Types of E39 M5 Diffuser
The E39 BMW M5, produced from 1998 to 2003, is a high-performance sports sedan featuring distinctive front and rear bumper designs typical of high-performance vehicles. The E39 M5 diffuser serves as a key aerodynamic accessory that enhances both performance and aesthetic appeal.
E39 M5 Rear Diffuser
Located on the car's underbelly just ahead of the exhaust pipes, the rear diffuser is engineered to:
- Maximize performance by reducing aerodynamic drag
- Enhance the vehicle's visual appeal with a sportier, aggressive look
- Create significant downforce at high speeds
Design options: Fin count varies from three to five or more, with different shapes including curved and triangular designs.
Materials: Typically manufactured using plastic, carbon fiber, or fiberglass
E39 M5 Front Diffuser
Installed at the vehicle's front bumper and extending to the underbelly, the front diffuser:
- Improves aerodynamics for enhanced performance
- Reduces lift at high speeds, keeping the car firmly planted
- Complements the BMW E39 M5's overall aesthetic appeal
Design options: Various fin configurations and shapes to match the vehicle's styling
Materials: Available in ABS plastic, fiberglass, and premium carbon fiber
Expert Tip: When selecting between front and rear diffusers, consider their complementary aerodynamic effects. Installing both can provide the most balanced performance improvement, particularly for track use or high-speed driving.
Specifications and Maintenance of E39 M5 Diffuser
Design and Functionality
The E39 M5 diffuser balances functional aerodynamics with stylistic elements, focusing on reducing drag while creating a distinctive visual signature. Properly designed diffusers integrate seamlessly with the vehicle's existing body lines while providing measurable performance benefits.
Material Comparison
| Material | Weight | Durability | Appearance | Cost | Best For |
|---|---|---|---|---|---|
| Carbon Fiber | Very Light | Excellent | Premium, High-Tech | High | Performance enthusiasts, track use |
| ABS Plastic | Light | Good | Good with proper finish | Moderate | Daily drivers seeking performance gains |
| Fiberglass | Moderate | Good | Customizable | Moderate | Custom applications, flexible styling |
| Polypropylene | Light | Good | Practical | Low | Budget-conscious owners |
Design Features
Fins
Multiple fins of various sizes and shapes increase downforce and stability at high speeds, creating channels for airflow management.
Vents
Strategic venting improves airflow and enhances cooling performance for critical components like brakes and the differential.
Integrated Exhaust
Precision-designed cutouts accommodate factory or aftermarket exhaust systems while maintaining optimal aerodynamic properties.
Styling Elements
Aggressive styling enhances the vehicle's performance-oriented image while maintaining functional aerodynamic benefits.
Maintenance Guidelines
Regular Maintenance
- Clean thoroughly with mild soap and water to remove road debris
- Inspect for damage, cracks, or signs of stress
- Apply appropriate protective coatings for the specific material
- Check mounting hardware for tightness after highway driving
Performance Maintenance
- Verify secure attachment and proper alignment quarterly
- Check for vibration or unusual noises at high speeds
- Inspect underside for damage after encountering road debris
- Reapply UV protection to prevent material degradation
Maintenance Tip: For carbon fiber diffusers, avoid automatic car washes with brushes as they can create micro-scratches. Instead, hand wash with a microfiber cloth and pH-neutral soap, followed by a specialized carbon fiber sealant to maintain the glossy finish.
How to Choose E39 M5 Diffuser
Selecting the right E39 M5 diffuser requires careful consideration of several key factors to ensure optimal performance, fitment, and aesthetic appeal.
Key Selection Criteria
Material Considerations
Different materials offer varying benefits:
- Carbon Fiber: Lightweight, premium appearance, maximum performance
- Polyurethane: Flexible, affordable, corrosion-resistant
- Stainless Steel/Aluminum: Exceptional durability, heat resistance
Vehicle Compatibility
Ensure precise fitment:
- Verify compatibility with your specific E39 M5 model year
- Consider modifications to exhaust systems
- Check for proper clearance with other aftermarket components
Design and Aesthetics
Select a style that complements your vision:
- Choose between aggressive racing-inspired designs or subtle enhancements
- Consider fin configuration (quad vs. curved designs)
- Ensure visual harmony with other exterior modifications
Performance Goals
Align with your driving objectives:
- Track-focused designs offer maximum downforce
- Street-oriented options balance looks and functionality
- Consider the aerodynamic package as a whole
Selection Tip: When upgrading to a performance diffuser, consider the complete aerodynamic balance of your vehicle. Adding a rear diffuser without appropriate front aerodynamics can create imbalanced downforce distribution that may affect high-speed handling.
