The Castelli Fast Feet aero socks are lightweight and breathable, making them a pleasure to wear during hard efforts. Although the aero gains aren't likely to be huge, given how comfortable they are, you might as well reap them. However there is one caveat; if wearing the socks for over six hours, the silicon gripper can start to cut in.
Potential for aero gains
Looks the part
Very well ventilated
Silicon gripper keep them in place
Gripper can cut in after 6 hours
By Stefan Abram published
Castelli's fast feet aero cycling socks are constructed with “engineered grooved Lycra to help detach airflow,” with the intention of improving aerodynamics for faster riding.
The gains fall very much into the “marginal” end of the spectrum, slipping these on won't have you suddenly dropping your mates on the flat. But if you've got a little bit of cash to spare, it certainly can't hurt - and there has been a fairly wide take up of this style of sock by the pro peloton, especially in TTs.
The construction: Castelli Fast Feet aero socks
The lower portion of the sock is based on Castelli's time-proven Rosso Corsa, with the aim to provide comfortable coverage and good ventilation. Around the ankle, the make-up changes to that distinctive grooved Lycra, which has a feel similar to a jersey or set of bib shorts.
There's a large focus on breathability, with Castelli recommending using these socks when the conditions are too warm for their aero shoe covers – which have the same grooved profile on the legs and also smooth out the surface of the shoes, causing lesser disruption to the airflow.
The socks extend 18cm above the center of my ankle joint. This is longer than I would typically go for in a sock, but in this case I'd say it's a good thing – you’re paying a premium for grooved Lycra, so it wouldn't do to skimp on that. On the inside of the cuff there's a silicon gripper to keep the socks in place and to prevent them from falling down.
Something to note about the silicon gripper is that it can pick up fluff from other clothes. Pulling this off isn't exactly arduous, but it's not something you'd particularly want to spend your time doing. However, I found this was easily solved by making sure to turn the sock you're folding it with inside out, so the silicon gripper is kept on the inside and not brushing up against any other fabrics.
the Fast Feet socks lived up well to their billing as aero optimization for hot conditions. Wearing these for Zwift races, the lower portion of the sock did an excellent job of quickly wicking away sweat and allowing my feet to breath. While they did end up a little damp by the end, there was at least no feeling of clamminess.
Even on long Sunday rides, the lower portion of the sock never felt uncomfortable inside my shoes, with no awkward seams causing hotspots or irritations.
The upper portion of the socks wasn't quite as breathable as the lower, so those seeking the maximum in ventilation would be better served by a different sock. But my lower legs don't tend to get as hot as my feet, so this never caused me to feel uncomfortable. It would have to be outrageously warm before getting to the point that I'd feel that the Lycra portion is too hot.
The silicon gripper did a great job at keeping the socks at the right height and they never once slipped down. However, I did find that after wearing them continuously for over six hours that the gripper did start to cut into my skin, leaving a little mark on the inside of my left leg that took a few days to fade away.
It's not too much of a criticism though, as the majority of their application will be in shorter efforts. Plus generally, if a ride is over six hours and yet demands the application of aero socks, there's probably going to be enough other discomfort in the name of aero that a little bit of digging in from a cuff would be pretty low on the list of concerns.
As aero socks go, the Castelli Fast Feet are on the pricier side at £36. Huub’s Aero Socks, Conder’s Aero Socks and Nopinz’ Flow-Sock each come in at £30, £24.99 and £28.99, respectively.
But having not yet tested those three, we can’t comment on how they compare for comfort – other than the gripper cutting in after six hours, the Castelli socks were an utter pleasure to wear.
Starting off riding mountain bikes on the South Downs way, he soon made the switch the road cycling. Now, he’s come full circle and is back out on the trails, although the flat bars have been swapped for the curly ones of a gravel bike.
Always looking for the next challenge, he’s Everested in under 12 hours and ridden the South Downs Double in sub 20. Although dabbling in racing off-road, on-road and virtually, to date his only significant achievement has been winning the National Single-Speed Cross-Country Mountain Bike Championships in 2019.
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