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I bought a used bicycle; it is all fine but one problem that I am having is that its front tire always flattens in about 5 or 7 days after I put air in it. I don't know what's causing this. Is there a way to fix it or know the reason it's happening? Further there is not any hint of leakage also holds pressure for up to a week.

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    Inner tubes are not expensive. Repairs are fine, but on a used bike you're often better just picking up a new tube and then it's a known quality.
    – Richard
    Mar 29 at 16:32
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    A friend got through three new tubes in a couple of weeks -- the tyre pressure was fine until he rode it. Turned out there was a thorn broken off in the tyre. It only worked into the tube when the tyre flexed while being ridden. I only found it by marking the tyre relative to the valve position, finding the leak in the tube, and measuring where it was. Couldn't even see the thorn, found it by touch. Mar 29 at 16:59
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    @Richard that's a separate debate - I've had brand new tubes fail out of box, and conversely a tube with 15 patches still working fine.
    – Criggie
    Mar 30 at 20:47

5 Answers 5

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Not an uncommon kind of puncture. A very small hole in the tube can take weeks before the tire becomes flat. It can also be caused by a leaking valve.

Use soapy water to wet the valve and look for a bubble forming, if that does not suggest a valve leak, remove the tube, pump it up a bit (expand it to about twice the size) and place in water, looking for an air bubble forming. (lots of help on internet how to locate holes and patch tubes)

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It's either a slow leak or a loose valve core. Slow leaks are notoriously difficult to find.

Do note that high-pressure bike tires anyway need pumping up once every two weeks since the pressure drops by nearly 30% in two weeks. Moderate-pressure tires may need pumping up once every 3-4 weeks.

However, if the tire completely flattens within a week, it leaks faster than it should.

If you have removable valve cores such as with Presta or Dunlop, first check that the valve is tight, you tighten it either with your fingers (Dunlop) or a small adjustable wrench (Presta). Also in case of Dunlop valves, some cores may be very cheap and leaky.

If it's not a loose valve core but a slow leak, the easiest way is to simply buy a new tube. Slow leaks are notoriously difficult to find.

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    The time between needing to pump seem also to change with the tube tyre and tube size, the narrower the more often it needs a top up.
    – Willeke
    Mar 30 at 8:14
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    @Willeke yeah - the narrower the tyre, the higher the pressure, and this increases frequency of topups because 1) higher differential and 2) less air reservoir capacity overall.
    – Criggie
    Mar 30 at 20:46
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If it keeps happening after you've installed a known good inner tube, make sure that your installation procedure is correct (you're not damaging the inner tube when you're installing it), and the tire is free of anything that could damage the inner tube.

For example, I once had to enlarge the hole on the rim to fit a larger valve, and one metal shaving found its way to the bottom of the tire.

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You probably have a spoke jutting too far through the rim which is puncturing the tire.

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    this method of puncture would deflate a tire rather quickly. It would not take 5-7 days to go flat.
    – Ted Hohl
    Mar 31 at 0:08
  • Welcome to the site. Good idea - if this was the cause, the hole in the tube would be in the inside-face. @ognam have you found the hole ?
    – Criggie
    Mar 31 at 1:23
  • Also check the inside of the tyre or the rim for any small sharp object. Running your finger around the insides will normally find it
    – CSM
    Mar 31 at 16:34
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All the answers here are so predictable and sensible.

Here one that is possible: Have you annoyed anyone in your neighbourhood? They could be taking revenge by puncturing your tyre.

Or perhaps the tubes came from a bad batch - try another brand or shop.

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  • Welcome to the site - You raise an excellent point. I've tweaked the wording a little.
    – Criggie
    Apr 1 at 18:31

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