Cannot understand why you have paid £120 each for such an unknown tyre? There has been various posts of late about tyres and if you had done your research you would be sat on Goodyear F1 asymmetric 5's. I paid £125 for 18" 255/35 and just £90 for 18" 225/40.
It was also a good time to ditch the awful runflats.
Regarding your issue, I have experienced this before. The sidewalls could be very flexible and as soon as you put some steering input the sidewalls flex tricking the stability sensor into thinking you are sliding. I have had this with Dunlop's on an rx8, I couldn't apply hardly any power in a bend without the stability control kicking in, changed to vredestein within weeks and issue solved.
On the zed it could well be your alignment is out. When I had new Goodyear's fitted just on the rear the handling was as you have described. The zed has a lot of rear camber dialled in by BMW to make it safer by understeering. Your old tyres will have worn at an angle due to excessive rear camber, by fitting new tyres I believe the tyre footprint is reduced until worn and this affects the stability.
I would have your alignment checked and set to csl, this has completely cured my zed and totally transformed it.
It was also a good time to ditch the awful runflats.
Regarding your issue, I have experienced this before. The sidewalls could be very flexible and as soon as you put some steering input the sidewalls flex tricking the stability sensor into thinking you are sliding. I have had this with Dunlop's on an rx8, I couldn't apply hardly any power in a bend without the stability control kicking in, changed to vredestein within weeks and issue solved.
On the zed it could well be your alignment is out. When I had new Goodyear's fitted just on the rear the handling was as you have described. The zed has a lot of rear camber dialled in by BMW to make it safer by understeering. Your old tyres will have worn at an angle due to excessive rear camber, by fitting new tyres I believe the tyre footprint is reduced until worn and this affects the stability.
I would have your alignment checked and set to csl, this has completely cured my zed and totally transformed it.