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I'm from a place where finding a standardized size for tyres bigger than 26 inches is mostly a hassle, to say the least..

But sadly (or not) I have a bike that I've been riding for a while now and have used it enough to wear out the tyres. The stock tyres on the bike were 700×35c. The rims on the bike are, as I mentioned above, 21-622 ETRTO. Now, the tyres that are bigger than 26' that are somewhat widely available around here and are ETRTO 635mm tyres. The confusion looms because, well, both of them are referred to as 28' tyres by more than just a handful of people..

It's simply used for commute on roads I won't particularly describe as best, and I avoid most bad potholes, if that helps.

So, if I'm unable to find 700c or 622mm tyres, it is safe for me to be using the 40-635 tyres without changing the whole wheel? I mean, I can probably find a tire that has a smaller width but a smaller diameter tyre seems to be hard to find around here..

Sim
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    It might work, but there is a serious probability that the new tire would pop off the rim. And I seriously find it hard to believe that you can't find 700C (xx-622) tires, as that is one of the most common sizes in use for road bikes. – Daniel R Hicks Sep 15 '20 at 12:13
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    Does this answer your question? How are tire sizes measured? – ojs Sep 15 '20 at 12:19
  • I've read the thread you're suggesting, ojs, but I still didn't understand whether I could put on a 635mm Tyre on a 622 mm rim, I was of the belief that "just" 15 mm worth difference isn't much, just a 2.5% worth difference and it won't be much of a problem if I try to put on the bigger tyre on.. – Sim Sep 15 '20 at 12:28
  • @Daniel R Hicks, I come from a place where bicycles are looked at as a poor man's mode of transport and most people don't even know that there are specific bikes for specific purposes, let alone understand the tyre size standards! Bikes for them are categorised as "normal" and "geared" ; "normal" and "racing"... You get the drift. – Sim Sep 15 '20 at 12:35
  • 15mm isn't much when compared to 622, but look at how much the tire overlaps the rim. You'd be cutting the overlap in half, maybe more. – Daniel R Hicks Sep 15 '20 at 12:56
  • Yeah, I checked that after @Argenti Apparatus pointed it out – Sim Sep 15 '20 at 13:05
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    "28 inch" is a horrid meaningless size. the ETRTO number is a confusion-free way of describing a tyre size, so don't feel bad to think of those riders as "old-fashioned" and take their words and advice with salt. Also, you have internet/web access, and there are plenty of web-based stores that will ship you stuff. Supporting the LBS is one thing, but not carrying common sizes makes them a poor LBS. – Criggie Sep 15 '20 at 19:11
  • My limited understanding is that there are some countries where 700c (622) tires (and wheels!) are uncommon or almost nonexistent. Of course these days you can import anything from anywhere in the world, but when you're 100km from home and need a new tube, tire or even wheel, the LBS might have nothing for you. Once I tried to put a 27" (630) tube into a 622 tire, as the nearest shop with 700c (622) tubes was 45km away. It was too large to fit. So much for availability. I expect that if you try to put a 635 tire into a 622 wheel it will be too large and just pop off, or not go on at all. – Michael Hampton Sep 16 '20 at 02:23

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The diameter measurement in an ETRTO specification is the rim bead set diameter in millimeters. You must use a tire with the same bead diameter as the rim of it will not fit. If you have a 622 rim you must use a 622 tire. A larger diameter tire will simply blow off the rim when you try to inflate the tube.

With regards to width, there is a maximum tire width depending on the width of the rims but the frame clearance is usually the limiting factor. See What is the maximum or minimum tire width I can fit on my bicycle.

Adam Rice
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Argenti Apparatus
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