{"id":48399,"date":"2023-04-23T11:00:00","date_gmt":"2023-04-23T09:00:00","guid":{"rendered":"https:\/\/www.bikeradar.com\/?p=316625"},"modified":"2023-04-23T11:35:49","modified_gmt":"2023-04-23T09:35:49","slug":"the-ultimate-guide-to-headsets","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/cyclingplus\/rss_feed\/the-ultimate-guide-to-headsets\/","title":{"rendered":"The ultimate guide to headsets"},"content":{"rendered":"

Everything you need to know about this key bike component <\/p>

By Benedict Pfender\n \t\t<\/p>

Published: Sunday, 23 April 2023 at 12:00 am<\/p>

\n\n

The headset is a component fitted into the head tube of your bike that enables it to steer and holds your fork in place.<\/p>\n

It usually comprises \u2013 but not always \u2013 a separate component that presses into the head tube of the bike. It sits between the crown of the fork and the bottom of the headtube, and the top of the headtube and the stem.<\/p>\n

There are almost as many variants of headset as there are types of bike, and making sense of which headset your bike uses, how it works and how to buy a replacement one is not a simple task.<\/p>\n

Here\u2019s our guide to help you get to grips with the humble headset.<\/p>\n

What are the parts of a headset, and how do they work?<\/h2>\n
\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Bearings generally sit with a sliding fit in headset cups.<\/span><\/figcaption> Benedict Pfender \/ Immediate Media<\/i><\/span><\/div>\n

There are a few different types of headset available, but they all function in a similar way.<\/p>\n

The two bearings at either end of the head tube are what make things work. Traditionally, these have been held in pressed \u2018cups\u2019, but modern bikes also see bearings fitted directly into the frame.<\/p>\n

The cups (or integrated assembly) provide the interface that locates the bearings in the frame.<\/p>\n

The fork steerer slides into these bearings.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Older loose bearings rolled directly on the hardened steel race.<\/span><\/figcaption> Benedict Pfender \/ Immediate Media<\/i><\/span><\/div>\n

A crown race at the base of the steerer mates with the bottom bearing.<\/p>\n

The conical shape of the race is centred on the fork steerer. 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. A top race performs the corresponding duties for the upper bearing.<\/p>\n

Almost 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.<\/p>\n

The top bearing carries only the axial load exerted by the preload that\u2019s applied to hold the fork in place securely.<\/p>\n

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.<\/p>\n

However, describing this component as a race on modern bikes is, strictly speaking, incorrect.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
This is the upper bearing.<\/span><\/figcaption> Kaden Gardener \/ Our Media <\/i><\/span><\/div>\n

The ubiquity of cartridge bearings (sealed units that contain all the rolling elements) means it should be more correctly defined as a \u2018seat\u2019 or \u2018mating surface\u2019.<\/p>\n

Because the cartridge bearing comes as a pre-assembled unit, the crown race doesn\u2019t have to support the ball bearings, these are contained inside the bearing assembly itself.<\/p>\n

Finally, preload must be applied to the bearings to ensure everything is secured and remains in place. The general rule is that preload should be enough to prevent any rocking or movement of the steerer tube, while still allowing the fork to rotate freely.<\/p>\n

What type of headset do I have on my bike?<\/h2>\n

What is a threaded headset?<\/h3>\n
\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
You\u2019ll likely find a threaded headset on older or more traditional builds.<\/span><\/figcaption> Velo Orange<\/i><\/span><\/div>\n

These days, you\u2019re unlikely to find threaded headsets outside of budget bikes, some track and touring bikes, or on retro builds. However, given they were the standard for many years, they\u2019re still worth talking about.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
This schematic shows how a threaded headset works.<\/span><\/figcaption> Wikipedia Creative Commons Thewinch<\/strong><\/a><\/span><\/div>\n

On a threaded headset, the bearings sit in cups that are pressed into the top and bottom of the head tube. A race sits on the fork crown, completing the bearing assembly at the bottom of the head tube.<\/p>\n

The steerer tube of the fork is threaded and a threaded race is screwed into the top of the fork to snug up against the top bearing.<\/p>\n

