Fast Feet 4 Sock There are lots of so-called aero socks out there. But the Castelli Fast Feet 4 Sock has the development and testing to back up the claim. The few socks that have been tested have probably been tested with a static, none moving test because it’s easier. But a foot is always in motion, so we created a jig that replicates the movement of the lower leg. And we tested it on actual riders to verify the results. This sock can save 2 watts at 50 km/h. The newest version has an updated cuff fit for more comfort and aerodynamic gains. Castelli’s Fast Feet project — for maximum aerodynamics Foot portion based on Castelli Rosso Corsa Sock for in-shoe comfort Polyurethane grip strip at top to keep sock in place Leg portion constructed with engineered grooved Lycra® to help detach airflow
