Laboratory

Equation

F_drag = ½ · ρ · Cd · A · v²      P = F_drag · v

Definitions

v

Speed — 60–180 km/h, baseline 100

Cd

Drag coefficient — 0.24–0.5, baseline 0.3

A

Frontal area — 1.8–2.6 m², baseline 2.2

ρ

Air density — 1.15–1.25 kg/m³, baseline 1.2

Assumptions

• Speed is converted from km/h to m/s (÷ 3.6) before use.
• Cd, A and ρ are held constant across the speed range. In reality Cd varies with Reynolds number, ride height and yaw.
• Still air, no wind, no road gradient. Rolling resistance and drivetrain losses are not included.
• Educational illustration, not a CFD or wind-tunnel result.

Accuracy limits

• Real Cd varies with Reynolds number, yaw angle, ride height and cooling flow; the model holds it constant.
• Treat results as the idealised cost of drag alone. A real vehicle’s road-load power also includes rolling resistance, drivetrain losses and accessories.
• Numerical accuracy: closed-form arithmetic, exact to floating-point precision. Physical accuracy: indicative only.

Educational illustration, not a CFD result.