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.
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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.)
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