(Last updated on March 27th, 2023)
Cycling is a great sport. It lets you get into nature, meet new friends, and is an amazing way to stay in shape. There’s a lot to learn about bikes, and I get asked many questions about the parts that bring them together.
A common question I do get asked is, “How are bike stems measured?” Stems can be quite confusing to understand, and they greatly affect the position you ride on the bike. In this article, I am going to be speaking about:
What is a Bike Stem?
A bike stem is a component on a bike that attaches the fork steerer tube to the handlebars. It allows you to steer and change the rider’s position on the bike. A stem is a vital part of the bike, and without it just wouldn’t work.
Stems come in many different shapes and sizes. Older stems are called Quill Stems, and more modern stems are called Stems. A Quill stem goes into the fork steerer through the top, and a normal stem goes around the tube.
Why Does the Size of a Bike Stem Matter?
The length of a bike stem surprisingly makes a huge difference to a bike and how the rider will feel on the bike. Here’s what you need to know:
Handling
The length of a stem drastically changes how a bike handles, and professional cyclists swap out stems for certain races for the ability they need or want.
A shorter stem makes a bike much more agile and allows you to turn quickly. This is great for off-road riding and is perfect for very technical terrain. You will often see mountain bikes on short stems as small as 50mm. This can make the handling feel erratic and too responsive, which isn’t ideal at high speeds.
A longer stem will make the handling feel less agile and is great for riding at very high speeds because it makes the bike much easier to control. Road bikes often have long stems up to 120mm as they are much better at higher speeds, making the handling less responsive as you turn the bike.
Comfort
A stem does a lot to the comfort of the rider. When you get a bike fit, the fitter generally keeps many stems of all different angles and lengths. This is to achieve the perfect fit and get the most comfort for the rider.
A stem that gives the rider a more upright riding position will offer much more comfort, and it will feel much more relaxed riding in that position. A longer stem that stretches you out forward will feel much more aggressive and offer less comfort but more performance.
Aerodynamics
When it comes to going fast, aerodynamics plays a big part, and a bike’s stem can completely change how a rider is positioned aerodynamically. A longer, lower stem will improve aerodynamics hugely, but it will also put the rider in a less comfortable position.
A shorter, higher stem will offer less performance as fast as aerodynamics go, but it offers better comfort and control. It depends on the riding you are doing to which is more beneficial.
Looks
Many riders use different stems to change the look of their bikes. A lower stem which puts the rider in a much more aerodynamic position, makes your bike look like a pros bike. Although it looks very cool, it generally isn’t at all comfortable.
How are Bike Stems Measured?
Bike stems are measured in two different ways. You have length and angle. When buying a stem, these are the two measurements you will want to ensure you get right, or it could make riding uncomfortable.
The stem length is from the fork steerer tube and goes out to the handlebars at the front. The angle is measured from the center of the stem to what angle it goes upwards or downwards towards the handlebars.
Different Types of Bike Stems
Like many bike parts, bike stems come in different shapes and sizes. Knowing the different types of bike stems you might find on the market is important. Here is an example of a few different types.
1. Modern Stem
A modern bike stem will look like this. It attaches to the fork steer tube and wraps around it before being clamped with two bolts on the rear. On the front, you have four bolts that grip the handlebars. These are typically universal, and you will see these on mountain bikes, road bikes, and even hybrid bikes.
2. Quill Stem
A quill stem is often referred to as a classic stem. These are not often seen on modern bikes and are typically only used on classic bikes. They fit inside the steerer tube instead of wrapping around it like a modern stem. They are much smaller and generally are designed for thinner classic handlebars. These are not interchangeable with modern stems.
3. Adjustable Stem
Adjustable stems are a replacement for a modern stem. They offer the ability to adjust the angle for the rider. This means you can make the bike more comfortable or more aggressive. It’s a great way to adjust the bike for different riding, but only really seen on hybrid bikes more than anywhere else.
4. Suspension Stem
Finally, we have the suspension stem. This looks like a modern stem but internally has suspension. This means it takes the edge off rough roads when going over bumps. They are excellent for gravel riding and give your bike good ability on the trails.
