lower guide 80 is positioned where the pulley 82 aligns with the teeth of the chain ring where the chain exits from the teeth of the chain ring during forward pedaling due to its position the lower guide 80 ensures that the chain remains engaged with the chain ring over a larger part of the chain ring 39 s perimeter than if the chain merely extended from the chain ring at the lowest point of the chain ring the lower guide 80 also serves to prevent derailment especially during backpedaling still referring to fig3 the semi circumferential portion 53 of the guard 50 extends radially downwardly and outwardly past the chain ring along that portion of the chain ring most likely otherwise to suffer damage from underside impacts with obstacles as the bicycle moves forward preferably the configuration of this portion of the apparatus is consistent with the configuration in u s pat no 7 066 856 which is incorporated herein by reference the straight portion 55 of the guard additionally protects the portion of the chain and chain ring that extends just rearward of the vertical centerline of the bottom bracket the straight portion 55 of the guard further protects the lower guide 80 from damage from underside impacts still referring to fig3 the screw and nut 89 that attaches the lower guide and idler pulley not visible in fig3 to the bracket 20 also attaches the guard 50 to the bracket 20 providing support to the straight portion 55 of the guard and adding strength rigidity and structural integrity to the assembly as.