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Related: Patch or replace tube?

This video asserts that:

  • A properly patched area of a tube is stronger than intact tube area
  • Never patch a tube more than 3 times

Those are seemingly contradictory.

The video is just and example and motivation for this question. I have often seem people discard tubes with several patches, after they are punctured again.

Is it true that after some number of patches to a tube, it is better to dump the thing? How many?

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My rule of thumb is the following:

  • Never patch a patch: when a puncture is too close to another patch so that the patches would overlap or almost, then I toss the tube
  • Never patch too close to the valve: the valve makes is a structural anomaly in the butyl that makes the tube, so is a more sensitive area, not to mention all the air input comes from there so it is a less stable area.
  • Toss a tube that has more than 8 patches... it is an arbitrary number but it is the one I set. Most of the times, when you reach that many patches, you will bump into one of the first two points,...

Of course, when in trouble, when you have no spare tube, and you have a flat, patch it no matter what. That is a no-brainer.

A properly patched area might be stronger than the intact area since it fixes the hole, but apart from the hole, it adds some thickness to the tube so puncture resistance.

You will (almost) never puncture a patched area: the patch might fail, but you will not puncture the patch.

That downside of the patch is that it does not expand (or just very little) compared to the intact tube (try to inflate a patched tube outside of the tire, you will see the diameter is smaller in patched areas). So an overly patched tube will be less expandable in the tire than an intact one.

This causes the whole physics of the tube inside a tire to be less perfect than it is conceived for; which is why you must not over-patch a tube (and solves the apparent contradiction).

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  • I like 8. Although I've patched 10 times once.
    – cherouvim
    Aug 28, 2013 at 9:34
  • Remember if you're getting multiple punctures in the same place repeatedly, the cause is probably stuck in the tyre. This is handy if you choose to line up the tyre's logo with the valve, because it gives you about 50mm of tyre to flex and search for the cause, be it wire or glass. Punctures should be randomly distributed.
    – Criggie ♦
    Feb 4 at 11:54
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Yeah, I'd essentially agree with Tisek. If the patches were very evenly distributed I could see going to 15 or even 20 patches, but they never are, and the uneven expansion that results puts additional stress on the tube and may also cause the wheel to be lumpy.

However, with belted tires I get punctures so rarely that I figure a tube is getting too old after 3-4 patches. (Especially since I always carry 2 spare tubes, one in my tool bag and one in my pannier, and rotate them.)

I would add that I'd never (except in an emergency) attempt to patch anything resembling a blowout (even a small one). (Though I have been known to put a patch on the inside of a tire to "boot" a small puncture hole.)

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