Socks Castelli Soudal Quick-Step 2025 Fast Feet 3. There are many so-called aerodynamic socks out there, but the Castelli Fast Feet sock has the development and testing to back up this claim. The few socks that have been tested were probably tested with a static and motionless test because it is easier. But a foot is always in motion, so Castelli created a jig that replicates the movement of the lower leg. Tested on real cyclists to verify the results. This sock can save 2 watts at 50 km/h. The most recent version has an updated cuff fit for greater comfort and aerodynamic gains.

• Fast Feet project by Castelli: for pedaling in hot conditions.
  
• The foot part is based on the Castelli Rosso Corsa sock for shoe comfort.
  
• Polyurethane grip strip at the top to keep the sock in place.
  
• Leg part made with engineered ribbed Lycra® to help detach airflow.
  
• Height: 18 cm.
  
• Color: White.