Cycling Tool
CdA Drag Estimator
Reverse-estimate approximate CdA from steady segment data to compare position and equipment changes quickly.
Steady Segment Data
km/h
W
%
km/h
kg
kg
Estimated CdA
0.280
Good road-bike position
Speed Sensitivity
| CdA change | Same-power speed | 40 km time change |
|---|---|---|
| -0.030 | 39.4 km/h | save 02:12 |
| -0.015 | 38.7 km/h | save 01:05 |
| +0.015 | 37.4 km/h | slower 01:02 |
| +0.030 | 36.8 km/h | slower 02:02 |
Theory
CdA is the product of drag coefficient and frontal area. At high speed on flat roads, aerodynamic drag is often the largest power demand because aero power scales with relative wind speed squared times riding speed (double the speed, roughly 8x the aero power). Martin et al. (1998) validated a power model that separates gravity, aerodynamic drag and rolling resistance; this tool inverts the same model to estimate CdA. The estimate needs a steady segment, stable power, known wind and a well-calibrated power meter — ideally a long straight road with no wind.
Sources: Martin et al. 1998, J Appl Biomech