Not wishing to scare anyone, but thought it best to post what has happened to me, could be just a one-off (or rather a four-off, in my case).
I have 235/35 ZR19 91Y XL's & 265/30 ZR19 93Y XL's, fitted to 8.5J & 9.5J wheels, they have done 7600 miles, have been run @ 39-41psi, and checked regularly, (I even check tyre temp before checking pressures FFS !).
I have discovered that all four tyres have splits/cracks, in the bottom of all the three wide grooves in each of my tyres, they are 3-4mm deep and go all the way round, and down to the cords
The splits are perfectly straight and it is as if they have been put in a Lathe and had a knife held against them.
Reported this to Continental, and they are being removed and returned to them for inspection, I will obviously report back, when they send me the report.
So please get a torch, and have a careful look in the grooves, to make sure you do not have the same problem, luckily for me, have only been doing town work lately, and not using it to it's "full potential", I could easily be a different story ! I am sure you have all seen footage of what happens when a tyre de-laminates at speed !
Meanwhile back to the 18" and Run-Flats, forgotten how bad they were, anyone dithering about the decision whether to change or not, just do it.
To end on a positive note, the rears have equal wear across the tyre (no inner edge where here), with standard M-Sport suspension & geometry, Quaife, and Hartge roll bars.
Get out there and check them PLEASE.