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 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 (A100), 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 (A200) parallel to the first axis (A100), a component forming a second input component 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 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 (A100), 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 (A200) parallel to the first axis (A100), a component forming a second input component 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 (A100), 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 (A200) parallel to the first axis (A100), a component forming a second input component 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 . <EOS>