I'm pretty new on this and want to buy a spare inner tube. These are my specifications of the tires:

  • Tire Size 47
  • Tires Maxxis DTR-1, 650b x 47c
  • Wheel Size 27.5
  • Presta valve

When I'm browsing, I see results like:

  • Inner Tube - 650B/27.5" - 27.5" / 1.5" / 2.4" / Presta
  • 650x28-42 Bike Inner Tube - Presta
  • 27.5" x 1-1/2 (650x35) Presta Tube

But I have no idea what the 1.5"/2.4", 1-1/2, etc. mean. Which one should I choose?

  • 1
    Does this answer your question? Is there a certain size tube for my tyres? Nov 30, 2020 at 6:34
  • I guess that 1-1/2 is a way of writing 1½ inch (same as 1.5"). Nov 30, 2020 at 13:36
  • The first rule of inch sizes in bicycle tires is that they are not same as the size of the actual tire. The second rule is that if there are two sizes that are the same number but one is written in decimals and other in fractions, they are not the same size.
    – ojs
    Dec 1, 2020 at 7:37

1 Answer 1


1.5"/2.4", 1-1/2 are the tyre width ranges the tube is compatible with. Your tyre size is indicated in mm (ETRTO standard sizing), but 47 mm is 1.85" so 1.5" / 2.4" is compatible.

The 650x28-42 is for narrower tyres. 1-1/2 (650x35) (1.5 inch, 35 mm)is likely too narrow as well, although one should check the actual lower and upper limits.

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