narrow rim = punctures ?

souter

Replaced the rear wheel on my commuter a few months ago and it's fine except when I come to change a tube it is divill to get the tyre beads seated around the valve.
Became accustomed to a perceptible bump which I can see and feel. Then yesterday the tube exploded around the valve stem.
I fixed it then lo and lo and behold the same thing happened today.
Not happy.
To my mind there is a connection between the valve stem not fully mating to the rim but I'm stumped as to how to remedy it.

I could try reaming out valve hole on the rim but my suspicision is with the valve/tube interface rather than the value/rim.

Anyway, any suggestions are welcome - I'm running a 25mm tyre on a fixie rear wheel, will post the specifics shortly.

doozerie

A perceptible bump is bad news, a pinch flat is almost inevitable in that situation and blowing the tube apart is very likely.

There is a knack to getting the tube seated properly within the tyre. It's not particularly difficult but any knack takes a bit of practice to get right. This is the way I do it, but there are many variations:
* Sit one side of tyre on rim.
* Partially inflate tube, just enough so that it doesn't flatten easily, and feed it in starting with the valve.
* Start fitting the other side of the tyre from the side opposite the valve. As you fit that second bead, make sure it's no sitting on the tube as you go around the rim.
* Fit the bead at the valve last and push the valve into the tyre as you do so, to ensure the bead doesn't rest on the tube there. If necessary let some air out of the tube for this bit. Ensuring the first bead is sitting in the channel in the centre of the rim can help here too.
* Go back around the entire rim, pushing the sidewall of the tyre to check whether either bead is resting on the tube.
* When satisfied, inflate the tube and go back around again to see if the tyre sidewall is lifting anywhere due to resting on the tube. If it is, use your thumbs to try to re-seat it, and resort to bouncing that part of the tyre on the ground if necessary as that can help the tyre settle into the rim.

If the tyre still isn't seated properly by the end of that, let the air out of the tube, pop the problem side of the tyre off, and try again. That's almost never needed though, in my experience.

souter

Pushing the valve in was the trick - I normally screw that in tight as a very first step.
I still start with the valve, I find getting the last bit of tyre bead in such a faff I wouldnt have enough pairs of hands to push in the valve as well.

souter

Just went outside to put the bike in the shed, admiring the new wheel, not even touching it, then psssshhhhhh - flat as a pancake!

souter

..turned out to probably be nick due to me doing a naughty and levering the tyre on.
Ditched the tyre in favour of looser one I can actually fit using my thumbs. At least if I puncture again it'll be easier to repair.