A rear diffuser is a fantastic upgrade for the rear end of your BMW F30. M Performance style rear bumper diffusers can enhance the look of the 335i and 340i with the M-Sport rear bumper and give the car a refreshed and more aggressive appearance.
Unlike the factory diffuser, upgraded diffusers have fins at the bottom, making your F30 stand out and giving it a slight aerodynamic edge at high speeds. That said, an aftermarket rear diffuser is a purely cosmetic upgrade, with no noticeable effect on performance.
Here are some of the best rear diffuser options for the F30 335i and 340i:
Rear Diffusers for BMW F30 335i & 340i
1. Ikon Motorsports M Performance Rear Diffuser
Quick Overview
- Fits BMW F30 335i & BMW F30 340i with the M-sport package
- The matte black color can be painted or wrapped to match the body color of your BMW
- Accentuates the sporty appearance of your vehicle.
- Made with high-quality Polypropylene material.
The Ikon Motorsports diffuser is made for dual exhaust opening F30 such as the 335i and 340i. It doesn’t look like much at first glance – it’s pretty discreet. But it’s still eye-catching enough to bring out that sporty vibe in your F30. It has three fins at the center, giving your vehicle a nicely aggressive profile when looked at from behind. The fins further add to the diffuser’s aerodynamics.
This rear diffuser comes unpainted with a matte black finish. You can either use it as is with its matte paint, wrap it in carbon fiber or take it to your local body shop to get it prayed. We recommend a wrap as it is easily removable, and you can change between matte black and other colors if desired.
Compatibility:
- 2012-2015 BMW F30 335i with M-Sport rear bumper
- 2016-2018 BMW F30 340i with M-Sport rear bumper
2. Rear Bumper Diffuser for BMW F30 335i 340i
Quick Overview
- Fits BMW 335i & BMW 340i models with the M-sport package
- Carbon fiber material with glossy clear coating for the ultimate sporty look
- Lightweight & top grade carbon fiber ensure long durability and weight savings
If you’re looking for a carbon fiber rear diffuser, this item is made with high-grade carbon fiber and a glossy clear finish. It’s lightweight, durable, and significantly improves your car’s down-force. This model is a fantastic fit for BMW F30s with dual exhausts such as the 335i and 340i. It works with F31 models as well.
The rear diffuser has uniquely thick fins and boasts the traditional weaved carbon fiber look that any sports car enthusiast would enjoy in an aftermarket accessory. To complete a full carbon fiber look on the car’s rear, you could also opt for a carbon fiber spoiler. A trunk-mounted lip spoiler would complement the diffuser for a truly aggressive look.
Compatibility:
- 2012-2015 BMW F30 335i with M-Sport rear bumper
- 2016-2018 BMW F30 340i with M-Sport rear bumper
3. Carbon Fiber Rear Diffuser for BMW 3 Series F30 2012-2018
Quick Overview
- Fits BMW 335i & BMW 340i models with the M-sport package
- Glossy black matches well almost every color
This is another carbon fiber rear diffuser alternative for the BMW F30, made with a real carbon fiber structure for true light savings and rigidity. This accessory also features a delicate weaving texture with an elegant gloss finish that can withstand extended exposure to the elements and heat coming from the exhaust tips.
Thanks to its UV-protective clear coat, it is both fade- and dust-resistant, so you don’t have to worry about wear and tear. This diffuser includes installation hardware such as the required self-tapping screws.
Compatibility:
- 2012-2015 BMW F30 335i with M-Sport rear bumper
- 2016-2018 BMW F30 340i with M-Sport rear bumper
4. BMW 3 Series 335i 340i Quad Exhaust M Performance Rear Diffuser
Quick Overview
- Fits BMW 335i & BMW 340i M-sport package and quad aftermarket exhaust
- Excellent if you ever plan to upgrade to an M-like exhaust
- Glossy carbon fiber offers weight savings with a durable finish
- Includes self-tapping screws for simple installation
If you have a modified F30 335i or 340i with an aftermarket quad exhaust, a regular rear diffuser won’t fit your vehicle as the extra exhaust tips will need additional space.
The M Performance rear diffuser has an extra wide exhaust outlet gap, to accommodate the quad exhaust system. In addition to the already aggressive-looking rear when equipped with an aftermarket exhaust system, the carbon fiber diffuser will have your BMW F30 looking almost like a true M-car.
