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I recently replaced my front tire. About 3 days post replacement I noticed that the pressure in that tire was at about 50psi (Its a road bike - I keep it around 120). I pumped it up and hoped for the best for my ride home.

I didn't have time to check for the leak that day so I left until the next day. Next day the pressure was fine.

about 5 days later it again dropped down to around 50 and I pumped it up.

Now its been about 2 weeks and the pressure is holding as well as it usually does.

Whats going on here?

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    I would guess that the valve was leaking. Generally a "slow leak" won't come and go like that. – Daniel R Hicks Aug 28 '14 at 18:02
  • I once had a sudden loss of air when I rode over a pothole, whick proved not to be a puncture. I'm convinced the force made the valve fail for a very short amount of time. Any chance that could have happened? (twice?) – PeteH Aug 28 '14 at 18:34
  • Similar question. bicycles.stackexchange.com/questions/23647/… do not agree with the conclusion of the question poster. – paparazzo Aug 28 '14 at 18:54
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Luck, most likely.

You probably have a slow leak, which you could treat by replacing the tube or just keep pumping air in as necessary. Less plausibly, theres something up with your valve. You could try taking the tube out of the tire and pumping it up with a bit of air and putting it in your bath tub to see if you can find some bubbles.

[In the comments, DRH has the reverse ordering on plausibilities]

  • Can't a slow leak be caused by muck in the valve on a presta? Pumping up would then have a chance of dislodging the muck. – Chris H Aug 28 '14 at 14:41
  • I think you're thinking of a schrader valve, @ChrisH. – JohnP Aug 28 '14 at 14:52
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    Or just take it out and pump it to 2x it's normal size. At that inflation even minute holes can be seen/heard. – Vorac Aug 28 '14 at 16:11
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    Could it be possible that the lock-nut wasn't fully secured the first two times, and the cap (if used) was slightly depressing the valve stem due to slight over-tightening? – digijim Aug 28 '14 at 16:15
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    The valve in that tube could have a bad seat. Every time you pump it up you move the valve stem in relation to the seat. Sometimes its seats correctly, other times it leaks a bit. It may work itself out over time. If it gets worse replace the tube. – Gary E Aug 28 '14 at 17:57

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