What tire width fits my rim?

Some measurements in inches, others in millimeters, still others a combination of numbers and capital letters. But all you really want to know is which of our tires you need for your rim. If this simple question has ever tied your brain in knots, you've come to the right place. In this article, we'll sort out the chaos for you.

Why the different size specifications for bicycle tires?

First, the good news: the problem is not with you. Rather, the question marks in your head are pointing to a problem that the bicycle industry has been grappling with for several decades. Like all industries, it is a historically grown entity, where regional customs and national standards initially prevailed. This became increasingly impractical as production and trade globalized. So, organizations were created to standardize these norms. For our topic, the ETRTO is the authoritative (and literally measuring) institution. The acronym stands for European Tyre and Rim Technical Organisation. It was founded in 1964 and set itself the task of taming the resulting proliferation within Europe. Unfortunately, this hasn't fully worked, and different specifications are still in circulation. But if you know a few things about it, it won't cause you any difficulties in the future.

ETRTO standard, inch designation and French sizes

Let's take a closer look at the tire specifications, for example. Usually, there is a place on every tire where a specification like this is printed:

25-622 [28 x 1.00 / 700 x 25C]

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

Now for the specifications in square brackets. The first — 28 x 1.00 — is the inch designation or inch dimension. From this, you can infer the approximate tire outer diameter (in this case 28 inches) and also the tire width (1.00). This specification comes from the Anglo-American region, where measurements are taken in inches ("Zoll" here is simply the German translation). Because mountain biking is very heavily influenced by America, you will still primarily find inch specifications there today, while the road bike sector tends to measure in millimeters.

The third specification is a special approach taken by the major cycling nation France, which is why we speak of "French sizes." The first number, 700 in the example, stands for the tire outer diameter, as in the English designation. Therefore, it differs from the ETRTO standard, although both are given in millimeters. The second number (25 in the example), as you have probably already noticed, matches the ETRTO specification. Here, too, it denotes the tire width.

One slightly complicated aspect of the French standard is that it also includes a specification for the tire inner diameter depending on the tire outer diameter — encoded by the letters A, B, and C. For an outer diameter of 700 mm (as in the case of our example tire), C means an inner diameter of 622 mm. For a different outer diameter, it would have a different meaning. Fortunately, manufacturers usually specify the ETRTO standard in addition to the French sizes, so this should not cause you any difficulties.

Rim: What needs to fit?

It's best to stick to the ETRTO standard regarding our initial problem of which tires you can use with your rims. Because it provides you with exactly the information that must match your rim.

The Rim Nominal Diameter

More precisely: First, the inner diameter of the tire must match the so-called rim shoulder diameter or rim nominal diameter. The rim shoulder is the part of the rim bed on which the tire rests. Therefore, if you want to determine your rim nominal diameter, you cannot simply measure from one outer edge of the rim to the opposite one with a tape measure; instead, you have to deduct 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's a high probability that the rim's nominal diameter is 622 mm. This is the standard size. If you're unsure, take a close look at your rim. Usually, there's a small sticker or a tiny imprint somewhere with the exact measurements.

It is important to note: The rim nominal diameter must exactly match the tire inner diameter. Otherwise, the tire will not sit correctly. With tire width, however, you have a bit more leeway. And that brings us to the next point.

The rim inner width

To know which tire width fits your rim, you need the rim inner width as the second dimension for the rim. This refers to the inner distance between the rim flanges. It therefore does not correspond to the actual rim width, which is measured from outer edge to outer edge. Nevertheless, the term "rim width" is often used figuratively when the inner width is actually meant. Even in specialist literature.

And there's another potential for confusion. A typical size specification on a rim could look like this:

622 x 15C

The first number is the rim nominal diameter (here, the standard size 622 mm). The second number refers to the inner width. It is also given in millimeters. However, the C here 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 nominal diameter match, as can be easily seen. But what about the width? Our table will help you here (and of course with all your own current and future tires and rims). The first column lists the inner widths of the rims. In the second column, you see the range of tire widths you can choose from. As a special service, we have provided this in both millimeters and inches. With this, nothing should go wrong with your tire choice. If you like, feel free to browse our offers for tires and wheels!

(Source: Schwalbe, retrieved on 14.08.2025)