Work out drag coefficient effect instantly with clear inputs, formula shown and shareable results.
Drag power is half rho Cd A v cubed, so it is proportional to Cd. Cutting Cd from 0.32 to 0.28 saves 12.5% of drag power, but the fuel saving is smaller because rolling resistance and driveline losses do not change.
Drag power
P = 0.5 x rho x Cd x A x v^3; saving is proportional to the change in Cd
Around 70-80 km/h for a typical car. Below that rolling resistance dominates and aerodynamic improvements barely register.
0.30-0.35 for a modern hatchback, 0.24-0.28 for an aerodynamic saloon or EV, and 0.35-0.45 for an SUV or van.