Bikes are made up of many different parts that come in all shapes and sizes.
This makes each bike unique and gives it certain advantages and disadvantages, but can create countless compatibility headaches. What many cyclists find tricky to understand is the bike headset types.
Every bike has a headset. Without one, you wouldn’t be able to steer!
In this article, we’re going to tell you everything you need to know about headsets by running through these topics:
- What Is A Headset On A Bike?
- How Do Bike Headsets Work?
- 4 Key Bike Headset Types
- Understanding Headset Sizing
- How To Pick The Right Headset For Your Bike
- Identifying A Headset
Let’s dive in!
What is a Headset On A Bike?
The headset is the interface between the fork and the bike’s frame. It’s what allows the fork to turn despite being attached to the frame.
In practical terms, the headset is a bearing set which sits inside the head tube of the bike (the tube that the fork and steerer tube run through at the front of the frame).
A headset consists of multiple parts, and there’s actually a lot more to a headset than you might think. Here’s what makes up a headset:
#1. Bearings
Headsets internally have multiple bearings to help give them movement. On some headset systems, they are loose, and in others, they are held in a cartridge.
#2. Races and Cups
Headset races and cups are what the bearings sit on. This gives them the freedom to move and a clear track to run on.
#3. Compression Assembly
Then we have the compression assembly. This is what sits inside the headtube and holds the headset, frame, and fork altogether.
#4. Top Cap and Spacers
The top cap sits at the top of the steerer tube, and the spacers sit around it externally on the sides. They help compress the system together alongside the compression assembly.
Credit: Michael Shields, CC BY-SA 2.5, via Wikimedia Commons.
How Do Bike Headsets Work?
A modern headset can be fairly complex, and if you have ever taken one apart, you might have found many more pieces than you thought.
They work in a very simple way, though, and understanding the process of how they work can help you put one together.
You have two sets of bearings, one at the bottom of the headtube and one at the top. These bearings sit on the races or cups. The races and cups provide a smooth surface for the bearings to roll left and right, giving you the ability to steer.
To ensure this system stays together, you have the compression assembly. This means the fork doesn’t fall out of the bottom if you were to lift the bike up. Typically you have a star nut or compression bung in the forks, which connects to the top caps and spacers on the frame.
4 Key Bike Headset Types
Bike headset types come in all shapes and sizes and, over the years, have changed greatly. Typically you get four main types of headsets. Here’s what you need to know:
#1. Threaded Headset
A threaded headset is typically found on older bikes.
You have a fork with a threaded steerer tube and use a threaded lock nut to hold it all together in place. They are very old technology and are not typically seen on modern bikes.
#2. Threadless Headset (A-Headset)
Then we have the threadless headset – also known as the “A-headset”.
These headsets use compression to pull all the bearings together. They come in internal and external versions and are one of the most common systems used for budget and mid-range bikes.
#3. Integrated Headset
Integrated headsets – unlike threaded and threadless – sit in cups built into the head tube of the frame.
This eliminates the need for headset cups which is a big advantage. The bearings sit inside the frame hence the term integrated. They are very easy to swap over and service.
#4. Semi-Integrated Headset
Semi-integrated headsets are also known as “internal” or “zero-stack” headsets.
They are similar to integrated headsets, but instead of the frame having internal cups built in, you install the cups yourself. They typically have a larger diameter than integrated headsets, which allows for wider frame tubing to offer extra stiffness at the front end of the bike.
Understanding Headset Sizing
Not only do you have a lot of different bike headset types, but you also have many different sizes.
They can be very challenging to understand, but we can make them much easier for you. Many headsets come with a code related to the Standardized Headset Identification System.
Using this system, you can make measuring your headset easy, which we will be teaching you how to do later when we put it all together.
