Emissions and consumption: these are the differences in the NEDC and WLTP homologation cycles

For several years now we have been hearing about the importance of car consumption and emission levels. After the well-known dieselgate, several changes had to be made to the way these are measured, since it was shown that the NEDC cycle, which was used until September 2018, was quite easy to cheat. And so, from 1 September, the new WLTP cycle came into force.

This may be somewhat confusing, but the authorities have worked to ensure that the data provided by the tests for the homologation of vehicles before they go on sale are as close to reality as possible. Although both systems serve the same purpose, measuring the emissions and consumption of cars, each system uses different methods. Let’s look at how they differ and why the WLTP cycle is more reliable.

WLTP cycle, more reliable and safe

To begin with, the acronym WLTP stands for World-wide harmonized Light duty Testing Procedure, or Worldwide Harmonised Light Vehicles Test Procedure. This system is similar to the previous one, the NEDC, but it is much more demanding and far exceeds its requirements.

The NEDC cycle carried out its tests in a closed space, on rollers. The test was a simulated route of about 11 kilometres, whereas the WLTP cycle increases this simulated distance to 23.25 kilometres, in a test lasting around 20 minutes.

The NEDC test temperature is around 20º, the ideal temperature for electric cars to function and which allows combustion-engine cars to perform at their best. The WLTP cycle, by contrast, runs the test at 14ºC, which is more detrimental to the operation of both types of vehicle.

You will have heard the old mantra of “city consumption, road consumption and combined consumption“. This has gone into history, since the WLTP cycle carries out four tests: maximum load, medium load, high load and very high load, which correspond to use in city, suburban, rural roads and motorway.

Another difference is that in the NEDC cycle cars were stationary for 25% of the time, whereas in the WLTP cycle this is reduced to 13%, which will prevent cars with a Stop&Start system from gaining an advantage in consumption and emissions. The speed and power used for the measurements are also higher now.

As regards speed, it has risen from 121 kilometres per hour to 131 km/h, and the working power has gone from 34 kW, the equivalent of 45.5 CV, to 47 kW, which equals 65 CV. The average power was 4 kW and now reaches up to 7 kW, that is, 5.3 CV and 9 CV respectively.

Equipment has become another indispensable element, since the WLTP cycle takes into account each equipment level, as it causes changes in the results obtained. And most importantly: the tests of the NEDC cycle were run on a test bench, but the WLTP cycle also includes specific tests in real driving modes, so the data are much closer to reality.