The physics of cycling speed
At typical road cycling speeds, aerodynamic drag is the dominant resistive force — accounting for roughly 80–90% of total resistance on flat roads. The drag force is proportional to the square of velocity, which means small increases in speed require disproportionately large power increases. This is why aerodynamic position has such a dramatic effect on performance.
Rolling resistance and gradient forces become more significant at lower speeds and on climbs respectively. This model combines all three: aero drag (using position-specific CdA values), rolling resistance (Crr = 0.004 for road tyres), and gravitational grade force.