The new MercedesMercedes-BenzGermany, 1924 > present197 models
9852 photos
33 videos
CLA 180 BlueEfficiency EditionMercedes-Benz CLA 180 Blu...Germany, 2013 > present5 photos
has taken the title as the most aerodynamic production car currently on sale with a drag coefficient of 0.22. That beats the PriusToyota Prius Gen.3Japan, 2010 > present52 versions
118 photos
2 videos
with a coefficient of 0.25 and BMW 320d EfficienctDynamics with a 0.26 rating.

The car achieves its low rating with a 2.21m² front area and aerodynamic refinements over the standard CLA like a revised front air dam, tighter seals around the headlights, radiator shutters and spoilers to guide air around the wheels. 

The aerodynamics and efficient engine give the car 47mpg US (56.5mpg UK or 5l/100km) fuel economy and 118g/km of CO2 emissions, an 8% fuel economy improvement over the standard CLA 180 The car is powered by a 1.6-liter four-cylinder petrol engine with 120hp and 147lb-ft of torque. 

Mercedes has some work ahead if it wants to keep the title of most aerodynamic car. The Volkswagen XL1Volkswagen XL1Germany, 2011 > 201119 photos
is slated to have a drag coefficient of 0.186. 

Source: Autocar