What tire width fits my rim?

Some specifications are given in inches, others in millimeters, and still others as a combination of a number and a capital letter. All you really want to know is which of our tires you need for your rim. If this seemingly simple question has ever left you scratching your head, you've come to the right place. In this article, we'll sort out the confusion for you.

Why are there different size specifications for bicycle tires?

First, the good news: The problem isn't you. Rather, your confusion touches on an issue that the bicycle industry has been wrestling with for several decades. Like all industries, it has evolved historically, with regional practices and national standards initially prevailing. This became increasingly impractical as production and trade globalized. Organizations were therefore established to standardize these norms. For our topic, ETRTO is the relevant institution (and one that literally defines the relevant dimensions). The abbreviation stands for European Tyre and Rim Technical Organisation. It was founded in 1964 and set itself the task of curbing the proliferation of different standards that had developed within Europe. Unfortunately, it hasn't completely succeeded, and different specifications are still in circulation. But if you know a few things about them, they won't cause you any difficulties in the future.

ETRTO standard, inch designation, and French sizes

Let's take a closer look at the specifications using a tire as an example. Normally, every tire has a marking printed on it that looks something like this:

25-622 [28 x 1,00 / 700 x 25C]

The first specification is the ETRTO standard. It consists of the tire width (the first number) and the tire inner diameter (the second number), both in millimeters. The tire in the example is therefore 25 mm wide and has a diameter of 622 mm at its inner edge.

Now for the specifications in square brackets. The first - 28 x 1,00 - is the inch designation, or inch sizing. It indicates the approximate tire outer diameter (28 inches in this case) and also the tire width (1,00). This specification comes from the Anglo-American region, where measurements are taken in inches ("Zoll" is simply the German translation here). Because mountain biking has been strongly influenced by the United States, inch specifications are still predominantly used there today, while the road cycling sector tends to measure in millimeters.

The third specification is a special system used by France, one of the major cycling nations, which is why it is referred to as "French sizes." As in the English designation, the first number, 700 in the example, refers to the tire's outer diameter. This is why it differs from the ETRTO standard, even though both are given in millimeters. As you have probably already noticed, the second number (25 in the example) matches the ETRTO specification. Here too, it indicates the tire width.

One slightly complicated aspect of the French standard is that it also includes a specification for the tire's inner diameter in relation to its outer diameter - encoded by the letters A, B, and C. With an outer diameter of 700 mm (as in our example tire), C indicates an inner diameter of 622 mm. With a different outer diameter, it would have a different meaning. Fortunately, manufacturers generally provide the ETRTO standard in addition to the French sizes, so this should not cause you any difficulties.

Rim: What needs to match?

It is best to follow the ETRTO standard for our original question as well: which tires can you ride with your rims? It provides exactly the specifications that need to match your rim.

The rim diameter

More precisely: First, the inner diameter of the tire must match the so-called rim shoulder diameter or rim diameter. The rim shoulder is the part of the rim bed on which the tire rests. Therefore, if you want to determine your rim diameter, you cannot simply measure from one outer edge of the rim to the opposite edge with a measuring stick; instead, you need to subtract a few millimeters or estimate where the rim shoulder is located.

However, if you ride a road bike, mountain bike, gravel bike, or trekking bike, there is a good chance that the rim diameter is 622 mm. This is the standard size. If you are unsure, take a close look at your rim. There is usually a small sticker somewhere or a tiny marking with the exact dimensions.

It is important to note that the rim diameter must match the tire inner diameter exactly. Otherwise, the tire will not seat correctly. With tire width, on the other hand, you have a little more flexibility. And that brings us to the next point.

The internal rim width

To know which tire width fits your rim, you need the second rim dimension: the internal rim width or inside width. This refers to the distance between the inside edges of the rim flanges. It therefore does not correspond to the actual rim width, which is measured from outer edge to outer edge. In a figurative sense, people often still refer to "rim width" when they actually mean internal width. This is even the case in technical literature.

There is a second potential source of confusion. A typical size specification on a rim might look like this:

622 x 15C

The first number is the rim diameter (the standard size of 622 mm here). The second number refers to the internal width. It is also given in millimeters. However, the C has nothing to do with the French size; it simply stands for "Clincher."

Rim width and tire width: The table

And now for the million-dollar question: Would our example tire (25-622 [28 x 1,00 / 700 x 25C]) fit our example rim (622 x 15C)?

The inner diameter and rim diameter match, as you can easily see. But what about the width? This is where our table helps (and, of course, it also helps with all your own current and future tires and rims). The first column lists the internal rim widths. In the second column, you can see the range of tire widths you can choose from. As a special service, we have provided the information both in millimeters and inches. Choosing the right tire should now be completely straightforward. If you like, take a look at our selection of tires and wheelsets!

(Source: Schwalbe, accessed on 14.08.2025)