External Cup (EC) Headset Sizing Chart
| SHIS Ref. | Bore Internal Diameter (mm) | Cup Outside Diameter (mm) |
|---|---|---|
| EC29 | 29.8 – 29.9 | 30 – 30.1 |
| EC30 | 30 – 30.1 | 30.2 – 30.3 |
| EC33 | 32.6 – 32.7 | 32.8 – 32.9 |
| EC34 | 33.9 – 33.95 | 34.05 – 34.15 |
| EC37 | 36.9 – 36.95 | 37.05 – 37.15 |
| EC44 | 43.95 – 44 | 44.1 – 44.15 |
| EC49 | 49.57 – 49.61 | 49.7 – 49.75 |
| EC56 | 55.9 – 55.95 | 56 – 56.05 |
Integrated Headset (IS) Sizing Chart
| SHIS Ref. | Bore Internal Diameter (mm) | Cup Outside Diameter (mm) |
|---|---|---|
| IS38 | 28.15 – 38.25 | 38 |
| IS41 | 41.1 – 41.2 | 41 |
| IS42 | 41.95 – 42.05 | 41.8 |
| IS47 | 47 – 47.1 | 47 |
| IS49 | 49.10 – 49.2 | 49 |
| IS52 | 52.05 – 52.15 | 52 |
Semi-Integrated Headset Sizing Chart
| SHIS Ref. | Bore Internal Diameter (mm) | Cup Outside Diameter (mm) |
|---|---|---|
| ZS41 | 41.35 – 41.4 | 41.45 – 41.5 |
| ZS44 | 43.95 – 44 | 44.05 – 44.1 |
| ZS49 | 49.57 – 49.61 | 49.7 – 49.75 |
| ZS55 | 54.9 – 54.95 | 55.05 – 55.1 |
| ZS56 | 55.9 – 55.95 | 56.05 – 56.1 |
Steerer Tube Headset Sizing Chart
| SHIS Ref. | Steerer Tube Diameter (mm) | Standard Name |
|---|---|---|
| M25 – 1.0 | 25 | 1” Threaded (FR) |
| 25.4 – 24TPI | 25.4 | 1” Threaded |
| 28.6 – 26TPI | 28.6 | 1” – ⅛” Threaded |
| 31.8 – 26TPI | 31.8 | 1” – ¼” Threaded |
| 25.4 | 25.4 | 1” Threadless |
| 28.6 | 28.6 | 1” – ⅛” Threadless |
| 31.8 | 31.8 | 1” – ¼” Threadless |
| 38.1 | 38.1 | 1” – ½” Threadless |
Crown Race Headset Sizing Chart
| SHIS Ref. | Crown Race Diameter (mm) | Standard Name |
|---|---|---|
| 26 | 26.43 – 26.49 | 1” PRO |
| 27 | 27.03 – 27.09 | 1” JIS |
| 30 | 30.015 – 30.075 | 1” – ⅛” |
| 33 | 33.03 – 33.09 | 1” – ¼” |
| 40 | 39.79 – 39.85 | 1” – 1.5” |
How To Find The Correct Headset For Your Bike
As you can see, many different headsets are available and come in many different sizes. It can be very challenging to understand what you need for your bike.
Here are three methods that are going to make it easier.
#1. Find The Headset Code
The first and easiest way to find the correct headset for your bike is to find the code on the headset you are replacing.
On many headsets, you will have a small code, typically the manufacturer’s reference code or size. This will make it easy to find online.
Unfortunately, not all headsets have this code – and if you don’t already have a headset to use as a reference in a frame you’re building up, this method isn’t going to work for you.
#2. Check With The Manufacturer
The next thing you can do is to look for the details of your bike or frame on the manufacturer’s website.
This is a very easy way to find the correct information, and many bike frame brands will even recommend certain headsets with part codes to match.
#3. Measure The Frame and steerer tube
If neither of the above options are possible, the third option is to measure it for yourself.
This might seem daunting, but we’ll be going into more detail in the next section.
Identifying A Headset
We recommend using vernier calipers for maximum accuracy.
For the measurements you take, you can compare them with the charts above to find the corresponding SHIS reference or Standard Name.
#1. Upper Bearing Type
First, identify the bearing type. This will either be Internal Cup (IS), External Cup (EC), and Semi-Integrated/Zero Stack (ZS).
#2. Upper Bearing Cup Size
To get this measurement, you will need to get your vernier calipers and measure from one side of the bearing cup to the other side.
#3. Fork Steerer Size
Here you need to measure from one side of the steer tube to the other. Ensure not to measure around, as this is a common mistake many make.
#4. Lower Bearing Type
Just like you had to with the upper bearing now, you need to identify the lower bearing. Avoid assuming it will be the same as the upper, as many headsets are mixed.
#5. Lower Bearing Cup Size
Just like you did with the upper bearing cup size, do the same with the lower bearing. Do not be surprised if it is larger than the upper bearing cup, as these often differ.
#6. Crown Race Size
To measure the crown race size go to the lower part of the fork steerer tube. Here you need to measure across, not around. This is the crown race size.
