Castelli Fast Feet 4 Sock White - 2X-Large

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From BikeTiresDirect

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. This sock can save 2 watts at 50 kmh. The newest version has an updated cuff fit for more comfort and aerodynamic gains. | Castelli Fast Feet 4 Sock White - 2X-Large