Well, here goes the reputation of the German car makers, or at least the one of Volkswagen – does it? Cheating is not too special in many areas, but of course none of the instances involved wants to be busted. Volkswagen got busted now and as a first consequence Martin Winterkorn left.
What makes one wonder is that Volkswagen does not really have that competitive edge we would expect from a good cheater – at least Lance Armstrong had one.
As we learned from professional cycling, (almost) everyone did dope but only (too) few actually were convicted. Thus the question arises, whether Volkswagen is the black sheep, or the industry as a whole is cheating? So what is actually behind the #dieselgate or #vwgate?
I did collect some data from the manufacturers websites regarding fuel consumption, and compared it to what actual users report on Spritmonitor.de. The data collection (if existing, I used the smallest Diesel engine for each car size class) looked to be easy at first sight, but is a bit tricky regarding sample sizes and comparability – but it does not look too bad.
Lets first look at how much percent cars did consume more than advertised (let’s call this variable excess for now):
With just 14% it is actually Volkswagen’s Pheaton – a well known gas guzzler, which is actually rated as one, even by VW. Top scorer, with 73%, is Audi’s Q7.
Let’s now look at boxplots of excess by make
and car size
As the engines of VW and Audi are largely the same, it is quite surprising that VW is closest to what they advertise while Audi seems to be far off. Probably an indication that the typical drivers of a manufacturer have a big impact as well.
Less surprising is that larger cars are the worst cheaters, as this can be explained by simple physics.
Let me conclude with the scatterplot of all data
The diagonal is what we as consumer should get, but all car makers seem to cheat equally well – so let’s see who is next to get busted?!
PS: Fuel consumption is here used as a proxy of overall emissions, which are hard to measure otherwise.