Everything you need to know about bike tires and wheel sizes

Why is it so difficult to get new tires for your bike? For those who have never looked into it, it might seem like every manufacturer uses a new system and that there isn't a single standard. That's not far from the truth.

ISO size? ETRTO? French? 700C? 650B? 27" - It all seems hopeless. But don't despair: You have questions, we have answers.

Tire Size Descriptions

To demystify some of the secrets of tire sizing, we should understand the difference between perceived size and actual size. Perceived size is like ordering a "medium" milkshake. It gives you an idea of the size, relatively speaking, but doesn't tell you how much a medium milkshake contains.

Actual size, we call it ISO, is given by two numbers: The width of the tire when fully inflated, and the diameter of the tire's bead. ISO is measured in millimeters (mm). Here's an example:

32-622 - This tire has a width of 32mm and a bead diameter of 622mm.

What is a bead?

The bead is the part of the tire that is in contact with the rim. It is a wire integrated into the tire that holds the tire in place.

Do it yourself.

Not too long ago, when countries and continents kept to themselves, it was common to create one's own standards. This meant that those who produced bicycles and bicycle parts invented their own ways of describing measurements and meanings.

For example, the French described their tires with approximate sizes, 700C is one such measurement, and a glimpse into the history of bicycle tires. Similar to the ISO system, 700 is a number used to describe the diameter of the tire, in millimeters, but it is by no means exact.

In fact, there are 700A, 700B, and 700C measurements, where the letter indicates the width of the tire and A is the widest and C is the narrowest... But don't worry about it.

The ISO System (!)

At some point, the International Standards Organization decided it was time for a globalized system for measuring bicycle tires.

Originally, the ISO system was invented by the European Tire and Rim Technical Organization (ETRTO), which is why it's called ISO in some places, and ETRTO in others... But it's the same thing. Then we can argue about what is correct to say.

ISO is: The width of the tire, and the diameter of the tire's bead, measured in millimeters.

Let's say you find a tire with the number 25-622 written on the sidewall.

This tire has an ISO size of 25-622, which corresponds to a French-sized tire: 700C x 25.

How can 622 and 700C be the same?

As mentioned above, the "622" number in the ISO system refers to the diameter of the tire's bead, while "700" is a size that refers to perceived size.

What about inches?

Inches are another way to measure tire sizes, and more common for tires intended for mountain bikes and modern gravel bikes that take fat tires. A typical measurement might look like this:

27.5 x 1.50

This tire has an ISO size of:

40-584

Here is a small overview of common tire sizes in this country:

An example

In our shop, you can find the correct size by using a filter or by reading the product description. Let's say you find this tire in the shop:

Maxxis Re-Fuse Dual MaxShield TR 28

The title says 28.

28 = 700C = 29, and is most often "ISO 622". Also in this case.

Good to know:

• 29" and 28" are actually the same size.
• 29" is most often used for tires intended for mountain bikes and new gravel bikes/hybrid bikes. Because they are usually too wide for rims/bikes that need 700C tires.

If you are replacing old tires, it is important that you find the size of your old tires (written on the tire) and match them with these specifications.

Obscure Sizes

Once in a while, we see a size that looks something like this: 26 x 1 5⁄8 x 1 3⁄8. This is still a tire measured in inches, but here the height of the tire is included in the specifications. In other words: outer diameter x tire height x tire width. If you have a tire like this, and you are going to replace it, focus on the first and last numbers: 26 x 1 3/8.

Advanced

If you're still with us, give yourself a pat on the back. We know it's hard!

Sometimes you want to try wider or narrower tires. There are a couple of things to keep in mind when hunting for tires:

Which tire width fits my rims?

Which tire width fits my bike?

If you want wider or narrower tires, you need to choose a tire with a higher/lower number for the width measurement.

In addition, you need to know what type of tire is intended for your rims. This is also usually written on the rim, or in the product information (most common).

A wheel, or a rim, usually comes with product information where you will find, among other things, a "Tire Compatibility Chart". Here you can find out how narrow or how wide tires will fit this rim.

If you want to know what tire width fits your bike (frame), you need to look at the specifications for the respective model. This is usually given as a maximum width, maximum tire width. This is largely about how wide the tires can be without hitting the bike frame. You want the wheel to spin freely, without touching the frame.

Do you have questions? Comments? Write them in the comment field.