DESCRIPTION
The Castelli Fast Feet 4 Sock is a high-performance aerodynamic cycling sock developed using Castelli's Fast Feet Project. Designed and tested in real-world riding conditions, it helps reduce aerodynamic drag while maintaining exceptional comfort. The foot section is based on the proven Rosso Corsa Sock for superior in-shoe comfort, while the grooved Lycra® leg section improves airflow and minimizes drag. Ideal for road racing, time trials, and high-speed training. 

FEATURES
Developed through Castelli's Fast Feet Project for maximum aerodynamic performance 
Proven to save approximately 2 watts at 50 km/h 
Foot portion based on the Castelli Rosso Corsa Sock for exceptional comfort 
Engineered grooved Lycra® leg construction helps improve airflow 
Polyurethane grip strip at the top keeps the sock securely in place 
Lightweight and highly breathable construction 
Race Fit for high-performance cycling 
Suitable for road racing, time trials, and fast training rides 
Recommended temperature range: 10°C–38°C 

SPECIFICATIONS
Brand: Castelli 
Model: Fast Feet 4 Sock 
Model Code: 4526030-025 
Color: Rosa Giro 
Gender: Unisex 
Fit: Race Fit 
Sock Height: Aero High Cuff 
Grip: Polyurethane Grip Strip 
Foot Construction: Rosso Corsa Sock Base 
Leg Construction: Engineered Grooved Lycra® 
Recommended Temperature: 10°C–38°C 
Approximate Product Weight: 0.05 kg (50 g) 
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SIZE CHART
Size    EU Shoe Size    US Men's    US Women's
S/M    36–39    4–7    5.5–8.5
L/XL    40–43    7.5–10.5    9–11.5
XXL    44–47    11–14