Where to start?
Current vehicles are tested under the New European Driving Cycle (NEDC).
From 2019 the EC moves across to the World Light Vehicle Test protocol (WLTP).
WLTP is massively complex. In theory, it is supposed to represent a driving cycle that is more reprentative of 'normal' driving. In reality, the test scheme is not perfectly clear. We don't know how certain very detailed aspects of the WLTP will work out. Such as, for example, different size of exhaust pipe, or different wheel designs, or different tyre suppliers.
Each individual variant of a vehicle will have its own rating under WLTP. So not just the sport variant, but the sport variant with sporty wheels and the sport variant with sporty wheels and Pirelli tyres will have a different raring from the sport variant with sporty wheels and Michelin tyres.
Within the industry, it is a huge deal.
For consumers, a bit less so.
Except that initial purchase price and ongoing taxation rates will be affected by the WLTP rating.
Massively complex change, but exciting, if you are in the business....
Essentially it drives vehicle makers to be as energy-efficient as possible