20-25 tubes in 28mm tires??

[ndwgolf]

Is it okay or just plain stupid to put 20-25mm tubes in 28mm tires??

Neil


I'm a trendy consumer. Just look at my wobbly bog brush using hovercraft full of eels

[sylvestermorgan]

This got mentioned on a GCN video I watched on Youtube recently. It's basically a no-no because as you pump up tyre the inner tube will stretch to fill the void of the wider tyre making it more likely to fail (or so the explanation went). I'm sure others on here can explain it much better than I!

[The utility cyclist]

So long as its a correct 28mm and not pretending to be 30/31mm on a wider rim then IMO you'll be fine. Have been using the bog standard 19/20-25mm tubes in a 28mm (that measures 28mm) for 9 years on my everyday bike and I also use one on the front of the audax/tourer for the same tyre that's done a fair few miles without issues and before that when I tried Conti 4 seasons in a 28mm (though they came up narrow) I was also using a 20-25mm tube.

if it really bothers you you can go for the next level up, Race Wide is what Continental call theirs, it's designated as a 25-32mm, that's what I use for my 32 and 33mm tyres, Bontrager and Mavic also do a mid size tube, I think Raleigh have some branded ones on ebay that are in that range, about £24 for a box of 10 IIRC.

[The utility cyclist]

This got mentioned on a GCN video I watched on Youtube recently. It's basically a no-no because as you pump up tyre the inner tube will stretch to fill the void of the wider tyre making it more likely to fail (or so the explanation went). I'm sure others on here can explain it much better than I!

That's the thing, in theory they might be right in terms of 'more likely', in practise it's not something that I've experienced and I bet the failure rate over and above that of other tubes is negligible if indeed noticeable at all.

The problem is now that we have a similar scenario but in reverse to BITD, tyre manufacturers are now stating their tyre is xxmm wide, yet on wider rims are coming up significantly wider. The width of the tyre laid flat (before they put the steel bead in) should be how we make direct comparisons to tyre widths.
For instance, I've fitted a pair of 28mm Panaracer Evo As to a pair of H+SON TB14 rims for my new build titanium, they are coming up at 31mm, so I've used a pair of Race wide (25-32mm). I suspect on my 14mm Mavic Open pros they'd be closer to 28mm which is what the 28mm Giant PSL2s come at at exactly. I didn't want a 31mm tyre, I wanted 28mm so it's somewhat annoying that despite it being a newer tyre that has in mind the wider rims that it is coming up far wider than expected. I realise for some this may be a bonus but it's very tight under the mudguards which means I've had to dip into the pocket and buy some TRP dual pivots as these gain a fraction in the arch over the Shimano Ultegra long drops.

[Brucey]

you can do it but the tube will be more stretched than normal. This will increase the chances of a puncture (including annoying and unfixable ones such as splits on the inside, valve failures etc) and when you do get one the air will come out faster (because even a pinprick in a stretched tube will open up ). You can partially mitigate some of the potential problems by being sure to use plenty of talc on the tube when fitting it.

Needless to say one of the failure modes that is made more likely is that the tube just splits and lets all the air out very quickly. Since this is both inconvenient and potentially dangerous (it could happen on a fast downhill stretch or in traffic) it is not a good idea to increase this risk.

In a nutshell it is OK to use the wrong size tube in an emergency (eg to get you home) but it is somewhere between 'bad practice' and 'very stupid indeed' otherwise. Any increase in failure rate is a pretty poor trade if the 'benefit' is saving the price of an inner tube.

cheers

[MikeF]

This got mentioned on a GCN video I watched on Youtube recently. It's basically a no-no because as you pump up tyre the inner tube will stretch to fill the void of the wider tyre making it more likely to fail (or so the explanation went). I'm sure others on here can explain it much better than I!

Do you mean this?
I've been running a Michelin A2 tube in a 700x35mm Hyper. It possibly loses air slightly faster.
I'm not sure puncture resistance is affected by the inner tube thickness, but editing this I see Brucey thinks it does.

[9494arnold]

I often mix and match wide and narrow tubes (and use 700c tubes in 27" tyres) and I haven't noted any significant puncture instance that can be attributed to this practice.

Few years ago (just before Kevlar Belting gained popularity) you used to be able to get "Puncture Resistant" Tubes (Specialized?) the rubber was significantly thicker on the outside diameter. So that would seem to be the theory, thicker rubber less problems.
Never punctured one but they pulled valves out eventually (probably my fault for not keeping pressure at recommended levels, I was young and feckless then) and they seemed to die a death when tyre technology improved.

[andrew_s]

An under-sized tube works OK, but is more vulnerable to damage such as chafing on the edge of the rim tape or an exposed spoke eyelet.

Also, if you do get a puncture, it will be faster and more definite - an unstretched tube may seal around a smooth thorn, or a small flint may initially give a slow puncture that allows you to get home, but a stretched tube will go flat more or less immediately.

[Marcus Aurelius]

The tube should stretch to fill a 28 mm tyre without too much fuss. But as has been said, make sure it’s a ‘true’ 28mm tyre.

[foxyrider]

The Wilko tubes are impressively thick and as they do 20/25 and then 32/45 if you have 28 it's Hobsons choice!
I wouldn't normally buy tubes there but I needed one urgently and it was the nearest option.

[The utility cyclist]

you can do it but the tube will be more stretched than normal. This will increase the chances of a puncture (including annoying and unfixable ones such as splits on the inside, valve failures etc) and when you do get one the air will come out faster (because even a pinprick in a stretched tube will open up ). You can partially mitigate some of the potential problems by being sure to use plenty of talc on the tube when fitting it.

Needless to say one of the failure modes that is made more likely is that the tube just splits and lets all the air out very quickly. Since this is both inconvenient and potentially dangerous (it could happen on a fast downhill stretch or in traffic) it is not a good idea to increase this risk.

In a nutshell it is OK to use the wrong size tube in an emergency (eg to get you home) but it is somewhere between 'bad practice' and 'very stupid indeed' otherwise. Any increase in failure rate is a pretty poor trade if the 'benefit' is saving the price of an inner tube.

cheers

By how much?

[Brucey]

you can do it but the tube will be more stretched than normal. This will increase the chances of a puncture (including annoying and unfixable ones such as splits on the inside, valve failures etc) and when you do get one the air will come out faster (because even a pinprick in a stretched tube will open up ).....

By how much?

Enough to make a difference.

If you want to try an experiment, try cutting rubber sheeting when it is stretched and not. It is far easier to cut when under tension. This approximates to (say) flints poking through a tyre into an inner tube, or something chafing inside the tyre.

cheers

[Ray]

You may well be OK using unpatched undersized tubes, which will stretch to fill the tyre, but once the tube has been patched it is much more likely to fail due to excessive stretching. This is based on experience, not theory.

Given that new tubes are pretty cheap, using undersized tubes seems false economy.

[CJ]

I'm not sure puncture resistance is affected by the inner tube thickness, but editing this I see Brucey thinks it does.

Me too, and neither of us (I think) are so concerned about thickness per se, as what you might call 'stretched-ness'. I don't even like to use a tube at the upper limit of its recommended range of stretch.

[simonhill]

If using large or even oversized tubes on wider tyres at lower pressures - are you more liable to get pinch flats?

My (probably wrong) logic has it that a smaller tube would be less liable.