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?