Ideal for road racers, time-triallists and performance-focused riders who want a warm-weather aero gain without wearing a full shoe cover.
The FAST FEET 3 SOCK is built for road racing and fast riding in warm conditions, particularly when a Fast Feet TT Shoecover cannot be worn. Castelli’s aero sock design uses an engineered grooved Lycra leg section to help detach airflow around the lower leg, with a claimed saving of 2 watts at 50 km/h.
Underfoot, the sock is based on Castelli’s Rosso Corsa Sock construction for comfortable in-shoe wear. The lower section is thin and breathable, helping manage heat inside close-fitting cycling shoes, while the updated cuff fit is designed to improve comfort and aerodynamic performance.
A polyurethane grip strip at the top helps keep the sock at the correct height while you ride. The Fast Feet project was tested using a moving jig that replicates lower-leg movement and then verified with actual riders, giving this sock a considered aero purpose rather than simply adding a tall cuff. Choose your size by shoe size and take time to smooth the cuff flat when putting it on for the best aerodynamic result.
Engineered grooved Lycra leg
The ribbed Lycra construction is designed to help detach airflow around the lower leg and reduce aerodynamic disruption.
Claimed 2-watt saving
Castelli claims a 2-watt aerodynamic saving at 50 km/h, making the sock suited to racing and time trials where marginal gains matter.
Comfort-focused foot section
The foot portion is based on Castelli’s Rosso Corsa Sock design for a comfortable fit inside cycling shoes.
Warm-weather performance
Designed for riding from 10°C to 38°C, with a thin lower section that helps keep your feet comfortable in warmer conditions.
Secure polyurethane grip
The grip strip at the cuff helps stop the sock from slipping down during hard efforts and long rides.
Updated cuff fit
The revised cuff is intended to improve both all-day comfort and the aerodynamic finish around the lower leg.
Three size options
Available in S/M, L/X and XXL, with sizing based on your cycling shoe size.
General
Dimensions & weight
Materials & construction
Sizing
Aerodynamic performance
Castelli Fast Feet project
An aerodynamic sock platform designed for warm-weather riding, helping reduce drag without requiring a full shoe cover.
Engineered grooved Lycra®
The grooved leg fabric helps detach airflow around the lower leg for improved aerodynamic performance.
Polyurethane grip strip
The grip strip at the top of the sock helps keep it securely in place while you ride.
Rosso Corsa Sock foot construction
The foot section uses the comfort-focused Rosso Corsa Sock design for a more comfortable fit inside the shoe.