How to Measure a Bike Stem Our Guide
Now for the fun bit, measuring a bike stem. Here’s our guide on how are bike stems measured. There are a few different ways I will speak about it. You will require the following:
- A Tape Measure or Vernier Caliper
- A Protractor
- A Ruler
- Allen Keys (Optional for removal)
Method One: Check For Markings
The first and easiest way to measure a stem is to look for the markings. In general, many companies will put exactly what the stem is on the stem itself. You will need to look for a measurement in mm for length. Then you might also find a degree which will be the angle.
Method Two: Check the Specification of the Bike
If you have a standard from a factory bike, you can use the specification sheet to find out what stem you have. I recommend going to the manufacturer’s website and looking at the specification sheet; it will tell you everything you need to know.
You will need to look under the stem specification, which will tell you the length in mm and the degree measurement too. It’s worth checking that your stem looks the same so you can ensure it’s the right one.
It’s not rare for cyclists to use different stems on bikes as they are not difficult to change and completely change how a bike feels and the level of comfort you get when riding.
Method Three: Measure it Yourself
The final way to determine the stem measurement is to measure it yourself. It’s not challenging to measure a stem. Here’s the process I recommend going through:
Step One (Optional): Remove the Stem
This first step is optional but can make measuring a stem much easier. It is possible to do it while the stem is on the bike, but it is a bit more challenging. So if you want, use the Allen keys to remove the stem from the bike. You will need to remove the handlebars to do this.
Step Two: Measure the Length
The next step is to measure the length of the stem. This is pretty easy, and you will only require a measuring tape. You need to take your tape measure and put it in the center of the part of the stem which houses the fork steerer tube.
It has to sit in the middle of the circle, where stems are measured. Then you must take the measuring tape to the center of the stem where the handlebars sit. Imagine you are putting it in the middle of the handlebars.
Take this measurement, and it will be the length of the stem. The measurement should be in multiples of ten, for example, 90mm, 100mm, 110mm, or even 120mm. If it isn’t, you must double-check your measurements. Here’s a video on how to measure stem length.
Step Three: Measure the Angle
Measuring the angle of the stem is more challenging, and it does help if the stem is off the bike. You need to take the protractor out and situate it in the center of the stem fork steerer holder from the side so the angles point toward the stem’s end where the handlebars sit.
Then I recommend taking the ruler and putting it across to where the center of the handlebars sit, keeping it completely vertical. Measure the degrees where the ruler crosses. Typically you will find the angle between negative 10 and positive 17 degrees. If it’s out of this range, measure again.
Step Four: Measure the Handlebar Width
Finally, you need to measure the handlebar width. The best way to do this is with the vernier caliper or the measuring tape. Where the stem houses the handlebar, you will want to measure the width of the hole. This will typically be 31.8mm on most modern bikes, but some are smaller, and it’s worth looking out for smaller sizes on older bikes.
A Final Note
Changing the stem on your bike can make a huge difference to the comfort of your riding. It can give you a more relaxed riding position for those long days out in the saddle or make you aggressive and aerodynamic for racing.
I highly recommend trying different stems to see what works for you. It’s important if you are going to try different stems to be able to measure them so you know what you’re putting on.
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Frequently Asked Questions
The only person who can officially tell you that is a qualified bike fitter. As we are all different shapes and sizes, it’s important to seek advice or try some and see what works. It’s not as simple as bike size charts or wheel size charts.
MTB or mountain bike stems are measured like road bikes and hybrid bike stems. They are generally much smaller in length to give the MTB agility and control.
A 0-degree stem is flat and will offer a more aggressive riding position compared to a 6-degree stem which is more upright and offers a more relaxed riding position.
It’s the right size for a road or gravel bike, but generally, 100mm is only good if it suits the rider it’s made for. Stems change depending on different bike sizes too.
Generally, a short stem brings the rider more upright, making it more comfortable. There are also many other ways to increase comfort, such as better shoes.
I’m Robbie Ferri, a writer from Norfolk in the UK. I love cycling, the gym, and have a huge passion for sharing my stories and knowledge to anyone with the time to read them. My main passion is cycling. I started eight years ago. In that time I have broken world records, cycled all over the world in Ultra Bikepacking races, and am lucky enough to have enjoyed some incredible times on two wheels with some incredible people. I have also worked in a bike shop and with some of the industries leading brands, not just promoting products but designing them too.
Under it all I am just someone very passionate about exploration and living a healthy lifestyle. Everything I do I put 100% into it and feel that life is for living. Never should you have a dull day.
