I just noticed this distortion on my rear left tyre that must have been caused by hitting a pothole or something - there's an even smaller distortion on the front left tyre. It's barely perceptible and I think I only spotted it because of my engineer's eye trained from hours of filing metal flat as an apprentice years ago.
I don't, however, know much about what's safe and what isn't with car tyres and this is bothering me. On the one hand, most other people wouldn't notice this and would carry on driving in blissful ignorance and I've already driven hundreds (maybe more) km at high speed on the motorway and on fairly windy roads. And these R18 255/45 tyres are very expensive at ~£200 a piece. On the other hand a tyre blowout, even with runflats, is something I'd rather avoid.
If you look at the inner line next to the alloy and the outer line just in from where the tread starts you can see the distortion. The surface of the tyre wall is also visibly uneven, if not quite bulging.