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After I changed tires to conti 4 seasons in my road bike, the front wheel has been leaking air very slowly. I've changed tubes some 3 times already, and it keeps happening (after a couple of weeks). The tube will keep some pressure for about 3 to 4 hours before it's noticeable. Submerging the tubes in water doesn't help to find leaks, and the back tire is fine. I checked several times and found no sharp objects inside the tire.

The only thing I did find a bit weird was that the rim tape was not exactly on the center on one point, and would not stay in the center easily (it kept climbing the inner wheel).

  • Did you change tyre size? Are you using 18-23c tubes on 28c tyres now ? – Criggie Jul 15 '16 at 1:15
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    yes, I was on 25c and changed to 28c – Matías Guzmán Naranjo Jul 15 '16 at 5:28
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    When changing tyres it's a good idea to check and maybe to change the rim tape as well, especially if shows fitting problems. – Carel Jul 15 '16 at 6:46
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There are two ways for air to leave a tube - an actual slow leak in the rubber or a faulty valve.

Since you've checked the tube and changed it. this could be a technique thing where you're pinching the tube creating a small hole that is not big enough to show up in a water test.

Try inflating your naked tube to a pressure of about 10 PSI. It will double in diameter, and could burst if you go too high. Mix some dishwash liquid into your lukewarm water to help break surface tension. Put the tube into the water, starting at the valve, and work around the whole thing. Flex the tube back and forth and take time.

A slow leak is hard to find, but its probably there somewhere.

Last chance is your tubes are all super-light and the air can permeate the surface. If this is the case, buy heavier tubes.

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    Yes, there are fancy-dancy ultra-thin racing tubes which won't hold air for 24 hours. You'd have to go out of your way to buy those, though. – Daniel R Hicks Jul 15 '16 at 1:42
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    It turned out to be the valve. – Matías Guzmán Naranjo Jul 15 '16 at 21:43
  • @MatíasGuzmánNaranjo Nice work and good spotting. Some presta tubes have a valve core that is removable, you can identify them by flats on the smaller thread. If you have this, unscrew it and try lubing the seal with something for rubber, or swap out the valve core with a spare. I save old cores from unpatchable tubes. – Criggie Jul 15 '16 at 22:43
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I would check your tire for tiny tears along the sidewall. I had a problem with my tubes leaking as well until I figured out that the tube was expanding into the tear of the sidewall and getting pinch flatted. Although, a slow leak is a little strange. If you don't see any tears in your tube, try replacing your rim strip, since it does seem to be acting weird. If that doesn't work, double, triple check for sharp things in your tire and metals bits sticking up on the wheel. Good luck!

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Check inside of tire for a prick with finger. Do the same for rim liner and rim. It could be a metal shaving or glass.

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