The MINI John Cooper Works (F67) convertible is a 1,450–1,500 kg (≈ 3,197–3,307 lb) go-kart on steroids. While agile, its factory iron brakes are the first performance bottleneck to appear when the car is pushed through mountain passes or technical circuits.
The Struggle
On a short-wheelbase hot hatch like the F67, the front brakes manage nearly 80% of the stopping force. Physics reveals three major weak points in the stock iron hardware:
- Thermal Saturation: Repeated high-G stops push iron rotors past their heat-sink capacity, causing the pedal to go "long."
- Front-End Inertia: Heavy iron discs contribute significantly to unsprung mass, which blunts the steering's "go-kart" precision.
- Corrosive Contamination: OEM pads generate sticky, dark dust that bakes onto wheels and oxidizes instantly after washing.
Technical Specification
This configuration replaces the stock floating system with a high-performance 355 mm (14.0 in) Carbon-Ceramic (C/SiC) front kit paired with AP Racing motorsport calipers.
| Vehicle | MINI JCW F67 (Convertible) |
|---|---|
| Front Calipers | AP Racing CP9660 (6-Piston Fixed) |
| Front Rotors | StopFlex C/SiC (355 x 32 mm) |
| Weight Saving | ≈ 55% Reduction vs. Steel |
| Pad Material | CCB-Optimized Ceramic Compound |
Compatibility Redline
A rotor-only swap is only possible if your MINI already runs fixed multi-piston calipers and a rotor of at least 330mm. For standard floating-caliper JCWs, a Full Kit (calipers + brackets + CCB rotors) is the required path for safety.
Engineering & Surface Treatment
1. Proprietary Bright & Glossy Coating
A common issue with many carbon ceramic discs is their dull or porous look after use. StopFlex uses a proprietary ceramic top coat that keeps the rotor surface bright and glossy behind the wheel. This prevents the C/SiC body from oxidizing and ensures zero surface rust after car washes, maintaining a premium look.
2. Stable Friction Coefficient (**μ**)
Factory iron setups lose bite as heat builds. StopFlex rotors maintain a stable 0.44–0.52 μ window. Crucially, even at extreme temperatures of 900 °C (≈ 1,650 °F), the friction coefficient **μ** remains above 0.40, where iron would suffer catastrophic fade.
3. Unsprung Mass Dynamics
Removing ≈12kg+ (≈26 lbs) of unsprung mass from the front axle allows the dampers to control wheel movement with far greater precision. This yields a noticeably more eager turn-in and improved tracking over mid-corner bumps.
4. 3D Continuous Long-Fiber Skeleton
StopFlex utilizes a 3D Continuous Long-Fiber skeleton with a density of 1.6 g/cm³ and a tensile strength of 140 MPa. This architecture ensures a street service life of up to 300,000 km (≈ 186,000 mi).
Installation Gallery
In-Depth MINI JCW F67 FAQ
Q: Why choose an AP 9660 + StopFlex kit over just pads and fluid?
Pads and fluid can help with bite, but they cannot address the thermal mass limitations of iron or the flexibility of stock floating calipers. The AP CP9660 provides a rigid body that eliminates pedal "mush," while the CCB rotors provide thermal headroom that iron simply cannot reach.
Q: Will this 355mm kit clear factory 18-inch wheels?
Yes. The 355mm rotor is sized specifically for 18-inch performance wheels. However, the fixed caliper requires adequate spoke clearance (X-factor). We recommend a template check to ensure the wheel offset allows for proper caliper clearance.
Q: How do carbon-ceramic brakes handle wet weather?
Unlike iron rotors which form a rust layer when wet, C/SiC rotors are chemically inert. This means zero surface rust after washing and more consistent braking in the rain, without the "cleaning" stop required for rusty iron discs.
Q: Is there any long-term maintenance benefit?
Beyond the extreme service life, the two-piece floating design allows for ring-only replacement. Additionally, because CCBs run cooler and generate less corrosive dust, wheel bearings and suspension components are subjected to less chemical wear.
