Abstract: A speed varying sprocket wheel assembly for use in combination with a transmission chain comprises a plurality of sprocket wheels with different number of teeth and mounted coaxially adjacent to one another so as to permit the chain to be shifted from one to the other, each tooth being defined by a tip face, two circumferential sides, and two axial sides and having a notch at a corner formed by the tip face, one of the circumferential sides and one of the axial sides so that the tip face has a circumferential edge with a reduced circumferential dimension and an axial edge with a reduced axial dimension, the notches being arranged at the forward side of the teeth relative to the direction of the rotation of the sprocket wheels.