US Patent 7520522 Bicycle frame

The frame includes at its rear portion two bases (12, 13) extending substantially horizontally rearwardly so as to define between them a space for the reception of a rear wheel, and two stays (14, 15) extending obliquely toward one respective end of the bases (12, 13) and being connected thereto at an acute angle by connection elements, a pair of recesses for a rear wheel axle being disposed substantially at the intersection of the stays (14, 15) with the bases (12, 13) . Each recess of the pair of recesses has a first notch with a semicircular bottom (23) provided at one flattened end of a base and a second notch with a semicircular bottom (24) provided at a flattened end of a stay and disposed facing the first notch (23) such that the semicircular bottoms will be aligned with each other.