The present disclosure concerns embodiments of an improved wheel assembly for a drive track unit of an all-terrain vehicle that inhibits the accumulation of snow, ice and/or other matter between the track and the wheel assembly. In one implementation, an improved guide wheel assembly for a track unit has a rotatable hub and at least two axially spaced apart guide wheels mounted to the hub that engage the inner surface of an endless track. A flexible and/or deformable sleeve covering the outer surface of the hub is capable of deforming under external pressure applied to the sleeve through contact with snow and/or ice as the vehicle traverses the ground. The deformation of the sleeve is effective to inhibit snow and/or ice from adhering to the sleeve outer surface. Hence, disengagement of the track from the guide wheels caused by accumulated ice and/or snow can be avoided.