Rear suspension device for a bicycle with three pivots, each with an axis of rotation an axial compression shock absorber, a linkage unit, a sensor unit and a magnet. The axes of rotation are parallel to each other and the axial compression shock absorber has a first end attached to the first pivot and a second end attached to the second pivot. The linkage unit is attached to the second pivot and the third pivot and rotates about the second and third axis of rotation. The sensor unit is on a surface of the linkage unit and comprises a Hall-effect sensor located in a plane perpendicular to the third axis of rotation and located at a distance d1 from the third axis of rotation. The first magnet is: a cylindrical or cylindrical shell magnet having an axis of rotational symmetry which is perpendicular to the parallel faces thereof; or a prism-shaped magnet comprising two polygonal parallel faces and an axis of rotational symmetry which is perpendicular to said parallel faces. The direction of the magnetic moment of the first magnet is perpendicular to said axis of rotational symmetry, and the first magnet is attached to the third pivot. The third axis of rotation and the axis of rotational symmetry of said first magnet are aligned. A distance d2 between said sensor unit and said magnet, and d1 is between 0.1 mm and 50 mm and d2 is between 0.01 mm and 50 mm.