An improved mechanism for directing movement of a plurality of side-by-side belts in a round baler wherein a bale chamber is optimally configured for bale core formation thereby reducing the need for an aggressive surface on the belts to initiate rotation of the incoming crop material. As the bale expands, the improved mechanism enables the unguided span of belts surrounding the periphery of the bale to be minimized by positioning intermediate guide rolls generally equidistantly from idler rolls bounding the belt guides defining the bale forming chamber. Further, the improved mechanism reduces the friction force between the crop and the belts necessary to initiate crop rolling for bale core formation enabling smooth-surfaced belts to be used which reduce trash generation.