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CDA (COEFFICIENT OF DRAG × AREA)

The aerodynamic drag coefficient multiplied by the rider's frontal area — the single number that describes how much air resistance a rider generates at a given speed.

Amateur road riders typically have CdA between 0.30-0.40 m²; elite time trialists can reach 0.18-0.22 m². Above roughly 20 mph, CdA dominates total drag — reducing CdA by 10% is worth roughly as much as a 10% FTP increase at race pace. Measurable via wind tunnel, aero sensors (Notio, Aerolab), or protocol-based field testing. The fastest CdA gains for amateurs are almost always positional: narrower elbows, lower head, flatter back.