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Using an undersized tube , what issues does this cause?

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Using an undersized tube , what issues does this cause?

Old 06-03-22, 11:44 AM
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jambon
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Using an undersized tube , what issues does this cause?

Hi there ,

Can I get away with a tube marked 35 c in a 44mm tire ?

What kind of issues if any would I have ?

Thanks
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Old 06-03-22, 11:49 AM
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ClydeClydeson
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It'll work because butyl tubes have the ability to stretch several times their unstretched size. However, the tube is stretched much thinner so flats will be more likely. If it's all you got, pop it in and ride to the bike shop or W*lmart to get a size closer to your tire, then keep the undersized one as a spare.
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Old 06-03-22, 12:13 PM
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The only time I couldn't get a glueless patch to work was in a similar situation. By the time I got the patched tube back in the tire and pumped it up to pressure, apparently the patch had almost set and then the tube stretched away from the patch as it was inflated.

Moral of the story? Always have a spare tube. And as Clyde said, get a tube that's closer to the correct size.
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Old 06-04-22, 07:34 AM
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Originally Posted by ClydeClydeson View Post
It'll work because butyl tubes have the ability to stretch several times their unstretched size. However, the tube is stretched much thinner so flats will be more likely. If it's all you got, pop it in and ride to the bike shop or W*lmart to get a size closer to your tire, then keep the undersized one as a spare.
Thinner tube is not much of an increase in flat likelihood. Thinner tube will mean slightly faster pressure loos.
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Old 06-04-22, 08:56 AM
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I agree with KerryIrons. If something gets through the tire, the minuscule difference in tube stretch probably isn't going to be the make or break factor in getting a flat. If I had to choose a tube a size larger or size smaller, I'd rather have the smaller for ease of mounting and being less likely to get pinched.
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Old 06-04-22, 10:47 AM
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OTOH rubber is a material that stretches most where weak or thin, so any areas of thinning or any
scratch on the rubber will disproportionately thin out more increasing the risk of puncture or leak.
Probability is you will be ok but depends on individual tube factors. (Once had a bent with 406
wheels with a 34mm tire and 25mm tube with microcuts all over it, tube flatted every ride
for 5 rides -slow learner- til I looked it over and noted the microcuts and tossed it).
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Old 06-04-22, 10:54 AM
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I've had good results using 18 to 28 mm tubes in 32 mm wide tyres.

Going for 37 mm was stretching it a bit and, depending on the pressure, tube getting stretched open can happen (tried it, with varying success, but wouldn't recommend it).

Yes, I'm aware that tubes do stretch quite much over their stated max tyre width, but it appears they don't really "like" being stretched too much.

Now, the question is: is the difference between 35 mm (if we assume that's what 35 c means) to 44 mm enough of a difference to make a difference.
I have no idea.
I'd feel comfortable using such a tube in a 37, or even a 40 mm wide tyre, but considering the cost of tubes, I might be tempted to give it a test with a 44 mm wide tyre only if I had no other use (wheel) for it. Just not on the front wheel.
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Old 06-04-22, 12:09 PM
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Some discussion of possible problems with thin tubes in wide tires in this thread: headscratcher flat
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Old 06-04-22, 11:39 PM
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Originally Posted by ClydeClydeson View Post
It'll work because butyl tubes have the ability to stretch several times their unstretched size. However, the tube is stretched much thinner so flats will be more likely. If it's all you got, pop it in and ride to the bike shop or W*lmart to get a size closer to your tire, then keep the undersized one as a spare.
I guess in theory, the smaller tube, stretched thinner might be weaker to punctures. In practice, I doubt it. Based on my experience anyway. I always use tubes at least one size smaller than the tire. Just making up numbers, but if it's a 25mm tire, I'll use a tube whose stated range is up to a max of 21 or 23mm. I've even used those size tubes in 35mm tires with no flats ever.

Anything that pierces the tire itself, will puncture a tube regardless of whether it's a tiny bit more stretched than a larger tube.

Also, getting a tube into a tire and that tire mounted is much easier with a smaller tube, much less to get pinched between the tire bead and the rim.
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