Tyre and tube sizing mis match...

[David9694]

...will my world cave in?

I’ve just changed to some 700x32 “gravel” tyres. They fit very nicely on the rims, but due to an ordering cock up, I’ve installed them on Scwalbe SV15 tubes that are specced up to 700x28.

For once, bigger tyres seem to be ok with my SKS/Bluemels mudguards.

Is this rube set-up going to cause me any problems?

[mattsccm]

Nah. Tubes vary anyway and often are labelled to cover a range of sizes. Maybe there is a perfect size and 19mm tubes might be stretched a bit thin in 42mm tyres but if it goes in then it will do.

[andrew_s]

If you can fit a tube in the tyre without it being either pinched under the bead or folded back on itself inside the tyre, it will work OK.

If the tube is on the narrow side, because it's stretched more, any puncture you do get will let the air out faster, and you'll have to stop to put a new tube in there and then.

If the tube is on the larger side (like an SV17), you'll generally at least be able to make the next gateway, and at least some of your punctures will leak slowly enough that you can avoid fixing them until you get home (or possibly even longer - for example I had a thorn in my tyre before Xmas, and only needed to pump it up every couple of days, until I picked up a second thorn that didn't plug its hole). The downside is that the tubes are a bit heavier.

[Redvee]

Had 38c tyres and 15c tubes on my bike recently with no problems other than having to move one of the tyres round the rim to eliminate a high spot.

[Roadster]

The question is begged, "If it doesn't matter, why do manufacturers bother to make tubes in different sizes?".
This is a rhetorical question, by the way, which means it isn't seeking answers.

[mattsccm]

Probably there there is an ideal or it may be the result of testing but its a very elastic ideal I reckon.

[Mike Sales]

The question is begged, "If it doesn't matter, why do manufacturers bother to make tubes in different sizes?".
This is a rhetorical question, by the way, which means it isn't seeking answers.

I hope you don't mind if I nevertheless answer.
If the tube is grossly too big it may be difficult to stuff it in. If too small it will be stretched and tenuously thin.
I have found a 26 x 1 3/8 tube in a 27 x 1 1/4 tyre. It was working fine.

[RickH]

A question that I don't know the answer to.

If you have a very undersized innertube compared to the tyre size, how much of your measured pressure is working to stretch the tube rather than support the tyre?

Is it likely to get significant, especially as bigger tyres are usually run at much lower pressures (I run 38mm Vittoria Voyager Hypers at 30F/35R)? I could envisage the possibility of a narrow tube not even filling the space of a large tyre but still registering the "right" pressure. I must dig out some skinny tubes that I have lurking somewhere & see (unless someone has already tried it).

[sjs]

Had 38c tyres and 15c tubes on my bike recently with no problems other than having to move one of the tyres round the rim to eliminate a high spot.

OTOH I had a Conti "race 28" tube in a 40mm tyre (as an emergency measure) which burst after a few hundred yards.

[Roadster]

Why risk wasting £3 on a tube of the appropriate size when you can just use any old thing you happen to have lying around? Far too much importance is attached to tyres, when it's obvious that only a small part of their circumference is ever in contact with the road at any one time.

[alexnharvey]

Why risk wasting £3 on a tube of the appropriate size when you can just use any old thing you happen to have lying around? Far too much importance is attached to tyres, when it's obvious that only a small part of their circumference is ever in contact with the road at any one time.

That tiny patch of rubber is all that separates us from disaster or a long walk home, and helped make cycling comfortable.

[9494arnold]

Few years Ago , on a group ride, one of the group punctured. On taking Tube out , (700c tyre, 23 mm)
I noticed it had 17 patches !!. I managed to convince the owner it had probably reached the end of it's useful life.
Having done that, as an expertise, I put another patch on then blew it up . I reckon it got about a 60 " diameter and was still going when I decided enough was enough. I realise it wasn't under the pressure of being enclosed in the tyre.

[Roadster]

Why risk wasting £3 on a tube of the appropriate size when you can just use any old thing you happen to have lying around? Far too much importance is attached to tyres, when it's obvious that only a small part of their circumference is ever in contact with the road at any one time.

That tiny patch of rubber is all that separates us from disaster or a long walk home, and helped make cycling comfortable.

Quite so, Alex, and if the irony was lost on you, that's exactly the point I was making. A clincher is useless without its inner tube so it's difficult to understand why anyone, in order to save such a small amount of money, would compromise on the one thing which allows the tyre to function.

[Mike Sales]

it's difficult to understand why anyone would compromise on the one thing which allows it to function correctly in order to save such a small amount of money.

Its possible to think of circumstances in which it would be useful to know how far you can push a mismatch.
Its also interesting.

[Roadster]

Sure, but finding out how far a mismatch can be pushed could easily get rather too... er, interesting.