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I got a 700x18-23 inner tube that just got punctured. The small round patch on my patch kit is a bit wider than the inner tube itself. Is it ok to cut around the patch so it fits?

An added question: when buying an inner tube, should i buy the smaller 700 x 18-25c, or the 700 x 25-32c for my 25c tires?

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  • Your second question is already answered elsewhere on the site. Short answer is "either's fine" – Criggie Apr 2 '19 at 19:29
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Don't cut it. The patch is thinner at the edges and cutting leaves a thick sharp edge where it can tear. Roll the tube sideways and you can glue first one and then other edge. There are smaller patches that are made for narrow road tubes.

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    My advice for a long time has been to just buy a 100-count box of Rema F0s if you're someone that patches, regardless of tire size... – Nathan Knutson Mar 31 '19 at 22:37
  • Thanks. I haven’t found any Rema available so far here, but if i do, i’ll purchase some. – Lefty Apr 1 '19 at 18:33
  • Finally found me some 15mm patches from zefal. – Lefty Apr 3 '19 at 18:03
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My experience has been the same as zeus; I've been cutting those bigger patches in half for decades.

However, I have had a couple of these peel up on the thick cut edge, long ago. That led me to taking more time with such patches: making sure that the tube is well abraded and partly inflated, that the glue runs right to the edge, that the edges are firmly pressed into the underlying rubber. With these precautions, I never lose air on a cut patch.

However, if I was stuck doing a roadside repair, I would always choose a whole patch.

(As an aside, why do they include those monster size patches in a bicycle tube repair kit anyway? If a hole was big enough to need a patch that big, you'd never be patching it.)

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  • I've used the monster patches a couple times, for Really Big cuts and once for a weird 10 holes in the same area. That one looked like it had been stabbed repeatedly with a compass by a vandal. – Criggie Apr 2 '19 at 19:28
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You don't need to cut it just because the patch is slightly wider: you can wrap it around the tube. Just before I put the patch on (that is, when the applied glue dried somewhat), I pump up the tube a bit so that it expands roughly to the size it would be inside the tyre. This allows to apply the patch easier, esp. if it's oversized, and also presumably avoids unnecessary stress (or rather, stretch) on the patch at full pressure.

That said, I frequently cut patches. The typical kit contains several long patches which never get used in full: if you have a cut that big, it's better to replace the tube. So I cut them in 3-4 smaller pieces. I never had a problem with the sharp cut-off edge, whether I put it along or across the tube, even on the 700x23 high-pressure road tyres. And I have decent statistics: I estimate roughly 10000 km with at least one patch cut like that.

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  • 10000 km, wow. It’s effective then. I’ll experiment on an old mtb inner tube with a cut patch. As for the rb tube, i’m gonna use it as a spare only, and just roll it up. – Lefty Apr 1 '19 at 18:39
  • MTB (and any such) tubes can be patched with almost anything: off-cuts from an old tube, self-adhesive patches, etc. If done properly, they'll be fine. Road tubes are more demanding: you need self-vulcanising patches. My tactics is typical: get a puncture, put the spare tube which I always have, fix the other one at home and make it the spare. I replace them after perhaps 4 patches. Thus I end up riding with patched tubes most of the time, and most or at least half of the patches happen to be cut manually. – Zeus Apr 1 '19 at 23:23
  • Finally found 15mm patches from zefal. I’d still experiment on my old inner tubes with cut patches, see how it goes. Thanks guys. – Lefty Apr 3 '19 at 18:06

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