Abstract: An axle drive unit, for use in a tri-axle drive, comprises a casing (10) with an input member (18) at one end connected to the planet carrier (30) of a spur gear epicyclic differential gear whose sun gear (28) is connected to a tubular shaft (43) and then by gears (47, 56) to the input of an inter-wheel differential gear. The annulus gear (27) of the epicyclic differential gear is connected to a driving shaft (40) extending through the tubular shaft (43) and then to an output member (19) at the other end of the casing. The epicyclic differential gear gives a torque output to the output member (19) of approximately twice that to the inter-wheel differential gear in the unit, so that when the output member (19) is connected to a further inter-axle differential gear in a tri-axle drive, torque is approxiamately equally split between all three axles.