I have seen this photo already somewhere. Wasn't there a certain amount of debate about whether the rim and the tyre were actually meant to be tubeless in the first place???
well yes. At the time I think those tyres were (perhaps wrongly) being sold as tubeless compatible, and it seemingly wasn't understood that the hooked bead would do anything useful in the way of tyre retention; not consistently, anyway.
In fact I am still not sure that it
is widely understood; there are still folk suggesting that if you overpressure a tyre to test it, and it doesn't blow off the rim, that it is 'safe', and DT's recommendations (which I linked to upthread) appear to give tubeless tyres considerable benefit (in terms of pressure rating) when fitted to hook bead rims.
Now if the tyre always seals between the tyre lip and the rim well, maybe this is OK, and maybe this is what usually happens when you mount a new tyre on a new rim etc. But there is no evidence to suggest that this always happens in a real-world situation: All it needs is for the leak rate between the tyre lip and the rim well to be in excess of the leak rate between the rim lip and the tyre higher up, and the tyre bead isn't being pushed into the rim hook any more and the 'benefit' of a hook bead will be about zero.
This comparatively simple observation probably explains some of the 'mysterious' tubeless blowouts, even when the tyre initially 'passed' an overpressure test. In the meantime I take advice from all quarters (including from many manufacturers) concerning tubeless tyre pressures with a king-sized pinch of salt. If you default to the tyre pressures specified for hookless rims (whether your rims are hookless or not) and given a whole list of other 'ifs' concerning the quality of tyre/rim fit etc, then you may be reasonably safe. Otherwise... do you feel lucky...?
BTW to clear up a misunderstanding; when I helped my chum with a problematic tubeless fitment a while back, I only did so because I could see he was struggling and he was grateful for any help, even if it was just pumping the bottle up again (and again). I still don't know quite
how he found it within him to persist in trying to fit a tyre to a rim when the fit was clearly looser than it should have been (I'd probably have thrown the lot back in the face of the supplier, along with some terse angle-saxon phraseology), but I do know
why; he is a professional bike mechanic and he had a customer due in before too much longer. To my surprise he prevailed and the customer wasn't disappointed. He was (quite rightly) completely pissed off with the quality of the parts and lost money on that job; it should take a few minutes, not over an hour even two-handed. I don't know exactly how commonplace such occurrences are but there were dark mutterings of the kind that usually precede refusal to work on similar equipment subsequently (eg "if they are daft enough to want to use that crap then they can ****in' well do it themselves"). We shall see.
BTW this may fall into the 'very obvious' category but I didn't mention it previously: When you fit a tube into a failed tubeless tyre there is another significant difference from a tubed puncture. With a tubed puncture when you find something poking through the tyre you can be reasonably sure that you have just found the culprit. With a tubeless puncture this isn't the case: If the sealant has been working as promised, there may be numerous pointy things stuck through the tread, any one of which can instantly puncture the tube you just struggled to fit. So you must inspect the tyre very carefully if you don't want to have an immediate repeat performance (assuming that you even
have another tube, that is...). Obviously the inside of a tubeless tyre is covered in sticky crap and it is easy to miss something. In the workshop, if I want to be reasonably sure of a tyre, I need to clean all the sealant off the tyre, and then spend quite a long time inspecting it. [ I have known some of my MTBing chums throw tubed tyres away (eg having gone through a thorn bush) simply because they were not confident about finding every thorn (which can be entirely hidden within the tread thickness of course) no matter how long they spent.] Obviously any inspection carried out by the roadside is unlikely to be very good by comparison.