Drivetrain Efficiency
Drivetrain efficiency describes how much input power reaches a defined mechanical output after losses in the components included in the test boundary.
Define the boundary first
A motor-and-inverter result may begin at the inverter's DC input and end at the motor shaft. A drive-unit result can also include reduction gears, bearings, seals, lubrication, pumps, and the differential. Battery-to-wheel efficiency includes still more of the vehicle.
Efficiency changes with speed, torque, temperature, lubricant condition, and control strategy. It should therefore be expressed as an operating map or duty-cycle result, not treated as one permanent percentage. Figures with different boundaries cannot be compared directly. EV motor testing and ratings
Published values should also state whether power flows forward during propulsion or backward during regeneration, because the two directions can have different losses.