Drive roll (6) and auxiliary drive means (3) for a trailer provided with a drive roll of this type. The drive roll (6) is substantially cylindrical in its construction and comprises a number of first shallow grooves (7), extending in the longitudinal direction thereof, and second deep grooves (8). Comparatively sharp cams (9) are delimited therebetween. The first shallow grooves are hollow and, more particularly, arc of a circle-shaped. The depth (d1) is such that during pressing against the tyre, not only the cams but also the base of the shallow grooves may enter into contact with the tyre. This configuration provides a self-cleaning effect, i.e. dirt trapped in the grooves is pushed outward by the interaction between the tyre and roll.