Precision Fitment
Each part is 3D-scanned against the platform and digitally modelled before tooling — so fitment is engineered, not approximated.
Audi A4 B9 S-Line / S4 Carbon Fibre Rear Diffuser with 3rd Brake Light
£559.00
ASM Sports Tech offers a precision-crafted diffuser tailored to fit the Audi A4 / S4 B9.
Specialist online — replies in minutes
Speak to ASM before you order
Straight answers on fitment, lead time and build direction — direct from the team that engineers it.
Open WhatsApp LineDoubt removed
before commitment
Every component leaves on one standard: measured fitment, disciplined materials, and a specialist on the line before and after you order. The proof sits below — not the promise.
Composite Construction
Pre-preg carbon and lightweight composite, finished to a consistent standard and built for structural intent — not cosmetic weight.
Support, Both Sides of the Sale
A specialist answers fitment, lead time and compatibility before you order — and stays reachable after it ships.
Audi A4 B9 S-Line / S4 Carbon Rear Diffuser with Led
Give your Audi A4 B9 S-Line or S4 a dynamic, performance-driven upgrade with the ASM Sports Tech Carbon Fibre Rear Diffuser with Integrated 3rd Brake Light — designed to enhance aerodynamics and rear-end style with OEM precision.
Constructed from authentic carbon fibre, this diffuser combines ultra-lightweight strength with a flawless gloss finish. The integrated LED 3rd brake light adds a distinctive motorsport touch while improving visibility and safety. The aggressive fin layout optimizes airflow under the rear bumper, reducing drag and improving stability at speed.
Compatible Models:
- Audi A4 S Line (B9) 4-Door Saloon (2016 – 2019)
- Audi S4 (B9) 4-Door Saloon (2017 – 2019)
Features & Details
Premium Carbon Fibre Material
Enhance your Audi’s rear end with a lightweight, sturdy, and stylish carbon fibre diffuser that ensures longevity and a sleek appearance.
Aerodynamic Design
This diffuser is engineered to streamline airflow, improving fuel efficiency and reducing drag for an enhanced driving experience.
Integrated Rear Brake LED Light
The built-in LED light increases visibility, adding an extra layer of safety and a modern touch to your vehicle.
Easy Installation
Designed for a seamless fit on Audi A4 B9 S-Line and S4 B9 models, ensuring hassle-free installation.
Stylish Upgrade
Elevate your vehicle’s look with this aggressive yet elegant rear design, a must-have for any Audi enthusiasts.
Upgrade your Audi A4 B9 S-Line or S4 with the ASM Sports Tech Carbon Fibre Rear Diffuser with 3rd Brake Light, delivering a refined OEM+ aesthetic and genuine aerodynamic performance.
The questions
worth asking first
Fitment, installation, materials, lead time and support — the answers that settle the last doubts before you order. Anything not covered, the specialist line is one tap away.
Fitment is defined by the product title, the listed application scope and your platform. If you're unsure, open the WhatsApp line and a specialist will confirm the correct application before you order.
Yes — particularly for carbon aero, exhaust components and platform-specific upgrades, where alignment, finish protection and correct hardware positioning matter to the result.
It depends on the part, but the standard is consistent: disciplined finish, clean visual consistency and resolved platform-specific presentation. Pre-preg carbon and lightweight composite where the application calls for it.
It depends on whether the part is in stock or built to order. The estimated timeline on the product page is the reference to use before checkout — and the specialist line can confirm it for your exact spec.
Yes. For fitment, visual direction, material choice or build planning, use the WhatsApp block on this page and a specialist will guide you before you place the order.
Yes — worldwide shipping is available across most ASM Sports Tech lines. Method and transit time vary by product category, destination and dispatch origin.
Two ways
to order
Order directly with ASM Sports Tech, or through an authorised partner in your region. Same components, same standard — whichever route fits the build.
Regional Access
Prefer a local point of contact? An authorised ASM partner in your region can handle the order end to end.
Project-Based Ordering
Multi-part builds and full upgrade directions are best coordinated as one order — we'll plan it with you before placement.
Direct or Dealer
Order direct from ASM or through a partner — the parts, the fitment standard and the support are identical either way.
// ASM Sports Tech — The Programme
Complete the build
Matching components for the same platform — selected to fit alongside what you're ordering and finish the build as one resolved direction.
