CdA : Aerodynamic drag coefficient
BikeMeasure of a cyclist's wind resistance (Cx × A in m²) : the dominant performance factor above 35 km/h.
CdA (drag coefficient × frontal area, in m²) quantifies the aerodynamic drag of the cyclist+bike system. In Ironman, at 40 km/h, 70-85% of power is spent against wind. A typical CdA in aero position on a triathlon bike is 0.20-0.25 m², versus 0.35-0.40 m² upright. Key levers: bike position (aero bars, torso tilt), TT helmet, smooth skinsuit, covered wheels. Reducing CdA by 0.01 m² is worth approximately +15 W effective power at 40 km/h.
In TriPaced:
In TriPaced, cycling tips include practical advice on aero position and equipment to reduce your CdA without sacrificing comfort : especially critical across the 180 km Ironman bike leg.
Source Grappe F., Cycling and Performance Optimization (De Boeck 2009) - CdA measurement methods (wind tunnel, track)