A transmission unit for motor vehicles, comprising: - an input shaft adapted to be connected to the motor, - an output shaft adapted to be connected to at least one driving wheel of the vehicle, - a first transmission member adapted to connect the input shaft to a first driving shaft, wherein the first transmission member comprises a gear which comprises a first toothed wheel rotating as a unit with the input shaft and a second toothed wheel, which rotates as a unit with the first driving shaft and engages with the first toothed wheel, - a first discontinuous speed gear adapted to connect a first driven shaft with the output shaft, - a first clutch interposed between the first driving shaft and the first driven shaft, - a second transmission member adapted to connect the input shaft to a second driving shaft, wherein the second transmission member comprises a gear, which makes a higher gear ratio than the gear ratio of the gear of the first transmission member and which comprises a first toothed wheel rotating as a unit with the input shaft and a second toothed wheel, which rotates as a unit with the second driving shaft and engages with the first toothed wheel, - a second discontinuous speed gear adapted to connect a second driven shaft with the output shaft, - a second clutch interposed between the second driving shaft and the second driven shaft, - a third transmission member adapted to connect the input shaft to a third driving shaft, wherein the third transmission member comprises a gear, which makes a higher gear ratio than the gear ratio of the gear of the second transmission member and which comprises a first toothed wheel rotating as a unit with the input shaft and a second toothed wheel, which rotates as a unit with the third driving shaft and engages with the first toothed wheel, - a third discontinuous speed gear adapted to connect a third driven shaft with the output shaft, and - a third clutch interposed between the third driving shaft and the third driven shaft said transmission unit being characterised by the fact that it comprises: - a fourth transmission member adapted to connect the input shaft to a fourth driving shaft and comprising a gear, which comprises the first toothed wheel of the first transmission member, rotating as a unit with the input shaft, and a second toothed wheel, which rotates as a unit with the fourth driving shaft and engages with the first toothed wheel through a third toothed wheel, - a fourth discontinuous speed gear adapted to connect a fourth driven shaft with the output shaft, and - a fourth clutch interposed between the fourth driving shaft and the fourth driven shaft. - an input shaft adapted to be connected to the motor, - an output shaft adapted to be connected to at least one driving wheel of the vehicle, - a first transmission member adapted to connect the input shaft to a first driving shaft, wherein the first transmission member comprises a gear which comprises a first toothed wheel rotating as a unit with the input shaft and a second toothed wheel, which rotates as a unit with the first driving shaft and engages with the first toothed wheel, - a first discontinuous speed gear adapted to connect a first driven shaft with the output shaft, - a first clutch interposed between the first driving shaft and the first driven shaft, - a second transmission member adapted to connect the input shaft to a second driving shaft, wherein the second transmission member comprises a gear, which makes a higher gear ratio than the gear ratio of the gear of the first transmission member and which comprises a first toothed wheel rotating as a unit with the input shaft and a second toothed wheel, which rotates as a unit with the second driving shaft and engages with the first toothed wheel, - a second discontinuous speed gear adapted to connect a second driven shaft with the output shaft, - a second clutch interposed between the second driving shaft and the second driven shaft, - a third transmission member adapted to connect the input shaft to a third driving shaft, wherein the third transmission member comprises a gear, which makes a higher gear ratio than the gear ratio of the gear of the second transmission member and which comprises a first toothed wheel rotating as a unit with the input shaft and a second toothed wheel, which rotates as a unit with the third driving shaft and engages with the first toothed wheel, - a third discontinuous speed gear adapted to connect a third driven shaft with the output shaft, and - a third clutch interposed between the third driving shaft and the third driven shaft - a fourth transmission member adapted to connect the input shaft to a fourth driving shaft and comprising a gear, which comprises the first toothed wheel of the first transmission member, rotating as a unit with the input shaft, and a second toothed wheel, which rotates as a unit with the fourth driving shaft and engages with the first toothed wheel through a third toothed wheel, - a fourth discontinuous speed gear adapted to connect a fourth driven shaft with the output shaft, and - a fourth clutch interposed between the fourth driving shaft and the fourth driven shaft.