Headset (bicycle part)

Many frame and fork manufacturers are now building their parts around a steerer tube with a diameter of 28.6 mm (1+1⁄8 in).

The larger diameter of the head tube and headset gives added stiffness to the steering portion of the bicycle.

If the headset has a lower stack height than the frame and fork, spacers are added to make up the difference.

There are a few different types of headset distinguishable by the way the bearings are held in place (with a lock nut or with a clamping stem), or by where they are located (inside or outside the head tube).

This process assures that no material is lost and the steerer would not be weakened as with a die or lathe cutting.

Under the internal design, the races and cones are embedded into the head tube, creating a tidy, streamlined appearance.

In the image shown of the 2016 Brodie Quantum's steering assembly, the lock nut is hidden from view by a plastic cover.

Headsets of this type are often referred to by the Dia-Compe (now Cane Creek) registered trademark "Aheadset",[2][3] and are manufactured under license.

The adjustment must be made such that there is no play in the bearings, but allow the fork to turn smoothly without binding or excessive friction.

In the threadless headset system, the spacers are important in placing the stem and preload bolt in the correct position on the steerer tube.

Cutting the steerer tube to its minimum length prevents switching to a taller stem or to a headset cups with a higher stack height.

In addition, many riders who may have less flexibility than a seasoned racer may wish to gain more height on the handlebars, reducing the saddle-to-handlebar drop and providing a more upright and comfortable riding position.

If an owner simply wishes to replace the headset with one having a slightly larger stack height, it may be possible for a bike shop or framebuilder to mill or re-face the head tube to gain an extra 1-2 mm of stack height without having to replace the fork.

The headset cartridge bearings therefore sit somewhat loosely in the headtube of the bicycle (as opposed to being press fit).

Prominent standards in internal headsets include Chris King's InSet and Cane Creek's ZeroStack.

Headsets on bicycles, particularly those without fenders, are exposed to water and grit thrown off by the front tire, which causes rust and rapid wear.

Better headsets use rubber lip seals or "O" rings (dirt skirt) to try to keep water out, with varying degrees of success.

External Neoprene bands with a Velcro fastening are available to wrap and protect the lower race, and are removable for cleaning.

Some cyclists remove the fork and reassemble with a section of old inner tube over the lower race, which performs the same function, albeit with less convenience.

On bicycles ridden only in dry conditions and/or with fenders, the normal failure mode is a progressive notchiness in the steering, described as "indexing" in the bicycle world, caused by pitting of the races or false brinelling, although the term stems from a misunderstanding of the cause; true brinelling is caused merely by pressing the ball axially into the race, and it is almost impossible to replicate this damage even by striking the fork crown repeatedly with a hammer.

This misaligns the bearings and causes fretting, a small amplitude, large stress movement which tears metal from the races at the points where the balls rest.

[11] The solution is to have a 45 degree interface in the headset where this flexing movement can be accommodated, preserving the relative alignment of the races and allowing the ball bearings to take pure axial and rotational loads.