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I just put an old set of tires and tubes back on the rims, and on one wheel, as I tightening down the Presta retaining nut (the nut that goes onto the valve after it's gone through the rim), I heard a loud hiss and the tire went flat.

I took the tire and tube back off the rim, and found the tube had separated from the valve right at the base:

enter image description here

It pulled away like that on both sides of the valve.

The tube was pretty old - I'd guess minimum 5 years of service.

The nut was tightened by hand only, specifically end of index finger and thumb. No tools, and no hand-tightening torque boosters like a cloth wrapped around it.

What I'm wondering is, does this indicate over-tightening of that Presta nut, or just an old tube that was ready to fail there?

To put it a different way, if I had a brand new tube with no manufacturer defects, would it still be possible to make it fail like this by tightening that nut just with my fingers? If so, how tight should that nut be to avoid such a failure?

Thanks.

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  • I personally never saw the need for these nuts, although I mostly ride "high pressure" tyres (upwards of 4bar), so the "inhibits valve movement" argument does not apply in my case.
    – arne
    May 2, 2023 at 16:13
  • The issue I find with not using them is it's hard to get the pump head onto the valve when the tire is flat because the valve wants to retreat into the rim when pushing the pump on. If you have a lot of valve sticking out of the rim, you can hold the valve to stop this. But in my particular case, my rims are medium depth but I've got very short Presta valves (purchased during pandemic supply difficulties). So there's barely enough valve sticking out to seat the pump head and definitely not enough to get my fingers onto the valve to hold it while seating the pump.
    – SSilk
    May 3, 2023 at 8:25

2 Answers 2

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Habitually tightening Presta nuts down hard seems to result in this. My speculation is that if it's really tight, the valve base area gets extra stress on it when the tire begins to lose pressure.

I don't think tightening by hand on a new tube would ever result in this.

I've had a handful of tubes fail this way eventually after being run in larger than intended tires.

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How big is your rim hole? I see this occasionally where a Presta tyre was used in a Schrader hole, and there's no support.

I've printed something like this to fill the space on the inside of the rim and it seems to be working.

enter image description here

https://www.tinkercad.com/things/2YfE8bW6fe1-schrader-to-presta-valve-stem-adapter

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    Good question. I'm not sure and I don't have any calipers to measure it precisely. Looking at it from the outside, it just fits the Presta valve. I don't think a Schrader valve would fit through. And there is very little play side to side. The wheels are Shimano WH-RS100 which are listed as being Presta compatible only.
    – SSilk
    May 2, 2023 at 7:45

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