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Determining the size of a bicycle wheel can quickly turn into an ordeal. Let's face it, the current measurement system, with its three standards, is a mess. What do the numbers on a bicycle tire mean? How do you interpret them? How do you choose the right size from the different types of bike wheels without getting it wrong? It's time to give this imbroglio a whirl. Decipher it with our guide to bike wheel sizes.
The useful standards for defining a bike wheel size
To understand how the system used to measure bicycle wheel sizes works, we need to look at the standards in place. These are the basis for the numbers noted on the sidewalls of bicycle tires. Did you think they were indescribable hieroglyphics from ancient times? Nope! Let's take a closer look.
The French standard in millimeters
The tricolor standard is based on three criteria:
the outer diameter of the tire, expressed in mm;
the width of the inflated tire, expressed in mm;
the inner diameter of the rim, expressed as a letter (A, B, C or D).
A handy clarification: the outer diameter encompasses the total height of the tire, i.e., the distance between the bead wire and the tread is included in the measurement.
Here is an example of a wheel size under the French standard: 700 x 25C. This inscription corresponds to the following dimensions: 700 mm outer diameter, 25 mm width.
To not complicate things, the meaning of the letters (thus the internal diameter of the tire) depends on the outer diameter:
| Wheel 650 | Wheel 700 | |
|---|---|---|
| A | 590 mm | 642 mm |
| B | 584 mm | 635 mm |
| C | 571 mm | 622 mm |
| D | 78-85 kg | 587 mm |
The French standard is generally used to refer to road and gravel bike wheel sizes.
The English standard in inches
The English standard takes into account two criteria:
the outer diameter of the tire, expressed in inches;
the width of the tire, expressed in inches.
No letters, then, in the Anglo-Saxon measurement system.
Here is an example of a wheel size under the British standard: 27.5 inches x 2.35, for a tire outer diameter equivalent to 27.5 inches and a tire width of 2.35 inches.
There may be a third element in the listing, like this: 26 x 1 1/8 x 1 1/2. In this case, the second number is the tire height and the last number is the width.
The English standard is the reference for defining the size of ATV, EAB, mountain bike and cyclo wheels.
The ETRTO International Standard
To bring some semblance of consistency to this pretty mess, there is fortunately the ETRTO (European Tire and Rim Technical Organization) standard. This international ISO 5775 standard makes some harmonization of standards possible thanks to a correspondence table.
The ETRTO standard calculates the dimensions of a bicycle tire based on two criteria:
the width of the tire, expressed in mm;
the inner diameter of the rim, expressed in mm.
Here's an example of the ETRTO notation: 26 x 622, for a tire that's 26 mm wide and has an inner diameter of 622 mm.
Considering the inside diameter of the rim, not the outside diameter of the tire, allows for a more accurate measurement for better tire and rim fitment.
This is the universal standard you should use when choosing your bike wheel size, for both road and mountain bike use.
The rim height
Our size guide also looks at rim height for road cycling:
Low profile wheels: rim height under 30mm for mountain use, with lots of climbing;
Medium profile wheels: rim height between 30mm and 50mm for aerodynamics;
High profile wheel: rim height over 50mm for time trial or sprinting on flat terrain.
Keep in mind that the choice of his wheels depends primarily on the size of his bike frame and tire clearance.
Tire width
Before choosing a tire, you should check the width of your rims. Indeed, a narrow rim will not accommodate a tire that is too wide and vice versa. Once again, it is the ETRTO standard that allows you to establish a reliable correspondence between tire width and rim width.
In road cycling, tires come mostly in 23C, 25C and 28C. A 25C tire provides an ideal compromise for regular cyclists.
The most common bike wheel sizes
The popular 700C: for road and gravel bike enthusiasts. The most common letter for this size is C, equivalent to an internal diameter of 622 mm.
28-inch wheels: the name of the tires mounted on trekking bikes and city bikes for bike tourers.
29-inch wheels: a wider tire dedicated to mountain bike enthusiasts for riding off the beaten path.
Now you've become an expert in bike wheel size! After the theory, let's get practical: observe the marking on your bike tires and determine the exact size of your wheels according to the three standards. It's up to you!"
