Rail wagon comprising a loading platform intended to transport a road vehicle equipped with wheels, the wagon comprising an adjustment system for the height-positioning of the wheels of a road vehicle intended to adjust the height of the wheels of the road vehicle to a predetermined height with respect to the loading platform before each transport and for the whole duration of it, such that the transported loaded road vehicle is located at a low level which is greater than or equal to the lower limit of the loading gauge, while respecting the upper limit of the loading gauge, characterised in that an adjustment system is provided for each wheel of the road vehicle, each adjustment system comprising: - a recess made in the loading platform in the region of the site intended for a wheel of the road vehicle, the size of the recess being such that the wheel can be at least partially engaged through the recess; - a supporting device for a wheel mounted on the loading platform in the region of the site intended for the wheel; and wherein: - the supporting device is mounted either directly on the loading platform, or by way of a mobile plate mounted adjustable in longitudinal position on the loading platform; - the supporting device comprises at least one mobile and/or deformable supporting part for supporting the wheel on at least one contact zone such that the wheel is carried by said contact zone in the region of the recess, the movement or the deformation of the at least one supporting part vertically moving the position of the contact zone. an adjustment system for the height-positioning of the wheels of a road vehicle intended to adjust the height of the wheels of the road vehicle to a predetermined height with respect to the loading platform before each transport and for the whole duration of it, such that the transported loaded road vehicle is located at a low level which is greater than or equal to the lower limit of the loading gauge, while respecting the upper limit of the loading gauge, characterised in that an adjustment system is provided for each wheel of the road vehicle, each adjustment system comprising: - a recess made in the loading platform in the region of the site intended for a wheel of the road vehicle, the size of the recess being such that the wheel can be at least partially engaged through the recess; - a supporting device for a wheel mounted on the loading platform in the region of the site intended for the wheel; - a recess made in the loading platform in the region of the site intended for a wheel of the road vehicle, the size of the recess being such that the wheel can be at least partially engaged through the recess; - a supporting device for a wheel mounted on the loading platform in the region of the site intended for the wheel; and wherein: - the supporting device is mounted either directly on the loading platform, or by way of a mobile plate mounted adjustable in longitudinal position on the loading platform; - the supporting device comprises at least one mobile and/or deformable supporting part for supporting the wheel on at least one contact zone such that the wheel is carried by said contact zone in the region of the recess, the movement or the deformation of the at least one supporting part vertically moving the position of the contact zone. - the supporting device is mounted either directly on the loading platform, or by way of a mobile plate mounted adjustable in longitudinal position on the loading platform; - the supporting device comprises at least one mobile and/or deformable supporting part for supporting the wheel on at least one contact zone such that the wheel is carried by said contact zone in the region of the recess, the movement or the deformation of the at least one supporting part vertically moving the position of the contact zone.