Abstract: A safety disc assembly for a bicycle having a wheel with an axle, rim and a plurality of radially extending spokes between the axle and rim. The safety disc assembly includes a first and second wheel disc, with each wheel disc adapted to be mounted on a bicycle wheel intermediate the rim and the axle on oppositely disposed sides of the spokes. The first and second wheel disc each includes a pair of co-acting disc members, with each one of the disc members including a contoured outer perimeter and a contoured inner perimeter with a terminal wall extending therebetween. The contoured perimeters are adapted to extend in spaced relationship to the rim and to the axle, respectively. Alignment structure for permitting abutting engagement between each pair of the disc members on the first and second wheel discs is provided so as to permit the disc members to be assembled on the wheel without the removal thereof from the bicycle.