CdA Calculator — Estimate Drag Coefficient Area

CdA Estimation

This rearranges the Martin et al. (1998) road-cycling power model. A power meter reads power at the pedals, so we first remove the drivetrain loss (≈2.4%, i.e. 97.6% efficiency) to get power delivered to the road, then strip out the rolling and gravity terms — whatever is left is spent on aerodynamic drag:

• P_road = P_pedal × 0.976
• P_aero = P_road − P_rolling − P_gravity
• CdA = 2 × P_aero / (air_density × v³)

This assumes steady-state conditions — flat, windless laps with accurate power and speed data. Average several runs to cancel residual wind.