An aerodynamic diffuser, rear diffuser or automotive diffuser is a feature used on the underside of a vehicle to
improve the aerodynamic properties of the vehicle.
An aerodynamic diffuser causes the air under the vehicle to move faster than the air around other areas of the
vehicle. This creates a low pressure under the vehicle and this low pressure causes the bottom of the vehicle to be vacuum
sucked to the ground thereby increasing the downforce of that vehicle.
The rear diffuser allows the air under the vehicle to exit from under the vehicle easily and occupy the low pressure
area that is created behind the vehicle as it moves.
Common designs for aerodynamic diffusers on passenger and other street legal vehicles:
The diffusers can be made from a number of materials such as plastic, aluminium or
carbon fiber and they are usually black or a dark colour so an aerodynamic diffuser would easily stand out and be
noticable at the rear of your car, less so if your car is black.
- It is always on the lower part of the rear bumper as it starts from under the vehicle and ends on the rear bumper.
- They are usually wide enough to cover two thirds to three quarters the width of the rear bumper and by extension the
width of the vehicle.
- The rearmost part of the diffuser is always higher than the front of the diffuser which is under the car. Aerodynamic
diffusers can be from less than one foot to up to four feet extended under the car in different vehicles for varying
- There are several vertical fins pointing downwards, the number of fins can vary again from two to eight on different
vehicles for varying effectiveness.
Some vehicles would have a rear diffuser along with the aerodynamic benefits incorporated into the vehicle design
from inception but some aerodynamic diffusers can be bought and installed as an aftermarket part.