A powertrain system for driving at least one wheel of a vehicle, comprising: - a motor having an output shaft; - a transmission system between the motor and a drive shaft connected to said wheel, the transmission system comprising two epicyclic gear trains (100, 200) each including the following components: a ring, a sun, a planet carrier and planet gears, wherein: - a first epicyclic gear train has a first axis, a component forming a first input component connected to the motor output shaft, and a component forming a first output component; - a second epicyclic gear train has a second axis parallel to the first axis, a component forming a second input component (201, 205) meshing with the first output component, and a component forming a second output component configured to be connected to the drive shaft; characterized in that the ring, an intermediate part slidably mounted on the outer part of the ring, or the sun of one of the epicyclic gear trains is movable, preferably parallel to the first and second axes (A100, A200), between at least: - a first position, in which the motor is able to transmit torque to the drive shaft according to a first gear ratio; and a second position, in which the motor is able to transmit torque to the drive shaft according to a second gear ratio; or between: - at least one position in which the motor is able to transmit torque to the drive shaft; - and a neutral position in which no torque can be transmitted from the motor to the drive shaft. - a motor having an output shaft; - a transmission system between the motor and a drive shaft connected to said wheel, the transmission system comprising two epicyclic gear trains (100, 200) each including the following components: a ring, a sun, a planet carrier and planet gears, wherein: - a first epicyclic gear train has a first axis, a component forming a first input component connected to the motor output shaft, and a component forming a first output component; - a second epicyclic gear train has a second axis parallel to the first axis, a component forming a second input component (201, 205) meshing with the first output component, and a component forming a second output component configured to be connected to the drive shaft; - a first epicyclic gear train has a first axis, a component forming a first input component connected to the motor output shaft, and a component forming a first output component; - a second epicyclic gear train has a second axis parallel to the first axis, a component forming a second input component (201, 205) meshing with the first output component, and a component forming a second output component configured to be connected to the drive shaft; characterized in that the ring, an intermediate part slidably mounted on the outer part of the ring, or the sun of one of the epicyclic gear trains is movable, preferably parallel to the first and second axes (A100, A200), between at least: - a first position, in which the motor is able to transmit torque to the drive shaft according to a first gear ratio; - a first position, in which the motor is able to transmit torque to the drive shaft according to a first gear ratio; and a second position, in which the motor is able to transmit torque to the drive shaft according to a second gear ratio; or between: - at least one position in which the motor is able to transmit torque to the drive shaft; - and a neutral position in which no torque can be transmitted from the motor to the drive shaft. - at least one position in which the motor is able to transmit torque to the drive shaft; - and a neutral position in which no torque can be transmitted from the motor to the drive shaft.