The top race will generally incorporate a bearing cap with seals to shield the bearings from debris and the elements. Tightening this allows you to set the preload. This assembly is then secured with a locknut, holding the fork in place.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
A quill stem is held in place with an expanding bung or wedge.<\/span><\/figcaption> Jack Luke \/ Immediate Media<\/i><\/span><\/div>\n

The stem \u2013 known as a quill stem \u2013 attaches separately, sliding inside the steerer tube. It is secured by tightening the top bolt, which engages an expanding wedge at its base to clamp the stem in place.<\/p>\n

Depending 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.<\/p>\n

However, the threaded design brings with it a few complications.<\/p>\n

\u00a0<\/p>\n

The fork must be matched precisely to the head tube length of the frame \u2013 it\u2019s important that the steerer of the fork is just long enough to provide enough engagement for the threads of the locknut, without the locknut bottoming out on the top of the steerer.<\/p>\n

The adjustment of a threaded headset also requires specific spanners sized to (the large dimensions of) the threaded race and locknut \u2013 not something you would necessarily want to take with you on rides.<\/p>\n

Threaded headsets can sometimes have an annoying tendency to undo themselves due to a phenomenon known as precession<\/a>. Regular care and maintenance can combat this, but still, it can be an issue.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
On the right bike, a quill stem can give a really elegant overall look.<\/span><\/figcaption> Velo Orange<\/strong><\/a><\/span><\/div>\n

Because threaded headsets comprise multiple overlapping components, they have increased weight over modern threadless designs, which are now more commonplace.<\/p>\n

However, you\u2019ll still get a few misty-eyed romantics lamenting the loss of the elegant lines of a threaded headset. As a result of this nostalgia, threaded headsets are going through a bit of a resurgence in the custom-bike market.<\/p>\n

What is a threadless \/ A-headset?<\/h3>\n
\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
A typical external threadless headset.<\/span><\/figcaption> Benedict Pfender \/ Immediate Media<\/i><\/span><\/div>\n

The threadless headset is a much simpler and arguably superior design. It\u2019s quicker and easier to service, which can be done with standard tools \u2013 hex or Torx keys in most cases.<\/p>\n

As with the threaded headset, bearings are fitted at the top and bottom of the head tube. A crown race sits at the bottom of the steerer tube and mates with the lower bearings.<\/p>\n

But, unlike the threaded design, the fork is not captive to the headset and is only held in place by a stem clamped to the steerer extending through the head tube.<\/p>\n

\n
\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
This schematic shows how a threadless headset is put together.<\/span><\/figcaption> Wikipedia Creative Common Thewinch<\/strong><\/a><\/span><\/div>\n

The stem is clamped to the outside of the steerer tube, and its height can be adjusted with spacers.<\/p>\n

Before tightening the stem, preload must be applied through the top cap, with a bolt that \u2018pulls\u2019 on a star nut<\/a> or bung fixed inside the steerer tube.<\/p>\n

Star nuts are only really used with metal steerer tubes. The two rows of \u2018star-shaped\u2019 teeth are curved so they bend back when pressed into the steerer, but bite into place when a preload is applied, pulling against the direction of the teeth.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
A star nut on the left, and an expander on the right.<\/span><\/figcaption> Benedict Pfender \/ Immediate Media<\/i><\/span><\/div>\n

For carbon forks (with a carbon steerer), an expander (also known as a bung) is installed, which spreads the load across a wider area inside the steerer.<\/p>\n

Expanders also mitigates against crush injuries of the carbon steerer, as they provide a \u2018solid\u2019 element to support the carbon when the stem is clamped in place.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Tightening the top cap applies preload to the headset bearings.<\/span><\/figcaption> Benedict Pfender \/ Immediate Media<\/i><\/span><\/div>\n

The preload force is transmitted via the stem (and spacers), which sit slightly proud of the steerer tube at the top (around a 2\u20133mm gap is ideal), \u2018pulling\u2019 the steerer tube up, applying preload and seating the fork properly in the bearings.<\/p>\n

The conical crown race locates the steerer with respect to the lower bearing at the base of the head tube.<\/p>\n

The top bearing interfaces with a slotted conical compression ring. As preload is applied, the compression ring effectively gets wedged between the top bearing and the steerer tube, tightening around the steerer as preload is applied and the slot closes.<\/p>\n

