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Smutmaster General
Possibly one for "know how", but I'm sure cafe cats can give me a quick answer:
Looked in my saddlebag today and the spare tubes I've been carrying for about 4 months, since last p*nct*re are 700x19-23. Tyres are 700x25.
How I got them, I don't know! :?: But will they do to get me home, should I need them?

Steve Austin

The Marmalade Kid
yes they will be fine, maybe not for the long term though


Well-Known Member
I take the approach of - if they are vaguely round they'll do. MTB tubes seem happy in my 700c tyres and 700c tubes work (with a bit of stuff over) in my 18inch tyres OK. As long as your not trying to get something with a stupidly small diameter into a large tyre then you should be fine.

Quite some time ago they had a compertition at my club to see how big they could blow up a 27inch inner tube. IIRC they managed to get 5 or 6 people stood comfortably in side the tube and it was still capable of taking more air.

Steve Austin

The Marmalade Kid
can have a quite a few issues if you put a 2.2 inner inside a 1.5 tyre. it will blow the tyre off the rim and it will make you jump.

it will explode and makes a right loud bang :?:


Über Member
steve, is an extra inch of rubber circumference really able to do what 6 atmospheres can't? :?:

i've never tried it, but find it very difficult to believe, unless of course the tyre bead wasn't hooked in correctly, but then the correct sized tube would have the same effect

Steve Austin

The Marmalade Kid
I'm still in shock thinking back to it. It was vredstein s-lick tyre on a mavic rim.
Didn't think to look at the inner tube, and happily started pumping it up. Got to about 80psi, undid the pump head, and then BANG :?:

The tyre had popped off the rim and the inner tube had a great big hole in it. It was seated on the rim properly as i always rock tyres on the rim after ten psi. Just too much pressure somewhere and it blew the tyre off. i won't be doing it again. It may have been more than 80 psi and may have been that i just went a bit silly on the pressure, but its not worth running wrong size inners for long periods of time ime

Cheddar George

oober member
Recently had a blow out on my road bike which could be heard over half of Warwickshire. Bought a couple of new tubes from my LBS when i got home and asked for 25x700 (being the size of my tyre). The guy was taking them off the shelf and asked me if it was a proper road bike and then promptly put them back and gave me 18-23x700. Mind you his name is P Biggs so i didn't like to argue..........


Legendary Member
If the tube is considerably bigger than the tyre, just rocking the tyre on the rim at 10psi may not allow any bits of pinched tube to drop back inside the tyre like it would if they were the right size.

If the tube is a smaller size than the tyre, the only disadvantage will be that it will puncture more easily. If it's too small a diameter as well, it's difficult to get it fitted in place - I once found that my Michelin A2 (700x28-35) box had a B1 (650x18-23 long valve) tube in it.
I repaired a flat earlier this week, used the bike for 15 miles the following morning, then found it had gone flat again just tonight.

Obviously a slow puncture, wasn't sure if it was my repair or perhaps there was a second hole I'd not fixed, so I pulled the tube out, pumped a bit of air into it and had it in the sink looking for bubbles.

BANG :?: Suddenly just split.

That woke me up.

It wasn't like I'd put a lot of air into it, just pumped it up to roughly the size it would be in the tyre casing.

Decathlon own-brand Blue Bargain tubes, dead cheap. Perhaps there's a reason.
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