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Say you are riding on 622-19 rims. This means that each rim's bead diameter is 622 mm, and the distance between the two beads on each rim is 19 mm.

ETRTO stands for European Tire and Rim Technical Organization. But that does not mean that if you are riding, say, 25 mm tyres, you can refer to your tyres as 622-25; does it? Can the smaller/second number refer to the tyre width, so that you would say "I installed 622-25 tyres on 622-19 rims")?

Also, I see 37-622 in addition to the more common 622-37. Which one is correct?

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    From the name it seems that it apply to tires. Do you consider tyres to be something different?
    – Vladimir F Героям слава
    Apr 8 at 15:15
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    @VladimirFГероямслава I'm in Canada. We're perpetually confused. We spell "colour" (officially, at least) and "tyre" (the latter making sense, to distinguish it from the verb "to tire"), but we also say "sidewalk" and use 8.5"x11" paper.
    – Sam7919
    Apr 8 at 15:19

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Yes!

We can refer to the tyre size and the rim size using millimetres by the ETRTO system.

Note that the rim diameter comes first in it's designation, while for the tyre we put the width first. So we would write 37-622 for the tyre (it's not correct the other way, or more common)

You would say that you had installed your 25-622 tyre on the 622-19 rim. Presumably they are typical crochet types and you could include the C to give 622-19C rim.

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  • Spot-checking, your answer seems exactly right. For tyres the correct order is 25-622, and for rims it's 622-19.
    – Sam7919
    Apr 9 at 16:06
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The actual standards are behind a paywall but ETRTO https://www.etrto.org/ publishes standards about both rims and tyres for many kinds of vehicles, including bicycles. Some recommendations can be downloaded, but they do not contain these kinds of numbers.

Schwalbe uses the order 37-622 for the tyres, but I cannot get to the actual standard document. The same order is used for ISO 5775 which originates from the ETRTO standard.

Regarding your "I installed 622-25 tyres on 622-19 rims": Why not, the rim and the tyre are two different objects and both have their sizing according to the standard.

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  • "I installed 622-25 tyres on 622-19 rims" has redundancy - anyone doing tyres knows 622 applies to both tyre and rim, so ""I installed 622-25 tyres on 19mm rims" would work fine.
    – Criggie ♦
    Apr 8 at 21:32
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    Or more colloquially, "I installed 25mm tyres on my 19mm rims" would be how someone might say it. The BSD isn't as important cos almost all road bikes have the one size, and if you're a MTB then again width is more important.
    – Criggie ♦
    Apr 8 at 21:34

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