19/11/2025
Today, a shorter piece (who said "Thank God"?) to try and cut through the confusion of tyre sizes.
We are so used to them in the trade that we forget how obscure the subject is but then I see the blank look when someone asks for a tube for their 700x45 hybrid tyre and I blithely say "700x45? - I'll give you a slim 29er then as the hybrid tubes will be a little narrow. Is it Presta or Schrader ....?"
Firstly, be aware that 700c (and we can drop the "c" bit now as everything 700 is 700c - and no I won't explain the "c" bit as I really am trying to keep this brief) is the same as 29" MTB. You see, mountain bikes have American heritage and they won't deal in mm. The important bit is not the 700mm or 29" but the 622 number that is usually embossed on your tyre in numerals so small you can only read them with the aid of a torch and magnifying glass.
622 is the tyre bead diameter - where it seats onto the rim - in mm and the number after it is the width of the tyre, so, a common road bike size might be 622-25. This is the ETRTO number - a numbering standard that cuts through tyre size chaos. So why is it so much smaller than 700 which is also written on the tyre? Well, 700mm includes the whole tyre. But clearly, for those at the back not already asleep, a bigger tyre - fat hybrid or mountain bike - will give a much greater overall wheel diameter than a slim road tyre so the 700 is just very approximate - which is where the "c" bit comes in but, no, no, I'm not going there, I did promise.
Nowadays - in adult bikes - we have old 26" (MTB that is - there was an older English 26 which was quite bigger) which is 559mm, 27.5, mainly used for MTBs, at 584, and 622 which is road bike, hybrid and 29er MTB.
To really confuse things, many German brands insist on believing that in the UK we call 700 28". We don't and never have. We did used to have 27" (nothing to do with 27.5 MTB) which is 8mm greater diameter than the 622 of 700; so on their reckoning we would be calling a tyre 28" that was smaller than our old 27". Hmm. I've had customers reading this on the inner tube box and returning it as "This is a 28 and I wanted a 700."
You're getting it now I can tell: 622 is 700 is 29er, 27.5" is smaller than old 27", 26" is old MTB and smaller than all of these including old English 26 and 28 does not exist at all other than as a very old English butcher's bike size and in the minds of some European suppliers. So, all as clear as the mud obscuring the tiny figures trying to tell you the actual size on your tyre.
Thus, when wanting to buy a tube or a replacement tyre, forget 700, 29er, etc and always quote the ETRTO number - it's much more accurate - and use the number on the tyre, NOT the tube, as that is a much better guide as to what you need than the tube size as that just tells you what someone stuffed in there sometime ago because it was all they had to hand.
Glad we got that cleared up then!
