Audi B9 A4 S4 MD Style Carbon Fiber Rear Lip Diffuser 2017-2018

Enhance the rear styling and aerodynamic performance of your 2017-2018 Audi B9 A4 Sport or S4 with this MD Style carbon fiber rear lip diffuser. Designed to deliver a more aggressive and performance-inspired rear profile, this diffuser adds depth and definition to the lower bumper while maintaining a clean OEM+ appearance.

Precision-engineered for the Audi B9 platform, this rear diffuser is designed as a direct replacement component, utilizing the original mounting points for a seamless and secure fit. The MD styling improves rear-end presence and complements the sporty design of the A4 and S4 models.

Constructed from high-quality carbon fiber, this rear diffuser offers lightweight durability, structural strength, and a premium finish. Available in multiple carbon fiber options, it is ideal for daily driving, performance builds, and show-quality vehicles seeking an upgraded exterior appearance.

Product Specifications

Key Features

• Designed for 2017-2018 Audi B9 A4 Sport and S4 models
• MD Style rear diffuser for enhanced sporty rear-end styling
• Direct replacement design utilizing original mounting points
• Carbon fiber construction for lightweight durability and strength
• Available in CFRP and forged carbon fiber finishes
• Precision fitment aligned with factory rear bumper mounting points
• Enhances rear aerodynamics and airflow management
• Improves lower bumper definition and aggressive styling
• Maintains OEM+ fit and clean body line integration
• Suitable for daily driving, performance builds, and show vehicles

Configuration Options

• CFRP – Traditional carbon fiber weave with a glossy finish
• Forged Carbon Fiber (FGCF) – Distinct marbled carbon pattern for a modern performance look

Package Includes

• Rear lip diffuser

Note: Products marked as PRE-ORDER require production prior to shipping. Air shipping ETA is approximately 5–6 weeks, while container shipping ETA is approximately 3–4 months. Delivery times may vary depending on production schedules.

Installation

• Direct replacement installation
• Uses original factory screw holes
• No drilling required
• No permanent modification required
• Professional installation recommended

Fitment

• 2017-2018 Audi A4 B9 Sport
• 2017-2018 Audi S4 B9

United States: Free shipping available to the lower 48 states across all items. Other states will incur a shipping charge.

Worldwide: Free shipping is available for Complete Headlights, Taillights, DRLs. For custom headlight retrofits, carbon fiber products, and performance products, there will be a shipping charge.  

Please note:
• For Retrofits, you are purchasing a headlight modification service.
• If you select "Shipping own headlights to BayOptiks for modification", you are required to send us your headlights.
• If you choose "Purchase new OEM headlights", we will order and modify a new OEM headlight for you.
• Once your customizations are complete, we will ship it to you!

• Complete Headlights: 3-5 business days for order processing plus shipping time.
• Custom & Pre-Built Headlights: 6-8 weeks depending on the complexity and component availability.
• New OEM and cores: 6-8 weeks plus an additional 4-8 weeks as these are special orders base on the vehicle VIN due to different versions (North American, European, etc.)
• DRLs, Taillights, Brake Pads, and Carbon Fiber Aero: 3-5 business days for order processing, plus shipping time.
• Lens Replacements: 1-3 weeks plus shipping time.

Please note, we do not have control over the time frames of our vendors, manufacturers, and delivery services as they may delay processes in regards to components and shipment.