The headset includes upper and lower rolling bearings (8, 9) housed inside the head tube so as to allow relative rotation of the steering tube, and clamping elements (18, 21) for axially clamping the lower and upper bearings (8, 9) against, respectively, a lower end and an upper end of the head tube. The axial-clamping elements include a threaded sleeve slipped over the steering tube. This sleeve is secured to the steering tube by connecting elements including a pin extending through two diametrically opposed holes in the threaded sleeve and through two diametrically opposed holes provided in the steering tube. The sleeve collaborates with a tapped annular cap slipped over the steering tube so as to force the upper bearing downward as the annular cap is screwed onto the sleeve.