Ideal for road racers, time-triallists and performance-focused riders who want a comfortable aero sock for warm conditions.
The Castelli Fast Feet 3 Sock is an aero cycling sock for road racing and warm-weather riding, particularly when a Fast Feet TT Shoecover cannot be worn. The lower foot section is based on Castelli’s Rosso Corsa Sock, giving you a comfortable in-shoe feel, while the engineered grooved Lycra leg is designed to help detach airflow around the moving lower leg.
A polyurethane grip strip at the cuff helps keep the sock at the correct height during hard efforts. The foot section is thin and breathable, with minimal seams to help reduce hotspots inside your shoe, while the Lycra upper delivers the close race fit expected from an aero sock.
Castelli developed and tested the design using a moving jig that replicates lower-leg movement, then verified it with actual riders. The published claim is 2 watts saved at 50 km/h. For best results, pull the sock on smoothly and make sure the cuff and gripper sit flat against your leg. At 51 g per pair, this is a focused upgrade for racing, time trials and fast group rides where every marginal gain counts.
Engineered grooved Lycra
The ribbed leg construction is shaped to help detach airflow around your moving lower leg and support aerodynamic performance.
Claimed 2-watt saving
Castelli claims a 2-watt aerodynamic saving at 50 km/h, making this a practical marginal-gains upgrade for racing.
Rosso Corsa-based foot section
The foot portion is based on Castelli’s Rosso Corsa Sock for comfortable wear inside your cycling shoes.
Secure polyurethane grip strip
The cuff grip helps keep the sock in place and maintains a consistent aero position during hard riding.
Warm-weather design
Designed for riding from 10°C to 38°C, with a lightweight foot section suited to hotter conditions.
Race fit and sizing
The close race fit is available in S/M, L/X and XXL, with sizing based on your shoe size.
Updated cuff fit
The revised cuff is designed to improve comfort while supporting the sock’s aerodynamic performance.
General
Dimensions & weight
Materials & construction
Sizing
Performance
Castelli Fast Feet project
Designed for warm-weather riding, this aero sock helps reduce drag around the lower leg when you are racing or chasing speed.
Engineered grooved Lycra®
The grooved leg fabric is shaped to help detach airflow from the moving lower leg.
Polyurethane grip strip
The grip strip at the top of the sock helps keep the cuff securely in place during hard riding.
Rosso Corsa foot construction
The foot section is based on Castelli’s Rosso Corsa Sock for a comfortable fit inside the cycling shoe.
