Aero leg covers: what you actually gain by covering the leg

aerodinámicaJuly 23, 20265 min readBorja Alfaraz

Aerodynamics

18-44 s

Saving over 40 km at 300 W depending on whether you shave only or also add aero leg covers.

Equivalent to a CdA reduction of 0.004 to 0.010 m². Computed with the AthletePro physics engine.

Abstract. This article quantifies the aerodynamic effect of leg-surface interventions —shaving and aero leg covers/sleeves— on time-trial performance. Their magnitude is placed in the context of total CdA and contrasted with industry-reported figures, noting the range of uncertainty.

Moving legs are a disproportionate source of drag: they rotate, expose changing surfaces to the flow and generate turbulence. Acting on them —smoothing the hair or covering them with a calculated aero fabric— therefore reduces CdA measurably. The question is not whether it helps, but how much.

How much, in numbers

Over a 40 km time trial at 300 W (starting CdA 0.240), the AthletePro physics engine yields:

Intervention	Typical CdA delta	Saving over 40 km
Leg shaving	−0.004	≈ 18 s
Aero leg covers / sleeves	−0.006	≈ 26 s
Both combined	−0.010	≈ 44 s

Leg shaving was popularised as an aerodynamic gain by a wind-tunnel test publicised by Specialized (2014), which reported notably high figures. Independent studies place it in a more conservative range (~5-7 W, of the order of 15-30 s over 40 km), and the exact magnitude remains a matter of methodological debate. Aero leg covers, with calculated-roughness fabric, add an effect of the same order.

Perspective. A 40 s saving over 40 km is real and free to maintain, but small next to position (minutes) or the skinsuit (1-3 min). Aero leg covers are a legitimate marginal gain: added at the end, once the big items are solved, not before.

Conditions for it to pay off

Fit. Like all aero textiles, it only works taut and wrinkle-free.
Speed. The effect grows with speed; below 30 km/h it is practically negligible.
Legality. In UCI competition, covering the leg with separate garments may not be allowed; check the regulations.

In AthletePro you can reflect these gains as a CdA adjustment on the bike and see the effect on predicted time before deciding whether they are worthwhile for your event.

References

Specialized Win Tunnel (2014). Leg shaving aerodynamic test. Divulgación técnica (no revisada por pares); cifra objeto de debate metodológico.
García-López, J., et al. (2008). Reference values and improvement of aerodynamic drag in professional cyclists. Journal of Sports Sciences, 26(3), 277-286.
Debraux, P., Grappe, F., Manolova, A. V., & Bertucci, W. (2011). Aerodynamic drag in cycling: methods of assessment. Sports Biomechanics, 10(3), 197-218.