Bike stems are one of the most important components of your bicycle since they impact your performance as well as your comfort. Typically, they come in various sizes and lengths to cater to different cyclists but to select one for yourself, you need to know how to measure one.
Here are the steps to measure a bike stem:
- Stabilize the bike on a stand.
- Now measure the length/extension of the stem.
- After that, measure the angle a/b.
- Next, measure the rise.
- Finally, measure the height.
To help you in further understanding, I will discuss everything you need to know, from how to measure a bike stem to how to select the best-suited one for yourself.
But before we dive into that, let’s look at the basics first.
The Structure of a Bike Stem
Here are the three structural dimensions you should know to measure a bike stem:
- Stem Length
- Stem Rise
- Stem Diameter
#1 Stem Length
The length of a bike stem is the most important factor of a stem. The stem length impacts the bike’s responsiveness, fit and ride and directly affects the rider’s handling.
A short stem is likely to have faster handling and more responsiveness, while a longer stem will be much slower and would be less responsive.
#2 Stem Rise
The stem rise is the angle of a stem that’s relative to the fork’s steerer tube and ranges from about 6 degrees to 20 degrees.
Stems come in different amounts of rise. Most stems that are fitted off-the-shelf bikes tend to have a moderate rise.
However, stems with an extreme amount of rise can provide the option to adjust the position of your handlebar significantly.
Bike stems are flippable, so you can angle them down to achieve a lower aerodynamic position or upwards to put the handlebars in a more upright position. But this all depends upon the amount of rise the stem has.
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#3 Stem Diameter
There are two diameters of the stem, steerer tube diameter and handlebar diameter. Both these come in various designs and sizes.
Steerer tubes have a diameter of about 1-⅛ inch and sometimes even 1-¼ inches.
On the other hand, handlebars are designed in various diameters from 31.8 mm to 25.4 mm.
How To Measure a Bike Stem?
It’s simple to measure your bike stem; you only need a measurement tape and a bike stand.
Here is a step-by-step guide that you can follow to measure your bike stem with ease.
#1 Stabilize the Bike On a Stand
To measure the bike stem correctly, you have to put your bike on a bike stand to stabilize it while you do the measuring.
You can put the bike against a wall for support or upside down as long as it remains stable while doing your job.
#2 Measure the Length/Extension
A bike’s stem extension is basically the measurement in determining the bike stem’s length. Instead of measuring from one end of the stem to the other, this measurement is done from the center of the steering bore to the center of the handlebar clamp.
First, take your measuring tape and place it onto the center of the steering bore and pull the tape till you reach the center of the handle clamp, and record that measurement.
A bike’s stem length usually runs in about 10 mm increments or starts somewhere at 70 mm to 140 mm.
After this, you need to measure the reach by using tape. Put the tape on the head tube’s center and pull it to the bottom bracket.
If you have a stem rise, the reach measurement is the horizontal projection of your bike’s stem.
#3 Measure the Angle A/B
The angles are divided into two parts, angle A and angle B.
Angle A is the angle between your bike’s stem and an imaginary horizontal line. If your stem goes straight and perpendicular from your steering column, the angle is zero. But if your bike stem has a slope upwards then an angle is here.
Angle B is known as the full angle between the steering column and your bike stem. It’s also referred to as the stem angle in biking terminology. Therefore, if a bike has a stem that sticks straight out perpendicular from the steering column, then angle A would be 90 degrees.
However, if the bike’s stem has a rise, then you can add angle A to 90 degrees, and the sum would be angle B. Simply put, it is:
Angle B = Angle A + 90 degrees.
#4 Measure the Rise
The rise is the effective height gained from the function of the bike’s stem angle and length.
Take your measuring tape and measure from the center of the bike’s handlebar clamp to an imaginary horizontal line that extends perpendicularly from the central contact of the extension and the vertical part of the stem.
#5 Measure the Height
The height is basically the overall length of the vertical portion of the bike’s stem.
It’s simple to measure the height since you only need to measure the small vertical portion of your bike stem.
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Bike Stem Types
Bike stem has two types, and they both differ so bike riders can find the most compatible and suitable bike for themselves.
The two types of bike stems are called quill bike stems and threadless bike stems. The type of bike that you want must be compatible with your bike’s headset and fork.
Here is how these two bike stem types differ in their characteristics;
Threadless Bike Stems
A threadless bike stem usually clamps around the steering column of your bike and is held in place with the help of tight pinch bolts. The right part is clamped on the steering column, while the left is clamped around the bike handlebars.
If you are looking to change your bike stem, it is recommended to look for a modern-day 4-bolt design since it is stronger and stiffer than the old 2-bolt face plate.
Standard threadless steerers come in various sizes such as 1-inch, 1-1/8-inch, and 1-1/2-inch.
Quill Bike Stems
A quill stem is normally attached to the inside of the steering column through compression by inserting a bike stem and tightening the bolt on the top that pulls the stem upwards.
Threaded quill steerers mostly come in sizes between one inch to 1-1/8-inch diameter.
They are structurally very different from the threadless stem; therefore, they are also measured differently.
