Carbon fiber was first used in the aerospace industry.After time goes carbon fiber is widely used in various industries.In bicycle industry,carbon fiber is the primary material used in high-performance carbon rims due to its exceptional strength-to-weight ratio, stiffness, and aerodynamic properties.Here’s a detailed breakdown of how carbon fiber is utilized in carbon rims:
1.Types of Carbon Fiber Used
A. Raw Materials
PAN-based Carbon Fiber: Most common (e.g., Toray T700/T800/T1000), offering a balance of strength and affordability.
Pitch-based Carbon Fiber: Used in ultra-high-modulus applications (e.g., Mitsubishi Dialead), but more expensive.
B. Fiber Formats
Unidirectional (UD) Carbon: Fibers run parallel for maximum stiffness in load-bearing areas (e.g., spoke beds, brake tracks).
Woven Carbon (2D/3D): Crosshatch weaves (e.g., 3K, 12K) for impact resistance and torsional rigidity.
Hybrid Layups: Combined with Kevlar or fiberglass for durability (common in gravel/MTB rims).
2. Key Components of a Carbon Rim
A. Structural Layers
Outer Shell: Woven carbon for impact resistance (e.g., 3K weave for cosmetic finish).
UD Main Body: Unidirectional fibers aligned with rim shape for optimal stiffness.
High-Stress Reinforcements:
Spoke Holes: Extra UD layers or titanium inserts to prevent cracking.
Bead Hook (if hooked): Additional carbon wraps to secure the tire.
Brake Track (rim-brake rims): Heat-resistant resin + ceramic coatings.
B. Core Technologies
Hollow Core Design: Internal cavities or foam cores reduce weight while maintaining strength.
Toroidal Shape: Aerodynamic profiles (e.g., Zipp’s ABLC dimples) optimize airflow.
Hookless vs. Hooked: Hookless rims rely on reinforced sidewalls instead of traditional hooks.
3. Manufacturing Process
Layup: Carbon sheets are cut and stacked in molds with precise fiber orientations.
Resin Infusion: Epoxy resin binds fibers (hand-laid or automated pre-preg).
Curing: High pressure/temperature in an autoclave or oven.
Post-Processing: CNC machining for spoke holes, brake tracks, and surface finishing.
4. Performance Advantages
Weight: 30–50% lighter than aluminum rims (e.g., 1,200g vs. 1,800g for a wheelset).
Stiffness: Higher lateral rigidity for better power transfer.
Aerodynamics: Deeper profiles (50mm+) reduce drag at high speeds.
Durability: Fatigue-resistant (no metal-style fatigue cracks).
5. Limitations
Cost: High-end carbon rims are 2–5x more expensive than aluminum.
Impact Sensitivity: Hard hits can cause delamination (less forgiving than metal).
Heat Management: Rim-brake carbon rims require careful descending to avoid resin failure.
