A power assist vehicle (10) according to claim 1 comprises a drive wheel (18) input means (22) for receiving a driving torque from a user a motor (24) a transmission, assembly (23) coupling the motor to the drive wheel to permit the motor to drive the drive wheel and coupling the input means to the drive wheel so as to permit the input means to simultaneously drive the drive wheel and a control system programmed with at least one control map defining a desired dynamic of the vehicle and programmed with a desired mass parameter and a desired drag parameter, the control system utilizing said control map and measured values of said driving torque from said user and an actual velocity to determine a desired velocity and employs a single-axis velocity servo loop to control the motor to reduce an error component between said actual velocity and said desired velocity.
