By Brad Quartuccio

Of all the bearings on a bicycle, the headset is likely the least appreciated yet arguably has the most effect on actual ride quality. The headset refers to the bearing assembly that permits the fork to rotate within the frame, and is a fairly simple apparatus albeit one with a few variations to consider. Don’t get me wrong, hub and bottom bracket bearings very much influence the ride, but few things can drive a rider as batty as a loose headset. Pull up a chair and adjust your headset.

Anatomy
No matter the specific variety, headsets share a common design principle of two bearings and the surfaces that they rotate upon. From the fork on up, there is the crown race, the bearing surface that is pressed on the fork, just atop the crown. The lower bearing is sandwiched between this and the lower head race with the upper head race, another bearing, and the adjustable race at the top of the headtube. This adjustable race is referred to as such because in one form or another it floats atop the top bearing and dictates the load placed on the bearing and how tight/loose the headset is. The bearings themselves may be either loose balls or sealed cartridges which have become more common in recent years.

The difference in exactly how the adjustable race adjusts and is secured is the difference between traditional threaded headsets and relatively newer threadless headsets that came about in the late nineties and have become the dominant design on bicycles since. It is easy to differentiate the two –threaded headsets have an adjustable cup with wrench flats along with a locknut of roughly the same size, while a threadless headset does not have any wrench surface on the adjustable cup. The former system uses a threaded steerer tube and requires a quill style stem. One can thus infer that a threadless system fits onto a smooth, unthreaded steerer.

Either variety is available in a few different sizes, with the overwhelming majority of bikes having either a 1” threaded or 1 1/8” threadless headset (measurement refers to outside diameter of steerer tube), with newer bikes tending towards the latter. Other sizes are out there, but as time goes on becoming harder to source parts for. (continued)