Exploding inner tubes

Here is a problem I've never came across before.. I've bought a pair of Challenge Paris-Robaix wich is a 27c open tubular tire, weirdly flat and incredibly hard to put on the rim. Using Panaracer butyl inner tube in the 25c-28c size at the pressure of 70psi the inner tube explode, wich I think is because of the tire getting out of the bead. Same thing happened for both front and rear, in different places of the rim (Mavic Aksium).
Help.

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The wheel with the deflated weird flat tire on

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It wouldn’t surprise me that as the tyres are so tricky to get on the rim that you’ve pinched a tiny bit of tube. When you inflate them they go with a very loud bang

It wouldn’t surprise me that as the tyres are so tricky to get on the rim that you’ve pinched a tiny bit of tube

Or disturbed the rim tape.

It would surprise me, I'm quite ham fisted and after inflating the tire just a little bit i wiggled the whole tire on the rim, two times..

I also checked the rim tape, it did not move, I know, the mistery thickens

Assuming there are no sharp protrusions on the rim, @furious_tiles has offered the only explanation. Sometimes people get caught out with punctures when the object that's caused the puncture is still stuck in the tyre, and repunctures a new tube, but with new tyres, that's clearly not the case.

Well, not really, the other possible explanation is that the tire wont stay on the rim bead and at 70 psi it pops out and as a consequence the inner tube explodes.. Wich is still weird as I did not even use a little bit of water and soap..

Open tubular tyres can be a bit fiddly to fit as they come out the box so flat. A bit of air in the tube whilst trying to fit them and keep their shape can help, as can folding them a bit along their length. Tyres rarely blow off a rim if the bead has been seated properly.

Conversely, they're really easy to take off when you get a puncture. I can take my Veloflex tyres off the rim without tyre levers

diff tube + same tyre = see what happens
diff tyre + same tube = see what happens
?

That’s quite dramatic.

Check the rim tape. Was the tube stored with the valve cap off? Could it have become abraded in storage?

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My money is still on pinched tube

I used these tubes for several years with several different tyres, front was new, rear used. I've used them also with Panaracer Evo D tires wich are very rigid for a foldable tyre and even harder to fit than the Challenge and believe it or not, I've never got a flat. I will try with different tubes, you never know they might just be incompatible

So a pinched tube stays inflated for five days at 50 psi and as you try to inflate it at 70 psi goes boom in such a fashion? Not in my experience

When you pinch or damage a tube you create a weak area. After damage ... it can go pop whenever it likes :)

Was it ridden or just inflated to approx 70% pressure and stood?

If the latter then yes it will more than likely still be a pinched tube

My experience of Challenge beads was that they are stupid, stupid tight and pinching tubes was an occupational hazard

I am not infallible, I cant rule out I pinched 3 inner tubes.. there is always a first time, or three :)
It hasn't been properly ridden, only a few meters. What I find strange is that it happens every time at 70 psi and that the tire pops out of the rim, although I never got a pinch flat I dont think it necessarily happens, am I wrong?
I will definitely try a different inner tube

Hutchinson inner tube 25c, at 80 psi I watched the tire slowly going over the rim bead and I fretfully deflated it

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I popped it back in, inflated at 60 psi and stored it away, so that if it goes off again on its own I will preserve my coronaries

£2 will get you ear protection and save your hearing.

I’d check the rim for any fabrication burrs, especially around the spoke holes. The burst like that looks like it came out underneath from the tyre then popped, which is odd given its so tight in the rim.

They are stupid and not only stupid tight but also stupid smooth and slippery, apparently the problem was that to avoid pinching I used talc on the tube, some of it went on the tire bead which slipped off the rim when inflating.

maybe roughen up the edges of the tyres, when they`re new and unused they can be very slippery bc the surface is not worn at all. a few strikes with sanding paper on the bead will roughen up the rubber enough for the tyre staying on the rim. it worked for me several times.

This sounds like a good idea, thank you