Abstract: A right crank arm assembly for a bicycle, comprises a right crank arm, a first annular element directly coupled with said crank arm at at least one first coupling portion of said first annular element and at least one second annular element coupled with said crank arm and of a smaller size than said first annular element. The first annular element comprises a toothing that extends radially towards the outside along a primitive circumference having a predetermined diameter. Said at least one first coupling portion is entirely contained in a first area extending radially towards the outside starting from an ideal circumference having a diameter at least equal to ? of said predetermined diameter. Such an annular element constitutes the front sprocket of the crank arm assembly of the present invention and consists of a simple toothed band. Such a front sprocket is particularly light in weight.