Road Bike Stem Standards and How to Choose

Posted at: May 16, 2022

The stem is an unassuming part, but actually has a significant impact on ride comfort and speed. In this issue, we summarize road bike stem standards and how to select one.

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There are three points to consider when choosing a stem

Stem Standards

First, check what standard stem is available for your road bike. There are two standards to keep in mind when choosing a stem.

  1. column diameter
  2. clamp diameter

The column diameter is the diameter of the fork column, and is generally 28.6mm (1-1/8"), which is called “oversize” on modern road bikes. You can check the specs on the road bike manufacturer’s website or actually measure it with a measuring tool. When measuring, do so with the spacers removed.

The clamp diameter should match the diameter of the handlebars you wish to install. In the past, 28.6mm was the most common diameter, but nowadays 31.8mm is the most common. If the crank diameter does not match the handlebar diameter, the stem cannot be fixed. Here, you can look at the description of the handlebar currently installed, or you can measure it yourself since it is a bare part.

On higher grade road bikes, there are models that run the outer cable through the stem, but in those cases, the manufacturer’s genuine product is often used.

Stem Size

There are two sizes of stems for road bikes as follows

  1. length
  2. angle

Length, as the name implies, is the length of the stem and is used to adjust how far (or close) the handlebars should be positioned. The shorter the stem, the closer the handlebars are to the rider and the more upright the posture, and the longer the stem, the farther the handlebars are to the rider and the deeper the forward lean.

Angle is a factor that determines the height of the handlebars. The deeper the angle, the more extreme the handlebars rise and fall, so we dare to say “upright” and “deepen the forward lean.”

How good the angle is depends on how angled the fork of the road bike you are using is. For the past few years, the standard angle for road bikes has been horizontal to the ground.

Stems can often be flipped up and down, so if you choose a shallow-angled stem, you can use it “up for upright until you get used to it, and down for deeper forward lean once you get used to it.

Stem Material

The last thing to check is the stem material. Steel, aluminum, and carbon are the three major materials used here, with carbon stems being the most common in higher-end road bike models. Since the stem is a weight-bearing part, it is best to choose a material that is strong.

When choosing a carbon stem, be sure to select one from a major manufacturer such as Shimano or Deda. If you install a cheap carbon stem and it breaks while riding, it will be a serious accident.

Can stem replacement save weight?

Since it can be done with just an Allen key, stem replacement is an easy road bike customization that even beginners can do, so entry-level road bike users often use it as a way to reduce weight. However, unless the current stem is extremely heavy, it is not a cost-effective weight reduction.

A weight reduction of a few dozen grams or so is hardly noticeable, so there is almost no need to replace the stem for the sake of weight reduction.

Customize your stem to fit your position!

The main purpose of replacing the stem is to optimize your position. Even just knowing the distance to the handlebars and the height of the handlebars will change your position considerably, which will greatly affect the comfort and speed of your rides.

Since changing a stem is a customization that changes your position, we recommend changing it gradually rather than suddenly changing to a stem with a completely different angle and length.

You may have to purchase multiple stems to find the one that fits you best, but an ill-fitting position will make you more tired, so replace the stem as if you were fine-tuning it.

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