The measurements are taken perpendicularly from the middle of the bike’s steerer tube to the middle of the bike’s handlebar clamp.
How to Choose the Right Bike Stem?
Choosing the right bike stem is crucial if you don’t want to have poor handling on your bike.
Here are some factors that you should consider before choosing a bike stem for yourself.
The length of the bike stem is one of the most important things to consider since it can affect the bike’s responsiveness; a long stem is likely to cause a slower bike response than a short stem which reacts more quickly.
This is why many bike racers prefer a shorter stem, and long-distance cyclists prefer a longer stem.
Choosing the correct stem length not only affects your bike’s responsiveness but also impacts your comfort.
You need to be aware of your bike’s stem inseam length and upper body measurements.
This is because your own body can also affect your suitable stem length. Your height is important to determine the correct bike stem length. If your upper body is long and the inseam is short, a short bike stem is more suited for your height.
But if you have a long inseam and a short upper body, then a long bike stem is ideal for you. Usually, people have a well-proportioned body that allows them to select the bike stem based on the bike type.
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Apart from the stem length, stem reach is crucial in selecting the most compatible bike stem for yourself. A bike without enough reach can cause you discomfort and body aches.
The stem length alters the distance that you have to reach the handlebars. If you ride often and don’t feel discomfort, it’s probably a good fit for you.
But if you feel like you’re stretching forward and it’s causing strains or cramps in your back and pain in the shoulders and neck, these are clear indications that you need to replace your stem for a shorter or longer one.
A bar clamp diameter is the diameter of the bike’s handlebar, which the stem clamps onto. If your bike is new, it will have a handlebar clamp diameter of about 31.8 mm, while an old one might have 25.4 mm.
To see what diameter you have, take out your measuring tape and measure your bar diameter carefully. The bar diameter is important because it directly relates to the stiffness of the handlebars.
If you prefer getting a stuff handlebar, then the 35 mm bar diameter is ideal.
However, it is pretty hard to find handlebars or stems of that diameter because, apart from one or two companies in the market, many of them are still working on launching that size.
When choosing a bike stem, the material is also very important. The majority of bike stems are made from aluminum alloy.
These bike stems are durable, lightweight, and super affordable. Kids’ bikes and some cheap bikes are made from steel.
In recent times, bike stems made from carbon fiber are preferred over aluminum, even if they are a bit expensive. These have a bit more weight than aluminum. These are a popular choice for cyclists nowadays because they are stiffer and look good.
When selecting the ideal stem for your bike, you need to make sure that you select one which offers you to ride the bike in an optimum riding position.
Aim for a position where you have to slightly bend your elbows to allow your arms to move easily as the front wheel tracks the surface of the ground.
Don’t aim for a position where your arms are all stretched out straight because that indicates that the stem is too long for you.
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To ensure you get the optimum position, go for a test drive or get a professional bike fit. A good rule of thumb for selecting the correct stem length is to sit on the bike with your hands placed on top of the hoods and look down to the front hub.
If the handlebars completely hide the front hub, then the stem length is correct for you, but if you can see the hub in front of the bike’s handlebars, then the stem length is too short.
When choosing the right bike stem, you need to see the amount of rise and drop it provides.
Most of the standard bike handlebar’s rise amount is between 6 degrees to 20 degrees.
The rise or drop of the handlebars can help you select your suitable riding position. If you prefer a high front end, you can select a handlebar with more rise.
However, if you prefer a lower front end and your riding position requires you to lean forward, then handlebars with little to no rise are recommended.
Frame Size-Specific Stems
Many bike manufacturing companies try to fit bike stems across the size range, so bikes with shorter stems have small bike frames and long bike stems have large frames.
This sizing approach makes it easier for people to get the correct stem length, provided that you choose the right frame size.
The typical stem length size on road bikes goes from 80 to 140 mm, with 100 mm and 110 mm as the most common or preferred sizes amongst them.
However, if you still think you can’t find your suitable stem size, you can always get a custom one with your desired frame length.
There are two clamps on a stem: a handlebar clamp at the front and a fork steerer at the back.
Most of the stems are designed to have a 4-bolt design for the handlebar clamp, replacing the old standard 2-bolt face plate design.
The fork steerer clamp has more designs, such as a 2 bolt design, some DH stems have a big single bolt and some XC stems have a wedge design with the bolt situated in the body of the stem in the front of the fork steerer.
When selecting a stem, pick one that does not have rear clamp bolt heads that stick out a bit too far out because these can potentially hurt your knees while riding or if you crash.
Look for a stem that has cowled or rounded-off bolt-head designs.
How Does the Bike’s Stem Length Affect Handling?
The stems work with the other components of the bike, and they directly affect the sitting position of the cyclist, which affects the handling. A longer stem will be slow to steer, while a shorter stem will be snappier.
The stem length can determine the responsiveness of the bike, such as the longer a bike stem, the slower a bike will respond, whereas the shorter a stem, the quicker a bike will respond.
By now, the art of measuring a bike stem must seem pretty simple. These are the simplest ways to measure your bike stems in the comfort of your garage.
Remember, the right bike stem can do wonders to your riding performance. So go ahead and get your compatible bike stem using this guide.