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STEERING and WHEELS: Headsets: Introduction



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A headset allows the bike to be steered. The headset must be properly adjusted to allow smooth, safe steering and to prolong its life. The bearings and bearing surfaces need regular inspection and lubrication, and anything that is worn must be replaced at once.

How they work

The main function of the headset is to enable the rider to change the direction of the front wheel under any conditions. There are two types of headsets, threaded and threadless, and both hold the front fork securely in the head tube, while simultaneously allowing the fork to turn freely.

The headset rotates on bearings, which are held in place by cups, one above the head tube, the other below. For the forks to turn freely, these two cups press on the bearings just enough to prevent any play in the part of the fork known as the steerer tube. The way this pressure (also known as load) is achieved varies between the threaded and threadless headsets.

Right: COMPONENTS OF A THREADLESS HEADSET

The stem cap bolt at the top of a threadless headset screws into a star washer below. Some types of threadless headsets contain a wedge instead of a star washer. When the bolt is turned with an Allen key, it pushes the stem and spacer down onto the bearings in the top and bottom cups, and pulls up the steerer tube. The bottom cup covers the bearings that sit on the fork crown race at the top of the fork crown. As a result, sufficient load is placed on both bearings to enable the front fork to turn freely but without play.

  • Stem cap bolt: Pulls the steerer tube upward
  • Top cup: Loads the hearings
  • Bottom cup: Loads the bearings
  • Star washer: Grips the steerer tube
  • Stem: Links handlebar and headset
  • Spacer: Sits on top of the bearings
  • Top bearings: Allow the steerer tube to turn in the headset
  • Steerer tube: Connects the fork to the headset
  • Bottom hearings: Allow the fork to turn
  • Fork crown: Turns the fork
COMPONENTS OF A THREADLESS HEADSET

Right: COMPONENTS OF A THREADED HEADSET

Screwing the top cup down the thread of the steerer places a load on the top bearings to the point where the forks turn freely but without play. The cup, and consequently the front fork, is then locked in place by a lockring that also screws down the threaded steerer. The stem is attached to the headset by tightening the stem’s expander bolt, which pulls up a wedge and jams the stem’s quill inside the threaded steerer.

  • Stem: Links the handlebar and headset
  • Quill: Fits inside the threaded steerer
  • Top cup: Loads the bearings
  • Threaded steerer: Connects the headset to the fork
  • Lockring: Locks the top cup in place
  • Top bearings: Allow the steerer to turn in the headset
  • Wedge: Jams the quill in the steerer
  • Bottom bearings: Allow the fork to turn
  • Expander bolt: Draws up the wedge
COMPONENTS OF A THREADED HEADSET

Better, more-effective Steering

A headset allows the rider to steer the front wheel effectively and confidently. The handlebar, which is connected to the steerer tube by the stem, turns the fork and the front wheel.

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