While I was visiting Specialized a few weeks back for the launch of the S-Works Venge ViAS, I expressed skepticism about the company’s claims that shaving your legs could save 60-90 seconds over 40km. “Well, find somebody with hairy legs and bring them in here,” Specialized’s Mark Cote told me.
As luck and Colorado’s long rainy spring would have it, I hadn’t shaved since the end of cyclocross season. And thus, in a few minutes I found myself in guinea-pig mode inside Specialized’s wind tunnel.
Cam Piper, Specialized’s aero R&D engineer, recorded my aero drag while pedaling, taking the average for 60 seconds. Unlike most wind tunnels, Specialized’s was built specifically for cycling, and the resolution goes down to 0.0005m2. For context, a rider on a bike is usually in the 0.25m2 to 0.55m2 range for CdA. What the heck is CdA, you ask? It is the measurement of an object’s drag coefficient (Cd) multiplied by its frontal area (A). A smaller number means more aero. Here is a good explanation of CdA.
You’ve probably heard people talk about a rider’s power-to-weight ratio being a key determinant in performance, and it is – especially on steep roads. But a rider’s power-to-drag ratio is also a huge factor in racing. Time trialing is the most obvious example, but even look at how low Mark Cavendish gets while sprinting; he is maximizing his power-to-drag.
Anyhow, my CdA with hairy legs on a Venge ViAS with a skinsuit and an Evade aero helmet was 0.271m2. Shaving my legs and getting back on the bike in the tunnel, my CdA dropped to 0.259 in the same position. (Relatedly, my CdA on a Tarmac with a standard jersey and bibs and a Prevail helmet was 0.308, also in the same position with hands on the hoods and elbows partially bent.)
Piper (at right) measuring my CdA while pedaling. Since the legs are obviously in motion, they create effectively create a larger frontal area than if I was just sitting on the bike without pedaling
The total real-world savings of shaving my legs? Some 48 seconds over 40km.
“A general range that we see for savings is between 40 and 90 seconds saved over 40km,” Piper said, adding that a rider’s speed does not affect that time savings. A faster rider will face more air resistance but is out there for less time while a slower rider will face less resistance but will be riding longer and still save the same amount of time.
“Next time we’ll have to shave your arms,” Piper said, not entirely joking. "The savings there is about a quarter of the legs, but still a surprise for us. Mine were about 15 seconds/40km, and I don’t have much hair on my arms.”
Yes, shaving the legs is an old roadie tradition. But now I have a better answer about why I do it
To give some more context in terms of time over a 40km, the S-Works skinsuit itself is worth about 96 seconds compared with standard bibs and jersey, Specialized claims, and the Evade aero helmet is worth another 46 seconds over a regular helmet.
Specialized claims the new S-Works Venge ViAS Di2 bike can save you 120 seconds over 40km. (My testing found a savings of 142 seconds for ViAS, skinsuit and Evade combined over 20km; if half the savings can be attributed to the bike, this 120 seconds over 40km seems reasonable.) The S-Works Venge ViAS will retail for $12,500 / £8,500. A razor and shaving cream? More like $5 / £3.