manufacturers could previously use to enhance a vehicle’s efficiency during testing.
He said: ‘It reduces the level of optimising vehicles for tests and legal gaming of the system. However, there will still be a 15% difference in fuel economy between the test and real-world driving.’
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