This secures the steerer tube with respect to the top bearing. Unlike the threaded steerer, where the threaded race provides a direct connection with the steerer tube, here the compression ring is required to take up any \u2018slop\u2019 between the steerer and the bearing.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
The split compression provides the interface between steerer and top bearing.<\/span><\/figcaption> Benedict Pfender \/ Immediate Media<\/i><\/span><\/div>\n

On high-end headsets, the compression ring is often a captive element of the headset cap that sits on top of the headset to seal it from the elements. With preload applied, the stem can be tightened, clamping things in place.<\/p>\n

Once the stem has been tightened, the top cap doesn\u2019t serve any purpose. It\u2019s just there to apply the initial preload before the stem secures the whole assembly.<\/p>\n

There are a few different types of threadless headset available, but they all follow the same basic assembly principle. The differences are mainly in how the bearings are fitted into the frame.<\/p>\n

What is an external threadless headset?<\/h2>\n
\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
An external headset is the original threadless design.<\/span><\/figcaption> Jack Luke \/ Immediate Media<\/i><\/span><\/div>\n

This is the original threadless design. The bearings sit in external bearing cups, and the bearing cups are pressed into the top and bottom of the head tube.<\/p>\n

The bearings are generally a transition fit inside the headset cups. That means that while they can still be removed by hand with some force, they sit snugly inside their seat.<\/p>\n

The bearings generally have a conical interface with the cup, which helps secure and locate the bearing inside the cup when preload is applied.<\/p>\n

Some manufacturers (such as Chris King) choose to press-fit the bearings inside the headset cups.<\/p>\n

This improves the security of the bearing and prevents movement, but does mean the bearings can\u2019t (officially) be removed for servicing and have to be cleaned and serviced in situ.<\/p>\n

What is an internal \/ semi-integrated headset?<\/h2>\n
\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
A semi-integrated headset sits within the headtube.<\/span><\/figcaption> Josh Patterson \/ Immediate Media<\/i><\/span><\/div>\n

As above, the bearings sit in cups, but these, in turn, sit inside, rather than proud of, the head tube, with only a small lip protruding to locate the cup and prevent it being pressed all the way inside the head tube.<\/p>\n

In order to accommodate the bearings inside the cup, the head tube has a larger overall diameter.<\/p>\n

A side-effect of this is that larger diameter tubing can be used, resulting in increases in stiffness of the frame in this area.<\/p>\n

What is an integrated headset?<\/h2>\n
\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
An integrated headset creates a clean look (if you clean your bike).<\/span><\/figcaption> Benedict Pfender \/ Immediate Media<\/i><\/span><\/div>\n

An integrated headset does away with the bearing cups, with the bearings dropped into pre-shaped seats at either end of the head tube \u2013 the head tube takes over the duties of the bearing cups.<\/p>\n

The bearings actually sit loose within these seats \u2013 they aren\u2019t fitted with the press fit that you might expect from components, such as press-fit bottom-brackets.<\/p>\n

Instead, the head tube is bored with conical seats. When preload is applied, these angled seats result in the bearings self-aligning, as well as securing them in place, creating a rigid assembly.<\/p>\n

It has been claimed this configuration is a cost-saving measure on behalf of manufacturers. Rather than pressing a bearing cup into the frame, the bearing can simply be dropped in during assembly.<\/p>\n

It also appears to allow slightly more relaxed manufacturing tolerances, though it is critical the two bores are machined concentrically and on the same axis for good fitting of the headset.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
The bearings just drop in to preformed seats, and are held in place by the preload<\/span><\/figcaption> Benedict Pfender \/ Immediate Media<\/i><\/span><\/div>\n

The standard angle for the conical bore is 45 degrees. 36 degrees is now considered obsolete, but may occasionally be found on older frames.<\/p>\n

In some cases, the seats may be machined out square with respect to the head tube and inserts can then be pressed in with the required contact angle.<\/p>\n

Conceptually, the zero stack and integrated bearing arrangements could also be adapted to threaded headsets as well.<\/p>\n