It is made out of resilient FRP material, which makes it super-durable and extremely lightweight. This diffuser is resistant to fading thanks to the UV-protective clear coating. Overall, it will emphasize the sporty appearance of your F30.
Compatibility:
- 2012-2015 BMW F30 335i with M-Sport rear bumper and quad exhaust setup
- 2016-2018 BMW F30 340i with M-Sport rear bumper and quad exhaust setup
Compatibility
Unlike most aftermarket upgrades, rear diffusers are tailor-made for specific car models. The four diffusers outlined above are all F30-specific and particularly aimed at BMW F30/F31 3 Series 335i and F30/F31 340i of the years 2012-2018.
Even more specifically, these diffusers will only fit M-Sport bumpers. If your vehicle has a standard bumper, you must replace it with the M-Sport bumper to install the rear diffusers.
BMW F30/F31 Rear Diffuser Installation Process
Most vehicle aftermarket upgrades are relatively straightforward, although it’s always recommended that you take your BMW to an auto shop and let body technicians take care of it to reduce the chances of damage.
Here’s how to install a rear diffuser on your BMW F30 3 Series:
1. Remove bolts of factory diffuser
To swap out the original diffuser on your F30 BMW, you need to remove the 8mm bolts found underneath the diffuser – there are five bolts, two on each side and one at the center of the diffuser. This, however, won’t completely loosen the old diffuser. There are clips on the top that keep the diffuser in place.
2. Remove the factory diffuser
Before moving on to removing the diffuser by unhooking the clips, make sure that your exhaust isn’t hot to avoid burns. Start popping the clips out by pulling their upper side.
3. Install the new aftermarket diffuser
Take the new diffuser and put it over the exhaust tips. There is a piece that you need to place in position accurately to make sure the diffuser is over the center part of the lower side of your bumper. Starting at the center, push the diffuser until you hear a click, indicating that its central part has attached to the clip.
Then, work your way to either side until you’ve hooked it onto each clip. Repeat this on the other side. Every single clip must be in place before moving on to putting the screws back in place.
Note: Removing the reflectors isn’t necessary, but it may make it easier for you to put on the new diffuser. Access the reflector clips from the clip-side of the diffusers and gently push them out. Put them back in by simply pushing them into place from the outside part of your vehicle.
4. Secure and re-install bolts
It’s essential that the diffuser is completely in place before putting the screws back in place. Make sure that every clip is in place. Then, put the screws back into their original positions. They need to be firmly in place.
Frequently Asked Questions
How does a rear diffuser work?
As you drive your car at moderate speeds, some air passes underneath the vehicle. As you drive faster, the pressure increases. However, the full potential of this pressure isn’t utilized. With advanced factory diffusers, the air expands as it goes through the expansion chamber. This decreases the pressure underneath the vehicle.
So, now you have high-pressure air moving above the vehicle, while the diffuser is sucking out the air from underneath the car, which creates a vacuum. This increases the down-force of your vehicle.
In other words, your vehicle is sucked downward, while the aerodynamic drag is reduced. This means a better grip on the road, further enhancing your vehicle’s handling and stability at moderate to high speeds.
Can diffusers improve grip and handling on the street?
It’s very important to note that down-force starts impacting your car’s performance only at high speeds. At low speeds, the pressure reduction created by rear diffusers is insignificant and minuscule. So, don’t expect any increased grip or handling at low-to-mid speeds. Only at moderately high speeds, you’re bound to feel the difference that rear diffusers bring to the table.
Are aftermarket diffusers functional or just for looks?
Aftermarket diffusers are aesthetic modifications with no or minimal effect on performance.
There are three critical components of highly-effective, factory-made diffusers: vertical fins, smooth underbody, and the expansion chamber. The above aftermarket rear diffusers don’t have expansion chambers. However, they all have vertical fins, as well as a smooth underbody.
Conclusion and recommendation
Rear diffusers are an excellent modification to your M Sport BMW F30 and enhance rear looks significantly. The above carbon fiber diffusers won’t provide a significant aerodynamic performance enhancement, but they are simple to install and a cost-effective mod.
We recommend the Ikon Motorsports M Performance Style diffuser, as you can wrap it in the color of your vehicle and then install it for an excellent fit.
Have any rear diffuser recommendations? Please let us know. Happy modding!