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Everything you need to know about bicycle tire dimensions

The different units of measurement for bicycle tires

The three units of measurement used in bicycle tires are the Anglo-Saxon expressed in inches, the French and the ETRTO, both expressed in millimeters .

The Anglo-Saxon unit of measurement: the inch

The inch is an Anglo-Saxon unit of measurement commonly used to designate the dimensions of MTB, BMX and children's bicycle tires. Its format is type XX x X,XX, par example XNUMX x XNUMX, which corresponds to:

â€“ outside diameter of the tire in inches;

â€“ tire section in inches. The symbol " is the contracted form of this unit of measure. Thus it is par possible example of writing XNUMXâ€³ instead of XNUMX inches.

The Anglo-Saxon unit of measurement corresponds to the external diameter of the tire, that is to say the one that includes the height of the sidewalls of the tire; it includes the distance between the rim and the tread.

This diameter is greater than the external diameter of the rim.

This unit of measurement is not regulated and the dimensions may therefore vary from one brand to another. It is therefore not the most reliable. A MTB tire with the dimension XNUMX x XNUMX of a certain brand may therefore turn out to be narrower than a tire XNUMX x XNUMX of another brand.

The French unit of measurement: the millimeter

The French unit of measurement is commonly used to refer to the sizes of road bike tires and city bike tires. It is expressed in the format XXX x XXX, par example XNUMX x XNUMXC, which corresponds to:

â€“ outer diameter of the tire in millimetres.

â€“ tire section; the letter C is an indication of the rim diameter.

The French measurement, expressed in millimeters, takes into account the outer diameter of the tire. This diameter is therefore greater than the diameter of the rim.

This unit of measurement is also not regulated. It may vary from brand to brand and is therefore not the most reliable. A XNUMX x XNUMX road bike tire of one brand may be narrower than a XNUMX x XNUMX race tire of another brand.

The European unit of measurement ETRTO, expressed in millimeters

The ETRTO unit of measurement is expressed in millimetres. This is a unit standardized at European level and which is recognized throughout the world for tire dimensions. The standard is governed par the European Tires and Rim Technical Organization, hence the acronym ETRTO. Its format is XX-XXX type, par example XNUMX-XNUMX, which refers to:

â€“ the section of the tire in millimetres.

â€“ the internal diameter of the tire in millimetres.

The ETRTO unit of measurement is the reference for the choice of any type of tire but it is particularly useful for finding and choosing tires of particular sizes, such as tires for bicycles child or certain urban tires.

The ETRTO diameter corresponds to the inside diameter of the tire as well as the outside diameter of the rim on which it is mounted.

How to read the size of a bicycle tire?

Knowing how to read the size of a tire on your bike without making a mistake is quite simple when you know where to look. Tire sizing information is written on the sidewall. The ETRTO is generally found there first and in parentheses, followed by the Anglo-Saxon measurement for mountain bike tires and/or the French measurement for road bike tires and city bike tires.

It is then possible to buy a new tire with the same indications or to find a tire that will be compatible. It is recommended in this case to refer to a table of correspondences, which using the ETRTO of your current tire, allows you to find the other dimensions that will go on the rim. If the tire is too old or damaged and the information is no longer readable, you will have to take the measurement yourself.

What are the most common bicycle tire sizes?

Not all bikes have the same tire and wheel size. Depending on their use, the size of bicycle tires varies. These sizes, although framed par standards can be misleading. Different dimensions can be given for the same tire diameter.

If one is looking for a XNUMX inch mountain bike tire, they will all have the same outside diameter, but the inside diameter may vary between brands and models as with shoes. So a XNUMX-inch tire can have an ETRTO internal diameter of XNUMXmm, XNUMX, XNUMX or even XNUMX mm. This inside diameter of the tire corresponds to the outside diameter of the rim. Two â€“ tires can therefore have the same outer diameter with a different inner diameter.

How do you know if a tire is compatible with a rim?

When changing tyres, it is essential to choose the right diameter but also the right width. Indeed the rims can accommodate a fork of limited section. To know the tire widths and the size correspondences between the rims and the bicycle tires, it is recommended to rely on the ETRTO code of the wheel. It is readable on the side of it and gives us the information on the internal width and the diameter of this rim.

You still have to be careful not to do anything wrong:

- A tire that is too thin on a rim that is too wide will tend to come off the rim and puncture more regularly due to pinching. Par example, your rim is XNUMXmm wide and the tire width is XNUMXmm, this one will come off the rim. Indeed, if your rim is XNUMXmm wide, it will be compatible with tires from XNUMXmm wide up to XNUMXmm. The rim and the tire must have the same internal diameter but several tires of different widths may be suitable for the same rim.

- A wide tire on a rim that is too thin leads to poor handling and will be dangerous.

- A tire can be sealed when fitted in tubeless. There are conversion kits.

- The size of the bicycle wheel also influences the inertia and therefore the handling of your bicycle. Note that a road tire with fine characteristics will be more difficult to handle for a wheel size of XNUMX inches.

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