Mixing headset standards<\/h2>\n
\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Manufacturers will often choose to mix different types of headset.<\/span><\/figcaption> Benedict Pfender \/ Immediate Media<\/i><\/span><\/div>\n

Some head tubes use a mix of different designs, for example, an external cup at the bottom and a semi-integrated design at the top.<\/p>\n

What is a crown race?<\/h2>\n
\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
The crown race supports the cycling load.<\/span><\/figcaption> Benedict Pfender \/ Immediate Media<\/i><\/span><\/div>\n

Apart from the interface with the frame, the headset must also interface with the steerer tube.<\/p>\n

Forks have traditionally been fitted with a crown race near the crown of the fork. Originally, loose ball bearings were used for the headset, and this provided a hardened and precisely machined surface for the balls to roll on.<\/p>\n

As mentioned, nowadays, with the common use of cartridge bearings, this part is strictly speaking a seat (given that the races are integral to the cartridge bearing). However, the term \u2018race\u2019 has carried over, in this case it means a surface for the bearing to mate with.<\/p>\n

Crown races are often headset specific, with many different variations of the precise dimensions and interface with the bearings. Therefore, if you are swapping a headset, you will probably need to swap the crown race on the fork.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
A split fork race is easier to install and remove.<\/span><\/figcaption> Benedict Pfender \/ Immediate Media<\/i><\/span><\/div>\n

Cartridge bearings also allow for split crown races to be used, easing installation. Because the crown race acts as a seat, it can be slotted without negative impact, allowing it to be opened up to loosen the fit when installing or removing it.<\/p>\n

The use of cartridge bearings has also allowed for the development of integrated crown races. Because the load is spread by the outer seat of the bearing (rather than hard bearing balls rolling directly on the seat), softer materials, such as carbon fibre, can be used to construct the \u2018race\u2019.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
An integrated crown race (this one isn\u2019t removable) interfaces directly with the headset bearings.<\/span><\/figcaption> Benedict Pfender \/ Immediate Media<\/i><\/span><\/div>\n

An integrated crown race is simply a steerer tube that has been shaped to mate precisely with the outer race of the headset bearing. This takes over the duties of the crown race that would have been installed before.<\/p>\n

Integrated crown races typically come in two different angles \u2013 36 or 45 degrees.<\/p>\n

What are the common steerer diameters?<\/h2>\n

The other key part to consider is the steerer diameter. The standard sizes are 1 inch, 1 1\/8 inch, 1.25 inch and 1.5 inch steerers.<\/p>\n

You may occasionally come across a 1-inch threadless steerer, but you\u2019re more likely to find a threaded steerer in this size. 1 1\/8 inch threaded steerers are, however, quite common.<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Tapered steerers are widespread on modern bikes.<\/span><\/figcaption> Benedict Pfender \/ Immediate Media<\/i><\/span><\/div>\n

Tapered steerer tubes are the most common arrangement on modern bikes. This attempts to provide the best of both worlds, with a wide crown that provides improved steering stiffness, with a tapered top section that saves a little weight. This is found on both mountain bikes and road bikes.<\/p>\n

The corresponding shape of the head tube (known as a \u2018frustum\u2019 in engineering circles) also allows frame design to be optimised, with the larger lower section providing a larger surface area to connect with the down tube.<\/p>\n

This allows designers to increase stiffness here, with the top tube kept relatively skinny to improve riding comfort and reduce weight.<\/p>\n

SHIS Standards: ZS, IS, EC. What does it all mean?<\/h2>\n
\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
It was once all so simple with only a few headset standards on the market. These days\u2026 well, it\u2019s not quite that simple.<\/span><\/figcaption> Velo Orange<\/strong><\/a><\/span><\/div>\n

There are plenty of options then.<\/p>\n

Thankfully, there is a standard of sorts for headsets to help navigate you through the array of parts, and \u2013 moreover \u2013 the names of parts on the market.<\/p>\n

If you\u2019re shopping around, you\u2019ll notice different brands have different names for the same headset type.<\/p>\n

The SHIS (Standardised Headset Identification System) describes headsets in a way that makes it easier to find what you need.<\/p>\n

