As title, would et20's fit onto a Fabia?

Dont think so..

I have ET35 with 8mm spacers that will be ET27 and it´s very close..

18"x7,5" ET35 whit 215x35x18 i have on my car, lowerd 50/40mm

Close as in to the outside arch?

17x7 et 20 would fit.

Yes, outside arch, dident find the word

cant even get my finger between the weel and arch!

17x7 et 20 would fit.

But that wasn't the question

They will fit, et15 16x9 fit mine, so you wont have any bother

So they will be right tight up against the arch??

Not a bad thing as i need to go higher a bit, might get some stretchy tires on