When it comes to bicycle headsets, they tend to be overlooked on many bikes, the bike headset actually provides an essential function. They will be used every day, it is the part that lets you steer your bike and will also hold the fork in place.
What does a headset do?
The headset is the interface between the fork and the bike frame, by holding it securely in place, it will help you to rotate and steer. This will need lateral stiffness so that it can withstand riding loads, especially when it comes to cornering, braking and potholes. It’s important that it is also rotationally free when it comes to steering.
What’s included in a headset?
There are a number of different types of headsets available, but they work and function in a similar way. The two bearings at either end of the head tube are what makes the process work, more traditionally they will have been held up in pressed cups, however modern bikes will also have the bearings fitted onto the frame. The cups or integrated assembly will make sure that the interface can locate the bearings in the frame.
The fork steerer will slide into the bearings but will need fittings to be held securely, a crown race at the base of the steerer will work with the bottom bearing. The conical shape of the race will be centred on the fork steerer, this means that it is self centring on the bearing and when the load is applied. The shape will make sure that it supports both the axial and lateral loads, the top race will support the upper bearings.
All of the axial loads from the fork will be carried by the lower bearing, this will be effectively sitting at the top of the fork. This top bearing will provide the axial load exertion by the preload that will be applied to help hold the fork in place securely.
The interface between the bearing and the fork will be called the race, this is because it acts as the raceway with the bearing balls in the headset. When it comes to this component on modern bikes, it will be different. The cartridge bearings, sealed units that include all of the rolling elements. As the cartridge is a pre-assembled unit, the crown race won’t have to support the ball bearings, they will be contained inside the bearing assembly.
The preload should be applied to the bearings and will make sure that everything is secured and stays in place, the general rule is that the preload should be enough to stop any rocking or movements of the steerer tube, while the fork can still rotate freely.
What type of headset is on my bike?
When it comes to threaded headsets, the older or more traditional bike will have them, there are a range of options available, including NTN bearings. These days you tend to not see threaded headsets outside of budget bikes as well as track and touring bikes or on retro builds.
On a threaded headset, the bearings will sit in cups that will be pressed to the top or bottom of the head tube. The race will sit on the fork crown and complete the bearing assembly at the bottom of the head tube.
The steerer tube of the fork will be threaded and a threaded race will be screwed to the top of the fork against the top bearing. The top race will include a bearing cap with deals that will protect the bearings from debris and the elements. By tightening this, you can set up the preload, the assembly will then be secured with a locknut and hold the fork in place.
The stem which is also known as a quill stem, will attach separately and slide inside the steerer tube, it will be secured by tightening the top bolt and this will engage when the wedge is expanding at the base, it will then clamp in place.
Depending on the length of the quill you will be able to adjust the height of the stem easily and then slide it further up or down inside the steerer, then you can fix it in the right position.
This threaded design is known for having a number of complications, the fork will need to be matched precisely to the head tube length of the frame, its then important that the fork steerer is long enough to offer engagement for the threads of the locknut.
The adjustment of the threaded headset will also need specific spanners that are sized to it, the threaded race and locknut isn’t something that you would want to take on rides.
Threaded headsets sometimes come with an annoying tendency that will undo themselves due to precision, regular care and maintenance will combat this.