The identifier starts by describing the headset type with a two letter code \u2013 \u2018EC\u2019 stands for external cup; \u2018ZS\u2019 for zero-stack\/ internal headset; and \u2018IS\u2019 for integrated headset.<\/p>\n

The number following the headset type denotes the head tube bore diameter (or bearing\/cup outer diameter). The number is given in whole millimetres, but does not always correspond exactly to the dimensions of the bore.<\/p>\n

It should be considered as a code for the different sizes, with each number uniquely identifying a head-tube diameter.<\/p>\n

SHIS for external cup (EC) headsets<\/h3>\n
<\/colgroup>
Common name<\/th>SHIS name<\/th>Bore inside diameter (mm)<\/th>Cup outside diameter (mm)<\/th><\/tr><\/thead>
1 in JIS<\/td>EC29<\/td>29.85 \u2013 29.9<\/td>30 \u2013 30.1<\/td> <\/tr>
1 in Pro<\/td>EC30<\/td>30.05 \u2013 30.1<\/td>30.2 \u2013 30.3<\/td> <\/tr>
1 in BMX<\/td>EC33<\/td>32.6 \u2013 32.7<\/td>32.8 \u2013 32.9<\/td> <\/tr>
1-1\/8 in external<\/td>EC34<\/td>33.9 \u2013 33.95<\/td>34.05 \u2013 34.15<\/td> <\/tr>
1-1\/4 in external<\/td>EC37<\/td>36.9 \u2013 36.95<\/td>37.05 \u2013 37.15<\/td> <\/tr>
1.5 in external<\/td>EC44<\/td>43.95 \u2013 44<\/td>44.1 \u2013 44.15<\/td> <\/tr>
1.5 in external<\/td>EC49<\/td>49.57 \u2013 49.61<\/td>49.7 \u2013 49.75<\/td> <\/tr>
1.5 in external<\/td>EC56<\/td>55.9 \u2013 55.95<\/td>56 \u2013 56.05<\/td> <\/tr><\/tbody><\/table><\/div>

The bore depth for an external headset should be at least 15mm.<\/p>\n

SHIS for semi-integrated\/zero-stack (ZS) headsets<\/h3>\n
<\/colgroup>
Common name<\/th>SHIS name<\/th>Bore inside diameter (mm)<\/th>Cup outside diameter (mm)<\/th><\/tr><\/thead>
1 in semi-integrated<\/td>ZS41<\/td>41.35 \u2013 41.4<\/td>41.45 \u2013 41.5<\/td> <\/tr>
1-1\/8 in semi-integrated<\/td>ZS44<\/td>43.95 \u2013 44<\/td>44.05 \u2013 44.1<\/td> <\/tr>
1-1\/2 in semi-integrated<\/td>ZS49<\/td>49.57 \u2013 49.61<\/td>49.7 – 49.75<\/td> <\/tr>
1-1\/2 in semi-integrated<\/td>ZS55<\/td>54.9 \u2013 54.95<\/td>55.05 \u2013 55.1<\/td> <\/tr>
1-1\/2 in semi-integrated<\/td>ZS56<\/td>55.9 \u2013 55.95<\/td>56.05 \u2013 56.1<\/td> <\/tr><\/tbody><\/table><\/div>

The bore depth for a zero-stack headset should be at least 12.5mm.<\/p>\n

SHIS for integrated (IS) headsets<\/h3>\n
<\/colgroup>
Common name<\/th>SHIS name<\/th>Bore inside diameter (mm)<\/th>Bearing outside diameter (mm)<\/th>Bore depth (mm)<\/th><\/tr><\/thead>
1 in IS (Cane Creek)<\/td>IS38<\/td>38.15 \u2013 38.25<\/td>38<\/td>3.1 \u2013 3.2 (top) \/ 6.9 \u2013 7 (base)<\/td> <\/tr>
1-1\/8 in IS (Cane Creek)<\/td>IS41<\/td>41.1 \u2013 41.2<\/td>41<\/td>3.1 \u2013 3.2 (top) \/ 6.9 \u2013 7 (base)<\/td> <\/tr>
1-1\/8 in Italian<\/td>IS42<\/td>41.95 \u2013 42.05<\/td>41.8<\/td>2.8 \u2013 3.0 (top) \/ 6.6 \u2013 6.8 (base)<\/td> <\/tr>
1-1\/4 in IS (lower only)<\/td>IS47<\/td>47 \u2013 47.1<\/td>47<\/td>49.1 \u2013 49.2 (base)<\/td> <\/tr>
1-3\/8 in IS (lower only)<\/td>IS49<\/td>49.10 \u2013 49.2<\/td>49<\/td>51.1 \u2013 51.15 (base)<\/td> <\/tr>
1-1\/2 in IS (lower only)<\/td>IS52<\/td>52.05 \u2013 52.15<\/td>52<\/td>7.3\u20137.5 (base)<\/td> <\/tr><\/tbody><\/table><\/div>