How to DIY and Replace E39 M5 Diffuser
With the right tools and preparation, replacing your E39 M5 diffuser can be an achievable DIY project that enhances both performance and aesthetics.
Gather Tools and Materials
Collect all necessary equipment before beginning:
- Screwdriver set (Phillips and flathead)
- Trim removal tool
- Impact wrench or socket set
- Jack and jack stands rated for your vehicle's weight
- New E39 M5 diffuser kit with hardware
- Work gloves and safety glasses
Prepare the Vehicle
Safely elevate your M5 for access:
- Park on a level surface and engage the parking brake
- Place wheel chocks against the front tires
- Carefully jack up the rear of the vehicle
- Secure with properly positioned jack stands
Remove the Original Diffuser
Carefully detach the existing component:
- Locate and remove all mounting screws at the bottom and sides
- Use trim removal tools to carefully release retaining clips
- Support the diffuser while removing final attachments
- Gently pull the diffuser away from the bumper
Prepare the New Diffuser
Before installation:
- Inspect the new diffuser for any shipping damage
- Test-fit without fully attaching to verify alignment
- Prepare any included mounting hardware
Install the New Diffuser
Secure the new component:
- Align the diffuser precisely with the rear bumper
- Begin by engaging center attachment points
- Work outward, securing clips and fasteners
- Verify even gaps and proper alignment
Secure All Mounting Points
Ensure proper attachment:
- Install and tighten all screws to manufacturer specifications
- Verify all clips are fully engaged
- Check for any loose areas or misalignment
Final Inspection and Test
Verify successful installation:
- Lower the vehicle carefully from jack stands
- Inspect from all angles for proper fitment
- Start the engine and check for unusual vibrations
- Take a test drive, listening for any rattles or noises
Installation Tip: Take photos of the original diffuser's mounting points and hardware placement before removal. This documentation can be invaluable reference during installation of the new component, especially for complex mounting arrangements.
Frequently Asked Questions
The E39 M5 rear diffuser installation process requires careful preparation and attention to detail:
- Thoroughly clean the mounting area to ensure proper adhesion
- Carefully align the diffuser with the rear section of the vehicle
- Mark drilling locations for aftermarket diffusers requiring new mounting points
- Apply automotive-grade double-sided tape for adhesive-mount diffusers
- Secure with appropriate bolts, screws, or clips based on manufacturer specifications
- Verify proper alignment and make any necessary adjustments
- Conduct a test drive to check for vibrations or unusual noises
Professional installation is recommended for carbon fiber diffusers to prevent damage to the premium material during the mounting process.
No, the E39 M5 diffuser is specifically engineered for the BMW E39 5 Series M5 models (1998-2003). The unique dimensions and rear bumper design of the E39 M5 mean these diffusers are not directly compatible with other BMW models.
While some aftermarket manufacturers produce adaptable diffusers that can fit multiple BMW platforms, these typically require modifications and may not provide the optimal aerodynamic benefits of a model-specific design. Always verify compatibility with your specific BMW model year and variant before purchasing.
For other BMW models, it's advisable to seek diffusers specifically designed for that particular chassis code and generation.
While the E39 M5 diffuser doesn't significantly impact regular vehicle maintenance, it does introduce several considerations:
- Cleaning Requirements: The diffuser creates additional surfaces that collect road debris, salt, and grime, requiring regular cleaning to maintain appearance and prevent corrosion of mounting hardware
- Inspection Points: The diffuser and its mounting points should be checked during routine maintenance for secure attachment
- Ground Clearance: Aftermarket diffusers may reduce ground clearance, requiring additional caution when driving over speed bumps or entering steep driveways
- Service Access: Some diffuser designs may need to be partially removed to access certain undercarriage components during service
Regular inspection of the diffuser mounting points is recommended, particularly after high-speed driving or encountering road debris, to ensure continued secure attachment and optimal performance.
E39 M5 diffusers are manufactured using several materials, each with distinct characteristics:
- Carbon Fiber: Premium option offering the best strength-to-weight ratio. These diffusers provide maximum performance benefits while reducing unsprung weight. The distinctive weave pattern also delivers a high-end aesthetic appeal. However, they command the highest price point.
- ABS Plastic: This durable thermoplastic offers good impact resistance and UV stability. ABS diffusers provide a balance of performance, durability, and affordability, making them popular for daily-driven vehicles.
- Fiberglass: Offering excellent formability and moderate weight, fiberglass diffusers can be crafted into complex shapes. They're more durable than plastic but more affordable than carbon fiber, positioning them as a mid-range option.
- Polyurethane: Known for flexibility and resistance to impacts, polyurethane diffusers are ideal for street-driven cars that might encounter speed bumps or driveway inclines.
Material selection should be based on your specific driving conditions, performance goals, and budget constraints.