I'm really confused what inner tube size I need to buy for the tyres I have. Is anyone able to help me understand what is written on the tyre and what to look for? tyre wall 40/100-622 33b moped m/c

  • Out of curiosity, what's the brand and model of the tire? May 15, 2018 at 21:40
  • Vee Rubber Speedster, wire bead, reflective strip, 700x40c May 15, 2018 at 21:50
  • @BenHorsburgh - Tubes are sold as 700c x (range of numbers). Buy a tube that has range of numbers contain 40, e.g. 700c x 38-42 or something. (The position of the c may be different; go to your local bike shop and they should have you sorted out in about a minute, since you also need to know the valve type, which is likely presta)
    – Batman
    May 15, 2018 at 21:52
  • I’m really confused about the size as well. ISO/ETRTO should read <tire width>-<bead seat diameter>, eg. 40-622. The /100 doesn’t make any sense. Can you simply measure the width?
    – Michael
    May 16, 2018 at 8:16

1 Answer 1


622 is the "official" ISO actual diameter of the rim, which is commonly called a 700c for road bikes, 29" for moutain bikes.

Ask for a 29er tube as big as you can get it. e.g. 29x2 29x2.5 Because 29ers are mountain bikes, they have bigger tubes.

If you get a 700cx40 tube, it will be much smaller, and in my experience, fail prematurely.

As a matter of interest I measured a tube that was rated for 700c 30-40mm. At 30mm, it stretches of 38%, at 40mm 84%. That tube is probably OK at 30mm. When you get 700C tubes for fatter tyres, you only get the overstretched end of the range.

  • 2
    The tube needs to be sized correctly to the tire. Too small will definitely cause problems, but so will a tube that is too large. May 16, 2018 at 0:08
  • 1
    Too small is not that much of an issue.
    – Batman
    May 16, 2018 at 0:14
  • @Batman It is in my experience, hence my suggestion. Tubes are narrower than they were, for the same tyre size, and they now get pinholes and splits when almost brand new. So far, using larger tubes seems to be working for me.
    – Henry Crun
    May 16, 2018 at 0:34

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