SHIS terminology for integrated bearing refers to a 45-degree contact angle with the head tube. 36 degrees is now considered obsolete.<\/p>\n

SHIS for the steerer<\/h3>\n
<\/colgroup>
Common name<\/th>SHIS name<\/th>Steerer diameter (mm)<\/th><\/tr><\/thead>
1 in French threaded<\/td>M25-1.0<\/td>25.0<\/td> <\/tr>
1 in threaded (English, Italian, JIS, BMX etc.)<\/td>25.4-24tpi<\/td>25.4<\/td> <\/tr>
1-1\/8 in threaded<\/td>28.6-26tpi<\/td>28.6<\/td> <\/tr>
1-1\/4 in threaded<\/td>31.8-26tpi<\/td>31.8<\/td> <\/tr>
1 in threadless<\/td>25.4<\/td>25.4<\/td> <\/tr>
1-1\/8 in threadless<\/td>28.6<\/td>28.6<\/td> <\/tr>
1-1\/4 in threadless<\/td>31.8<\/td>31.8<\/td> <\/tr>
1-1\/2 in threadless<\/td>38.1<\/td>38.1<\/td> <\/tr><\/tbody><\/table><\/div>

The dimension of the headset is further defined by codes identifying the diameter of the fork steerer at the top and bottom of the head tube.<\/p>\n

The upper section of the steerer is identified by its diameter, and in the case of threaded steerers by the thread used for that steerer.<\/p>\n

SHIS for the crown race \u2014 common crown race standards<\/h3>\n
<\/colgroup>
Common name<\/th>SHIS name<\/th>Crown seat diameter (mm)<\/th><\/tr><\/thead>
1 in Pro<\/td>26<\/td>26.43 \u2013 26.49<\/td> <\/tr>
1 in JIS<\/td>27<\/td>27.03 \u2013 27.09 <\/td> <\/tr>
1-1\/8 in<\/td>30<\/td>30.015 \u2013 30.075<\/td> <\/tr>
1-1\/4 in<\/td>33<\/td>33.03 \u2013 33.09<\/td> <\/tr>
1.5 in<\/td>40<\/td>39.79 \u2013 39.85<\/td> <\/tr><\/tbody><\/table><\/div>

The lower section is identified by the diameter of the fork crown race, which is another number code corresponding approximately to the crown race inner diameter in mm.<\/p>\n

<\/colgroup>
Common name<\/th>SHIS name<\/th><\/tr><\/thead>
1-1\/8 in Cane Creek standard<\/td>30 (36)<\/td> <\/tr>
1-1\/8 in Italian standard<\/td>30 (45)<\/td> <\/tr>
1-1\/4 in<\/td>34 (45) <\/td> <\/tr>
1-3\/8 in Cane Creek standard<\/td>37 (36)<\/td> <\/tr>
1-3\/8 in Taiwan standard<\/td>37 (45)<\/td> <\/tr>
1.5i n 36-degree<\/td>40 (36)<\/td> <\/tr>
1.5 in 45-degree<\/td>40 (45)<\/td> <\/tr><\/tbody><\/table><\/div>

All this can be combined to define the precise specification for the upper and lower bearings of the headset.The crown race angle may further be identified by an angle specified in brackets. This is particularly relevant for integrated crown races, where the angle is fixed at either 36 or 45 degrees.<\/p>\n

As an example, a traditional 1-1\/8in external threadless headset with a straight steerer would be defined as follows:<\/p>\n