How a Rear-End Diffuser Benefits Your BMW

How a Rear-End Diffuser Benefits Your BMW

The BMW is known for its sophisticated style and classic lines. For decades, BMW loyalists have driven this beautiful machine for the sole purpose of driving a status symbol, and also because it is built to run well and last forever. Although it’s tough to improve an already luxurious car, auto body kits offer aerodynamic additions designed for such purposes. In this article, we will discuss how a rear-end diffuser benefits your BMW.

What Is a Rear-End Diffuser?

A rear-end diffuser is a modification added to a car to increase aerodynamics by increasing the downforce and decreasing drag.

It does so by grabbing the air that flows under the car while driving and passing it through the diffuser’s expansion chamber, creating a reduced air speed (high pressure to low pressure,) and thus generating a greater downforce.

Imagine a vacuum of sorts sucking the air out from underneath the car, reducing pressure underneath, and raising it above. Downforce is the combination of airflow and gravity, holding the car to the ground. Increased downforce means a stronger grip to the ground. In other words, greater handling and better aerodynamics.

The rear-end diffuser is also designed for the creation of a new exhaust configuration, such as dual exit, rather than the stock single exit exhaust.

The use of a diffuser is typically seen in race cars, but we are seeing more and more racing elements make their way to everyday cars, thanks to a desire for better aerodynamics.

Where Is a Rear-End Diffuser Located?

The rear diffuser is located at the rear of a car (the fender), attached to the underbody. Most often, diffusers are sold as an aftermarket modification or upgrade. However, BMW offers the rear diffuser as a factory install on many of its models.

Main Components of the Rear-End Diffuser

There are two important parts to the rear-end diffuser:

  1. The vertical fins give the air a safe path to exit from underneath the car. Without the vertical fins, the air wouldn’t be controlled and could cause dangerous turbulence.
  2. The expansion chamber is where the air is changed from high to low pressure, leading to the added downforce for improved aerodynamics.

Another important element to the rear diffuser, although not an actual part of it, is a smooth underbody on the car. Basically, the smoother the underbelly, the slicker the surface is for air to escape through the diffuser. The smoothness gives less possibility for air to get stuck anywhere.

Installing a Rear-End Diffuser

To install a rear-end diffuser, holes are drilled into the fender and the rear tire wells. The diffuser is then attached using brackets, which are first installed onto the diffuser itself.

It sounds simple enough, but with all of the little things that could go wrong—such as the car getting scratched or something not lining up correctly—it’s highly recommended that a professional installer be used to install body parts like a rear-end diffuser.

Materials Used for a Rear-End Diffuser

Material matters and there are several options for creating a rear diffuser. They are as follows:

ABS Plastic

Created using three compounds, ABS plastic is a strong and resilient thermoplastic and an excellent option for a rear diffuser. It’s resistant to heat and easy to paint, making it a favorite of BMW and all car modifiers.


Fiberglass has long been used in car modifications because it’s lightweight and also easy to paint. The rigidity of fiberglass makes it heat-resistant, but unfortunately also makes it easy to crack when working with it.


Resistant to cracking and highly flexible, polyurethane is nice to work with when making car modifications.

It’s tough to get paint to adhere to polyurethane’s slick surface, and racecar drivers don’t want it anywhere near their cars because of its weight.

Carbon Fiber

Strong yet lightweight, carbon fiber is considered the best of the best by many car enthusiasts.

Epoxy is mixed with carbon fibers, creating a strong and durable material. Thanks to its superior strength while remaining lightweight, racecar drivers trust carbon fiber even more than steel—your BMW will too.


The best of both worlds, composite materials are created using a mix of two or more materials to create a lightweight, strong, and flexible option.

As you can see there are many options for materials when designing a rear-end diffuser. When choosing a rear-end diffuser for your BMW, make sure to speak with a body kit manufacturer who specializes in luxury vehicles such as BMW.

Can a Rear-End Diffuser Be Removed?

Yes, a rear-end diffuser can easily be removed by removing the bolts. However, because accidental damage can easily happen, please allow a professional to uninstall your rear diffuser.

Does a Rear-End Diffuser Add Value?

The answer to this question is both yes and no. It really depends on who’s purchasing the car.

Gearheads who appreciate what a modification does for a car will no doubt notice the rear-end diffuser and see it as a bonus, and will possibly even be willing to pay more than what they would for a BMW or other luxury car without one. In that case, the rear diffuser does add value.

A novice or someone simply looking for a great car may not understand your enthusiasm for the addition of a diffuser. You’ll likely scratch your head in confusion as they tell you they’ve never heard of a rear diffuser, and we are right there with you. Still, not everyone wants a modification. Ultimately, sources such as Kelley Blue Book don’t recognize aftermarket parts as additional value.

In conclusion, a rear-end diffuser benefits your BMW with improved aerodynamics for a smoother ride, and it additionally creates a sporty look of the car’s rear end. Not all BMW models come from the factory with a rear-end diffuser, but many do, such as the M3/M4 CS, F90 M5, and M4 GTS.

DarwinPro Aerodynamics offers the BMW body kit for sale, along with all luxury car body kit needs. We share the same passion for all things supercar, just like you do. Contact us, and let’s see how we can take your car from great to luxurious.

How a Rear-End Diffuser Benefits Your BMW

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