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I recently got two punctures in two weeks on my rear wheel. I use the carrera tdf with the kenda tyres supplied. The inner tubes I used were both quite short at the valve to the point that I could only just pump it up with my hand pump.

I would tighten the lock nut so that the valve was secure but I noticed before doing this that as pressure was released from the tube the valve would sink deeper into the rims. I was worried that this sinking effect due to decreased pressure would cause the inner tube to rip next to the valve if secured with the lock nut.

Can anyone offer an answer?

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    Did you inspect the tube to find exact place where it ruptured?
    – Klaster_1
    Apr 8 '15 at 10:42
  • If the pressure is too low in the tire you can get what's known as "snakebite" punctures from hitting curbs and the like. Apr 8 '15 at 11:54
  • You say "lock nut", which implies that you have Presta valves. The nut should be screwed on snugly, but not super-tight. One purpose of the nut is to hold the valve in place while you pump. Apr 8 '15 at 11:55
  • Do realize that Presta valves come in multiple lengths. If the valves seem too short you should replace the tubes with ones that have longer valves. Apr 8 '15 at 11:56
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Short answer: Probably not.

Long answer: While it is technically possible to construct, a scenario, where a tube with a presta valve would get damaged,because the valve is too short/the rim is too deep, in my opinion it is highly unlikely that this is what's causing the problem. The lock nut is great to facilitate pumping your tires, but not needed once the tube is inflated. Like many other road cyclist I know, I don't even install it. I and I have never had an issue because of this.

Generally you should look for tubes with a longer valve if you feel like the one you had was too short. AFAIK know they are available in three lengths. If you are experiencing recurring flats, you should investigate whether it always occurs in the same place and carefully examinate rim(and rim-tape coverage), and the tire.

It's not unusual for the source of the issue(for instance a shard of glass) to be inconspicuously stuck in the tire.

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Tubes are re-enforced with thicker rubber around the valve, so tightening the nut will not damage the tube. That part of the tube is pressed against the rim hole quite hard when the tube is inflated anyway.

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