Chain-rings set for bicycle including a first chain-ring and a second chain-ring, this latter formed by segments, which includes displacement means with axial component of the segments with respect to the first chain-ring such that they can be moved a the chain free zone ZLC and shift the chain among chain-rings, where the axial displacement means are formed by guiding means configured for guiding the segments such that the relative movement of the teeth of the segments with respect to the small chain-ring in its displacement from a first disengagement configuration to a second engagement configuration has a tangential component opposite to the forward direction.