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I just

  • had a puncture at the valve stem on my front wheel. 29 inch mountain bike
  • replaced the inner tube
  • had to leave the bicycle outside at the 90 degrees with direct sun for two hours
  • rode the bike for half an hour

and.. got another puncture at the valve stem . why?

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  • 1
    This looks to be a valve that is "secured" to the rim with a nut. It also looks as if the valve was pulled out of the rubber. Can you share your tube replacement procedure, especially wrt to when and how you position this nut? I suspect you may be tightening it too strongly, before even inflating the tube, but I might be mistaken. A circular tear like this in a tube could in my mind only be a result of user error or a bad/faulty product.
    – jayded-bee
    Aug 24, 2022 at 22:19
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    Do you have a Presta valve stem going through a Schrader-sized hole in the rim ?
    – Criggie
    Aug 24, 2022 at 23:40
  • @Criggie hmm, i didn't know that they have different hole sizes for presta and Schrader. do they? i think the original tubes were Schrader. its a 2022 trek marlin 4
    – yigal
    Aug 24, 2022 at 23:58
  • @jayded-bee . yes i did use the nut, i don't recall how strongly i tightened it
    – yigal
    Aug 25, 2022 at 0:00
  • Not duplicates, but relevant bicycles.stackexchange.com/questions/8157/… specifically Willeke's answer. And bicycles.stackexchange.com/questions/59/…
    – Criggie
    Aug 25, 2022 at 3:12

1 Answer 1

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I would suspect you've got a Presta valve stem passing through a Schrader-sized hole in the rim.

The Presta hole should be 6.5mm across, and the Schrader is 8.5mm That's not a lot of difference, but its enough for the air pressure in the tube to push the valve out the rim-hole a little, where it is cut or sheared off.

Measure the holes first to be sure, compare your front and rear wheels too.

You have three options:

  1. Buy a schrader-valve tube or two.

  2. Buy/make a spacer/bushing

  3. As a temporary hack, you can wind one of the retaining nuts onto the valve stem before installing into rim, and a second nut can go on afterward. Avoid overtightening either nut - fingertight is fine.

Then inflate tube like normal - probably 40-60 PSI for a MTB tyre on the road, and less for offroad usage.


Update - searching your bike brand returns

Rim - Bontrager Connection, double-wall, 32-hole, 20 mm width, Schrader valve

This reinforces the "wrong valve size" idea.

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    Thank you, I would never guess that you cant just put Presta valve in Schrader hole. I' just ordered a few Schrader tubes.
    – yigal
    Aug 25, 2022 at 8:35
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    @yigal coincidentally, today one of the four shared bikes at my workplace needs a new 26" tube, and all the spare tubes of this size are presta. I'm going to have to buy more or use some of the tricks above to get it usable.
    – Criggie
    Aug 25, 2022 at 9:51
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    I run presta valves in holes that are drilled for schrader, and I personally have never had an issue with the setup. Is this a common problem? I suppose checking the edge of the hole isn't sharp and buying new rim tape might be good work-around as well?
    – jayded-bee
    Aug 26, 2022 at 21:46
  • @jayded-bee I think its related to tyre pressure and the curve out the valve hole. If it was a road bike with 80-100 psi then it would cut easier than a MTB with 30-40 psi in the tube.
    – Criggie
    Aug 26, 2022 at 22:36

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