9

I get many punctures at the valve stem in my 29 inch mountain bicycle. any tips to avoid them?

The hole with leaking air is marked with green circle (click for larger):

deflated tube held so the stem is bent to one side, revealing a hole in the reinforced part at the shoulder, which is circled in green

The rim with rim tape next to the deflated inner tube. The inner tube has indentation which does not leak air.

The tube stem alongside the rim looking down through the valve hole. The stem appears to be scored horizontally about 5mm above the base.

Non-perpendicular valve at the other wheel.

non-perpendicular valve at the other wheel

enter image description here

The back wheel after deflating, adjusting, inflating to 45 psi and short ride

4
  • 1
    Was the valve perpendicular to the rim? f not then that can cause this sort of thing.
    – Paul Lydon
    Commented Nov 4, 2023 at 18:53
  • The last photo is really disturbing. Not only is the valve at a very wrong angle ,but it also seems that the tyre does not really sit properly in the rim. Always check that the tyre bead sits well in the rim and that the tyre is pumped to the recommended pressure. Commented Nov 6, 2023 at 21:51
  • obsoletely is is disturbing, i have reseating the inner tube and increased the pressure to 45 and now it is stays perpendicular after riding
    – yigal
    Commented Nov 6, 2023 at 22:05
  • It might not matter at all, and isn't that hole caused by a tear or rupture, not really by a puncture? The difference being that looking for the cause of a puncture will presumably lead the mind to look at external causes such as nails or stones, but the pictures here seem to show a hole caused by internal weakness, whether they lie in the structure or, as others have suggested, in the positioning… Commented Nov 6, 2023 at 22:49

4 Answers 4

8

It seems the tube has tried to move (probably dragged by tire while braking), and the valve was trying to prevent it from doing that. The result of that is shear stress not only on the part of the valve going through the rim, but also (since valve is unable to change its position significantly) a force that tries to stretch / tear off tube from the valve.

One of the reasons might be incorrect pressure of the tubes. At what pressures are you inflating them, and what are pressure ranges specified on the tires? Do you check the pressure before each ride?

3
  • 2
    yes, that looks like that the problem, my psi was just 20 which caused the valve to become non-perpendicular after short ride. i have increased the pressure to 45 psi which solved the problem(for now)
    – yigal
    Commented Nov 6, 2023 at 22:02
  • 1
    @yigal some brands of Schrader-valve tube have locking rings like Presta valves. That may help hold the valve still.
    – Criggie
    Commented Nov 7, 2023 at 0:17
  • 1
    After about 10 km of riding in various terrains,including downhill with constant breaking. The valve is still perpendicular and without punctures. Lesson learned: always maintain high enough pressure to make the valve perpendicular. in my case 45 psi
    – yigal
    Commented Nov 10, 2023 at 23:35
12

The rim hole in the second photo has a clear curve of silver metal. That looks like a sharp burr left over from the drilling process, and it will slowly erode its way into your tube.

The solutions are any or all of:

  • Use a needle-file or a deburring tool to smooth that off (marrked here in Magenta)
  • Add a thin grommit that covers the sharp part
  • Fit new rim tape that covers the edge of the hole, or adjust the existing tape around the rim a few millimetres.

enter image description here

Also, notice the second gouge in your valve stem, marked in yellow. This comes from the other side of the dual-wall rim also eroding its way into your rubber.

It may be worth smoothing both holes as much as you can.

Also, I believe Schwalbe brand tubes have metal valve stems all the way up, which could help your rim.

2
  • 2
    Fit new rim tape that covers the edge of the hole, or adjust the existing tape around the rim a few millimetres. I'd personally shy away from that. I'd be too worried the rim tape might move a bit, or that it wouldn't be enough to keep the stem from rubbing against the sharp edge. Commented Nov 6, 2023 at 23:46
  • 1
    I should definely do that, but in low priority since the problem was solved by just incresing the preasure to maintain perpendicular valve.
    – yigal
    Commented Nov 10, 2023 at 23:37
7

I've had rim that caused punctures like that quite regularly. Covering the sharp edges of the valve hole with tape helped to some degree. Making them less sharp with a file or sandpaper might help as well.

As mentioned in the comment section, always keep your valve perpendicular to the rim, not pressing on the hole edge. However, for some rims you will get these kinds of punctures even if you try pretty hard to avoid them.

6

As others have pointed out, make sure to have the valve perpendicular to the rim at all times.

Secondly you could try make some improvised padding around the rim hole, especially if the edge in any way feels unusually sharp to the touch (rough rim opening AND/OR rim-tape?). Use your fingers. Consider buying some new rim-tape/band. you could also consider to gently sand the edge of the rim-hole by hand. This would be at your own risk, but doesn't sound too risky with some sand paper IMO.

Thirdly, could you use a shorter valve? The indentation on the rubber on the valve (best seen in the 2. pic) suggest that the valve has not been at 90 degrees all the time (unless this is some manufacturing artifact). If you inflate with a hand held pump, a long valve will give you high leverage at the valve/tube insert point. Making it easier to create tears it if you pump with a hand held pump without steadying the valve properly. Preferably use a floor pump or use a car tire pump at a gas station.

Finally, consider trying a different brand of tube that might have a stronger design in the problematic area, and be gentle when installing/inflating the tube.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.