My omafiets (classic Dutch granny bike) has a flat tyre and I am looking for a replacement.

It currently fits a 42-635 measure, but I am struggling to find it locally and/or the outside tyre alone costs 25€. I was wondering if I could fit a 40-635 instead? (So just 2mm tighter) - seems easier to find and cheaper.

Thanks for your help.

  • Wider tires usually means more comfortable because you can run them at lower pressure. Obviously, 2mm won't make a huge difference but worth keeping in mind. Also 25 EUR doesn't seem unreasonably expensive. Cheaper isn't always better, especially if you go from a reputable brand to some no name rubber. There's a surprising amount of technical know-how that goes into making good tires (even on an Omafiets, higher puncture resistance and lower rolling resistance will make your life better). May 7, 2023 at 13:34
  • Thanks a lot for your comment, appreciate it! I have an electric bike and only keep this omafiets when I go somewhere I prefer not to go with the electric bike to. For the value of the bike and the usage, doesn’t make much sense for me to spend 25-30€ on a Continental tyre (only one I could find). Different story if it was my primary bike as you said.
    – Giuseppe
    May 7, 2023 at 14:33
  • Thank you for using the ETRTO numbers and not anything else - that makes comparisons so much easier.
    – Criggie
    May 7, 2023 at 19:23

1 Answer 1


The 635 in the size is the rim diameter. So, both tires fit the same rim, and 40 may or may not be slightly narrower because the width measurement is never exact.

  • And yes, this kind of bike will accept a slightly narrower tire, most people riding them will not even know the details of tire sizes.
    – Willeke
    May 7, 2023 at 12:03
  • ...which is not a great thing, since there are two so-called 28" sizes and this is less common of them. It's good that the OP asked instead of buying the wrong one first.
    – ojs
    May 7, 2023 at 12:08
  • Thanks all for your feedback. I will indeed stick to 635 as the rim diameter cannot be changed - was more wondering about the 2mm less width wise. Will go for 40-635. Thanks again!
    – Giuseppe
    May 7, 2023 at 13:09

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