2014-2020 BMW i8 Coupe Quarter Moulding: Decoding the Flying Buttress Trim
This guide covers the iconic exterior C-pillar 'flying buttress' trim, a key design element of the i8 Coupe that is prone to cosmetic damage and requires careful handling during replacement.
- This part is the exterior 'flying buttress' C-pillar trim, exclusive to the i8 Coupe; it does NOT fit the Roadster.
- Failure is typically cosmetic (scratches) or due to impact (cracks). There are no common mechanical failures or recalls for this specific part.
- When buying used, the most critical inspection is for intact mounting tabs and clips on the back of the panel.
- Replacement is a complex, high-risk job best left to a professional body shop due to hidden clips and the fragile carbon fiber body underneath.
Symptoms of a Failing or Damaged Quarter Moulding
Failure of the i8's quarter moulding is almost always cosmetic or the result of physical damage, rather than mechanical failure. Given its prominent location on the car's side profile, it is highly susceptible to damage.
- Cosmetic Blemishes: As a high-gloss black painted part, the moulding is prone to showing swirl marks, light scratches from washing, and hazing from sun exposure. Deeper scratches and rock chips are also very common, particularly on cars that are driven frequently.
- Cracks or Fractures: In the event of a sideswipe or impact, the composite material can crack or shatter. Stress fractures may also appear around the mounting points if the part was installed incorrectly or subjected to a minor impact.
- Loose Fitment or Rattling: The moulding is held in place by a series of clips, retainers, and brackets. Over time, or due to improper removal and reinstallation, these clips can break or lose their tension. This can cause the moulding to feel loose, vibrate at speed, or create a rattling noise. This type of failure is common on trim pieces for other BMW models and is a plausible issue for the i8.
Pro Tip: A related, well-documented issue on the BMW i8 is the tendency for the lightweight windshield to crack spontaneously. While this doesn't affect the quarter moulding directly, it highlights the unique properties and potential sensitivities of the advanced, weight-saving materials used across the vehicle. Buyers should be aware that components on the i8 may not have the same durability as on a conventional vehicle.
Buying a Used 2014-2020 BMW i8 Quarter Moulding
A used OEM quarter moulding is an excellent way to save money over a new part, especially for a vehicle like the i8 where new parts can be costly. However, careful inspection is critical before buying.
Key Inspection Points for a Used Moulding:
- Check for Cracks: Thoroughly inspect the entire surface for any cracks, especially around the edges and mounting holes. Pay close attention to the thin, floating sections of the design. Place the part on a flat surface to see if it sits true, which can reveal stress fractures.
- Inspect All Mounting Points: This is the most critical check. Flip the panel over and carefully examine every mounting tab, clip receiver, and bracket location. Compare it to photos of a new part if possible. Even one broken tab can cause the panel to fit loosely or rattle, and repairing them is often impossible.
- Evaluate the Surface Finish: Look for deep scratches, scuffs, or gouges. While light swirls can be polished out by a professional detailer, deep scratches in the plastic cannot be easily repaired. Refinishing high-gloss black plastic is challenging and may not perfectly match the other side of the vehicle.
- Verify the Part Number: Ensure the part number matches the side you need. The left (driver) and right (passenger) side mouldings are not interchangeable.
Compatibility Warning: This quarter moulding fits the 2014-2020 BMW i8 Coupe ONLY. It will NOT fit the i8 Roadster (convertible) model. The Roadster has a completely different rear body structure to accommodate the folding roof and lacks the Coupe's 'flying buttress' C-pillars.
Known Issues, TSBs, and Recalls
As of this writing, there are no specific recalls or Technical Service Bulletins (TSBs) from BMW or NHTSA that pertain directly to the exterior quarter moulding of the i8 Coupe. Most owner complaints revolve around general cosmetic issues like rock chips or damage from minor impacts.
Replacement Cost & Difficulty
Replacing the i8's quarter moulding is a complex task that should be approached with caution.
Installation Difficulty: 4.5 out of 5
DIY Feasible: No (Not recommended for beginners)
Estimated Time: 2-3 hours
While the moulding itself is a separate piece, accessing all its mounting points may require the partial removal of surrounding components like the rear bumper cover, taillight, or wheel well liners. The primary risk is damaging the hidden clips or, more significantly, scratching or cracking the expensive carbon fiber reinforced plastic (CFRP) body tub that lies beneath the trim. For these reasons, professional installation by a body shop with experience on BMW i-models is strongly recommended.
| Part / Service | Estimated Cost |
|---|---|
| New OEM Quarter Moulding | $600 - $800 per side |
| New Aftermarket | Not Available |
| Used OEM Quarter Moulding | $150 - $400 per side |
| Shop Labor for Installation | $300 - $500 |
Frequently Asked Questions (FAQ)
Can I install a Coupe quarter moulding on my i8 Roadster?
No, the parts are completely different. The i8 Coupe has the 'flying buttress' C-pillar design, while the i8 Roadster has a different rear body to accommodate the convertible top. The mouldings are not interchangeable.
Is it difficult to replace this moulding myself?
Yes, it is considered a difficult, high-risk job for a DIY mechanic. The trim is attached with many hidden clips and retainers, and there is a significant risk of damaging the expensive carbon fiber body of the car during removal or installation. Professional installation is highly recommended.
My moulding is scratched. Can it be repaired or repainted?
Light surface scratches and swirl marks can often be corrected by a professional detailer using polishing compounds. However, deep scratches or gouges in the plastic are very difficult to repair seamlessly. Repainting is possible, but achieving a perfect high-gloss black finish that matches the factory look can be challenging and costly.
Are the part numbers 51437335812 and 51437407750 for this part?
No. Those part numbers refer to the interior rear quarter trim panels, which are often finished in leather. The exterior 'flying buttress' moulding has different part numbers, such as 51447336437 for the left side.
Technical Specifications
OEM Part Numbers: 51447336437 (Left Side, Driver's Side) 51447336438 (Right Side, Passenger's Side)
Material: Composite Plastic Finish: High-Gloss Black Fitment: 2014-2020 BMW i8 Coupe Only
We Have This Part in Stock
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- BMW i8: