will 18's fit onto my fabia with a width of 8j???

simon:)

yes with et of 38-42 ish and 205 tyres

will 18's fit onto my fabia with a width of 8j???

simon:)

Yes, you will require 215/35/18 tyres though

it'll be a bit of a squeeze. i have 17s on mine with 35's and its just right.

if you have 18s and you dont have it lowered you may require a rope ladder to get in it

i have lowered my car 50/40mm and runs on 18x7,5" ET35 with 215x35x18 tires and have 8mm spacers on, works fine