The official CO2 emissions figure of the new Volkswagen Up GTI has been raised from 110g/km to 127-129g/km after testing on the new Worldwide Harmonised Light Vehicles Test Procedure (WLTP).
The first Volkswagen model to be tested in this new format, which replaces the New European Driving Cycle (NEDC), has also had its quoted combined economy reduced from 49mpg to 42mpg as a result.
Both changes equate to about 15% reductions in efficiency, revealing the impact the new, more stringent real-world tests can have compared with the lab-based NEDC test, which had not been revised since 1997.
The WLTP regime includes higher driving speeds than NEDC and harder acceleration and deceleration. It also tests cars with and without optional equipment to offer a best and worst-case scenario, hence the CO2 range published for the Up GTI.
Both NEDC and WLTP figures will continue to be produced until September 2018, after which only WLTP figures will be shown to customers.