However, the threaded design brings with it a few complications. It is secured by tightening the top bolt, which engages an expanding wedge at its base to clamp the stem in place.ĭepending on the length of the quill, you can adjust the height of the stem easily by sliding it further up or down inside the steerer and fixing it in the correct position.

The stem – known as a quill stem – attaches separately, sliding inside the steerer tube. However, describing this component as a race on modern bikes is, strictly speaking, incorrect.Ī quill stem is held in place with an expanding bung or wedge. Incidentally, the interface between bearing and fork is called the race (crown race and top race) because it originally acted as the raceway, with the bearing balls in the headset rolling directly on it. The top bearing carries only the axial load exerted by the preload that’s applied to hold the fork in place securely.

A top race performs the corresponding duties for the upper bearing.Īlmost all of the axial load experienced by the fork during riding will be carried by the lower bearing, because this is effectively sitting on top of the fork. This means it is self-centring on the bearing and, when preload is applied, the angled shape ensures it supports both axial and lateral loads. The conical shape of the race is centred on the fork steerer. Benedict Pfender / Immediate MediaĪ crown race at the base of the steerer mates with the bottom bearing. Older loose bearings rolled directly on the hardened steel race.

Forged carbon fiber bike