An aerodynamic assembly for bike handlebars, includes two distinct extension devices (4a, 4b), each of the two extension devices (4a, 4b) having: a first armrest-forming part (5a, 5b), able to be fastened on a transverse bar of a bike handlebars (1) while extending longitudinally forwards and including a longitudinal extension (6a, 6b) forming a free end portion. An upper surface of the first part with its longitudinal extension forming a receiving surface for a forearm part of a cyclist. A second extension-forming part (8a, 8b), able to be fastened, in a removable manner and in the extension of the first part (5a, 5b), to the free end portion, the second extension-forming part (8a, 8b) being able to slide longitudinally relative to said longitudinal extension (6a, 6b) so as to allow an adjustment of a distance separating a free end of the second extension-forming part (8a, 8b) from the first armrest-forming part (5a, 5b).