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Must of had about 10 in the last few months, more in the front wheel than back.
It’s always the same split at the base of the valve and it’s happened to 3 different makes of tube.
I’ve got Halo freedom 29er rims and have checked the inside of the valve hole for burrs etc and both are okay, i’ve even tried putting a patch of old inner tube over the valve before I poke it through the rim to act as an extra layer but these never show any signs of rubbing as the splits always seem to start inside to tube.
Am I running my tyres at too low pressure? (the gauge is broken on my track pump so I only run them at usual quite squidgy pressure) however I have tried higher pressure but the splits still appear.
Am I tightening the valve to the rim too much? or too little? so the base of the valve is too free to move around?
Sorry for all the questions but I’m running out of ideas.
Help please stw collective!
Cheers ta

Tyres loose on the rim? Tubes sticking to the tyre and Dragging the tube round under braking and tearing the valve? Try some talc.

go tubeless simples

tyre moving under braking +1

I had exactly the same problem with halo rims. I reckoned the hole was just big enough to allow the valve to sink a bit too far into it.

I fixed it by padding the hole out with inner tube strips.

Are you using presta valves on a rim that’s drilled for schraeders? Try threading the nut down to the base of the valve before inserting the inner tube – it’ll stop it pushing into the hole and pinching the rubber.

I had this problem a few years back, sometimes only got a mile down the road and it would happen, I think the comment above might be right, put a mark on the tyre and rim and see if the tyre is slipping on the rim.
I think I ended up getting a new set of tyres, sorry can’t be more helpful.

Tyre moving on the rim for sure. Used to get this loads with old skin wall tyres. The only fix that worked was a couple of drops of super glue on the bead. It didn’t need much and only on one side so you could still fix a normal puncture. Not had it for years, though.

Thanks for the help everyone, I’ll double check the valve hole size.
It’s a chunkymonkey on front and smorgasbord on rear btw.

I’ve seen this if you’re not running enough pressure. I known you say you’ve tried higher pressures but without a gauge it might not be as high as you think. This is made more likely if you’re carrying a few extra lbs – no offence you understand 😉

Are you using presta valves on a rim that’s drilled for schraeders? Try threading the nut down to the base of the valve before inserting the inner tube – it’ll stop it pushing into the hole and pinching the rubber.

Or you can get a proper adapter to fit in the hole. eg something like this: http://www.ukbikestore.co.uk/product/91/wm0173/wheels-manufacturing-schreader-presta-rim-hole-adapter.html

I wouldn’t recommend that particular adaptor unless you’re happy to replace it with it with each new tube you buy. I had a set and they’ve corroded onto the valves v. fast. if valve hole and valve are different, get new tubes. schwalbe, for one, cater for every combination.

I’d guess at tyre movment either more pressure or talc
Some tubes come with talc on them ( mostly light weight )

Over tightening the lockring. It’s only to help prevent valve dive when fitting the pump, so it doesn’t need to be tight.

I’ve had this at various times on different bikes. I’m sure it is caused by the tyre rotating on the rim. Tyres that go on and off easily without levers are worse than others. Higher pressures definitely help, and pumping newly changed tyres up to their maximum PSI for a day to firmly seat them also seems to help.
I’ve never got a pinch flat (no rocks around here), but am seriously considering tubeless for this reason. Having to throw away tubes without a single patch on them seems such a waste.

Had something similar years ago when using a crappy old-school pump that screwed onto the valve. There was something wrong with the pump and it would twist the valve/tube weakening that area which would result in a split there later on. Only figured this out many unrepairable tubes later!