CLA 45 AMG is a special version of the brand famous sport coupe that is upgraded with AMG aerodynamic package.

Length4694 mm
Width1999 mm
Height1408 mm
Wheel base2728 mm


The diffuser on CLA 45 AMG does help increasing the air flow underneath the car which can reduce air pressure and thus increase the downforce. Detail will be discussed in the pressure and velocity plot sections.


Front wings

Two small wings are placed in front of each front wheel that can generate significant amount of downforce on the front axle. The pressure plot will illustrate how these wings work.

Simulation model

A full scale model was put into virtual wind tunnel for testing. Wind speed is 27.7 m/s and with moving floor.

ResultsValueCoef.Official Coef.
Drag134 N0.3190.31
Lift26 N0.062
Pitching (-ve down)-180 Nm-0.176
Force results from simulation (Wind speed 27.7 m/s)

Drag and lift

The CLA C45 AMG has a similar level of drag force as the BMW X1 which is quite high for a coupe. This high drag can be explained when comparing pressure distribution plot between Tesla Model S and CLA 45.

There is a large a region of high pressure (Red) at the front mask air intakes for the 375hp engine cooling. The slope of the rear glass has a much steeper angle than the Model S that makes the air pressure harder to recover to atmospheric pressure and thus create drag

This car generates slight amount of lift in total. However the large negative pitching moment value shows that a large high downforce act on the front axle. This mainly comes from the air splitter at the front bumper where high pressure on the top surface and low pressure at the bottom surface to generate downward force. Moreover the two small wing on the side of the bumper also contribute to a small portion of the downforce.

From the centre plane velocity plot below, we can see airflow from the bottom following closely to the rear diffuser to join the rear wake and reduces the low pressure zone and thus reduces drag.


Total pressure isosurface illustrate that the major pressure loss is due to the rear part of the car where a huge loss zone exist behind the rear wheel. The shape of the isosurface is a lot clumsy than the Model S.


The AMG package produces large downforce on the front axle which may reduce the understeer behavior during cornering while reducing drag may not be the main focus because of its powerful engine. However it is worth mention that there is room for drag reduction by changing the shape of rear body.