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i have bought a new bicycle recently, i have noticed that it's tire size is not traditional and i can't find anywhere tube with appropriate size (27 inch), can i use tube which fit with 27.5 inch tire?

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    Does this answer your question? I have 27 inch wheels and need new inner tubes what size can I use
    – Weiwen Ng
    Commented May 4 at 10:40
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    That question was written before 27.5 inch became common. In 2020s it could be worth pointing out that 27.5 inch tire is quite a bit smaller than 27 inch and inch sizes are even more illogical than before.
    – ojs
    Commented May 4 at 10:44
  • Ok i understood, thank you very much for a very detailed answer :-)
    – Greta
    Commented May 5 at 14:27

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Look on the side-wall of your tyre for a number in the format xx-yyy or possibly reversed to be yyy-xx. This is the ETRTO naming standard for tyres.

I guess yours is 48-584 as an example; substitute your own values from the sidewall.

The 2 digit number will be the approximate width in millimetres when installed and inflated. This can vary a little and still work on your bike. So the tyre is 48mm wide though you could use a tyre width from 42 through to 56, at a guess.

Just be sure to get the same valve style as your current tube, be it Presta or Schrader (aka car tyre)

The 3 digit number is the Bead Seat Diameter and represents the distance straight across your rim from edge to edge, through the axle. This number is also in millimetres and must be the same else it won't clip into your rim at the bead.

For a tube there's a bit more tolerance because they're stretchy. Look at the side of the tube's box and it will state several ranges, and probably a lot of different formats including inch-style.

You can disregard inches because the ETRTO format is accurate, whereas inches have been around too long and there are multiple confusing usages in tyres.

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  • Just out of curiosity, why would 27" be 584 instead of 630?
    – ojs
    Commented May 5 at 10:57
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    @ojs I picked 584mm because its the 27.5" size aka 650b. That value is used as an example here. 48mm is a middle of the range width, and OP can subsitute their own values. If OP had said 29" then I might have used 622 in the example. 630 would be quite unlikely on a new bike today.
    – Criggie ♦
    Commented May 5 at 11:40
  • Did you read the question? It is pretty explicit about the 27" size, and asking if a different size 27.5 would fit.
    – ojs
    Commented May 5 at 12:52
  • @ojs Certainly did. And I answered it too. I could have used 21-216 as an example, or 99-686
    – Criggie ♦
    Commented May 5 at 19:09

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