Hello

I have a question on wheel size and offset.
I saw people using 8x18 et15 on their Escort Cosworth.
If I want to use 7.5x17, should I be using et13?
I am thinking about using 215 45 r17 tyres.

Although I hate the idea of downgrading to 7.5inches, but
225 45 16 is hard to get a hand on unless order ahead.
Also, the tyre is rubbing the inner fender liner.

So, if I want to get that flush look with 7,5 inches alloy, I need to use ET13?
Thats according to the math, Im unsure of myself.

Cheers