I've a NB MX5, currently have 15x8 ET10 wheels on a 195/50/15 tyre.. The hub/fender measurement is around 10". I've also rolled the arches out quite abit, at least 1cm wider.
Only problem I have is on some bumps I get scraping from the tyre in the arch, I assume it's coming from the bracket between the wing to the bumper.
I watched a video on Youtube of rolling the arches and he mentioned that he cut this bit off and cable tied the bumper on instead, another friend though has said I should adjust the caster to bring the wheel slightly further back in the arch away from the bit it's catching on.
Hopefully this makes sense! The bracket is where the red line is on this picture;
(I have searched, but couldn't really find any advise..)