Differential group for a heavy vehicle, said differential group comprising a casing defining a space, a differential and a transmission housed inside said space, said differential being configured to divide an input torque from a drive source to said differential group to a torque of axle shafts (4, 5) of said vehicle coaxial around an axis, said transmission being operatively interposed between said drive source and a carrier of said differential and comprising a first and a second bevel gear (17, 18) and a support shaft, said first and second bevel gear each comprising a crown (17a, 18a) and a pinion (17b, 18b) meshing with each other, said support shaft being connectable to said driving source and being rotationally carried free from said casing, one between said crowns (17a, 18a) and said pinions (17b, 18b) being rotationally coupled to one between said support shaft and said carrier and the other between said crowns (17a, 18a) and said pinions (17b, 18b) being selectively rotationally coupled to the other between said support shaft and said carrier, wherein the other between said crowns (17a, 18a) and said pinions (17b, 18b) can be selectively rotationally coupled to the other between said support shaft and said carrier by means of a selector movable between a first operating condition in which it rotationally couples one of said crowns (17a, 18a) to the other between said support shaft and said carrier and a second operating condition wherein the other couples said crowns (17a, 18a) to the other between said support shaft and said carrier, said selector being controlled by actuator means configured to carry it from the first to the second operating condition, wherein said support shaft carries said pinions (17b, 18b) which are rotationally coupled to it by means of a grooved coupling, said selector being configured to slide, coupled in rotation, to said carrier to alternately couple one of said crowns (17a, 18a) to said carrier, characterized in that said crowns (17a, 18a) being rotationally supported between said casing, said carrier and between them by means of rotating support elements. said differential being configured to divide an input torque from a drive source to said differential group to a torque of axle shafts (4, 5) of said vehicle coaxial around an axis, said transmission being operatively interposed between said drive source and a carrier of said differential and comprising a first and a second bevel gear (17, 18) and a support shaft, said first and second bevel gear each comprising a crown (17a, 18a) and a pinion (17b, 18b) meshing with each other, said support shaft being connectable to said driving source and being rotationally carried free from said casing, one between said crowns (17a, 18a) and said pinions (17b, 18b) being rotationally coupled to one between said support shaft and said carrier and the other between said crowns (17a, 18a) and said pinions (17b, 18b) being selectively rotationally coupled to the other between said support shaft and said carrier, wherein the other between said crowns (17a, 18a) and said pinions (17b, 18b) can be selectively rotationally coupled to the other between said support shaft and said carrier by means of a selector movable between a first operating condition in which it rotationally couples one of said crowns (17a, 18a) to the other between said support shaft and said carrier and a second operating condition wherein the other couples said crowns (17a, 18a) to the other between said support shaft and said carrier, said selector being controlled by actuator means configured to carry it from the first to the second operating condition, wherein said support shaft carries said pinions (17b, 18b) which are rotationally coupled to it by means of a grooved coupling, said selector being configured to slide, coupled in rotation, to said carrier to alternately couple one of said crowns (17a, 18a) to said carrier, characterized in that said crowns (17a, 18a) being rotationally supported between said casing, said carrier and between them by means of rotating support elements.