In the last two months I have experienced something new: three inner-tubes (700X25) have popped with holes immediately around the valve and on the same side of the tube as the valve. I suspect there is a deficit of support for the tube as the hole in the rim for the valve is slightly larger than necessary (1-2mm bigger in diameter that I would think best). Should I replace the rim-tape? How may the proper support be imparted to the inner-tube around the valve?
I had a bike shop for 10 years and have 35 years extensive riding and bike innovation experience. This problem had me dumbfounded: six tubes in rapid succession, blown inside the tire, within an hour or two of pumping up, with a dimple on one side of the the elliptical valve reinforcement, and a split on the other.
Cleaned up sharp edges on valve hole in rim, on spoke nipples, on rim strip--sure we'd got it that time, then "Bam!" After the fourth tube, I scoured the internet for the answer, saw dozens of accounts of this issue, dozens more theories, nothing definitive. Double rim strip, super clean...pumped it up..5th tube I was watching the valve core as it blew and the air leaked out...and the valve stem moved up and down in it's hole of it's own accord.
This sparked memory of "Useles's" herniated tube theory. 6th tube I followed the usual procedure, and tried to pull the valve down with the tire partially inflated. It pulled back-the start of the hernia was pushing it back up!
I deflated the tire further, pushed the valve up (to get the tube from under the bead), then pulled it down and it settled easily way further out than it had been. Pumped it up,no space for a hernia, no hernia, no blow out.
I had a spate of these; all the tubes had an elliptical, smooth rubber section immediately around the valve, and then a weld joining this to the body of the tube. The failure was always at this weld, and it looked as if the tube had herniated (bulged out in a single spot before bursting there).
After ruling out tape problems, burrs, sharps, valve hole diameter etc. - I finally figured out the problem.
The elliptical section is less flexible than the main body of the tube, so after pushing it above the bead as Zippy suggests, it wasn't fully descending to sit flush against the rim. This left a void between the rim and the less-flexible part of the tube around the valve; the more flexible section of the rim then tried to expand around the weld to fill this gap, and that's where it burst.
The solution is (touch wood) to pull the valve back down after the tyre is seated and the tube partially inflated, and tighten the nut more than usual (and then slacken off). When the tyre is fully inflated, double-check that there is no bump near the valve, that the bead is seated properly there, and that the valve doesn't move if you tug it towards the hub (not too hard!).
There are 3 things to try, in this order:
- Check the valve hole in the rim for burrs or sharps. It's possible that something left from the machining of the rim is cutting the tube.
- Make sure you are using the correct tube and valve style. There is not normally any significant space around the valve. If there is in your case, you may need to use a schrader valve in place of the presta valve it appears you are using. Check the diameter of the hole. 5mm = presta. 8mm = schrader valve.
- Make sure you aren't damaging the tube with excessive movement when inflating it. Use a floor pump, and make sure there is no excessive force on the valve.
It can also be the result of riding the tire while the pressure is too low. When you do that the tube tends to move in the tire and can get cut against the edge of the rim.
I hope that helps.
A picture would probably be very helpful. In particular, a close-up picture of the rim around the valve hole, with the tire installed and at least partially inflated.
I agree with the diagnosis of a Presta valve being used without a grommet in a rim drilled for a Schrader valve.
But it may be possible that more than one thing is causing your flats. When you install a new tube in a tire, the rubber holding the valve to the tube can get caught under the bead, and this can cause a flat. The remedy is to push the valve into the tire when you install it. What I mean is, push on the valve stem, like you see in the first 15-20 seconds of this video.
Too, sometimes the adhesive on rim tape is not good, due to age, oxidation, or the rim tape itself is poor quality (like the tape sold by a large national chain of bicycle stores). The tape can move around during the installation of a new tube, exposing spoke holes and/or valve holes. This can cause a flat. The best solution is to either use good rim tape, of the proper width for your rim, or, even better, to use a rim strip.
I had constantly the same problem with my Presta valve stems. Finally I widened the hole in the rim, inserted a rubber grommet and used a few turns of double sided hockey tape on the rim. Two years later and I never had this problem again.
I placed a large tube patch (centered over the valve) along the area where the tube quickly wears.
YES, NEVER install the nut when inflating a presta tube...you want the valve to stay far from the tire bead when inflating. If valve nut is installed before inflating the tube, the tube will blow at the valve area.