Will 225/45/17 on an 17x8'' rim fit fine on a mk4 astra 5 stud?
they will technically fit but youd be ill advised to fit them on a mk4
tyres are too wide and the profile will be too chunky
if your lowered the wide rim and bad tyre combination is gonna play havoc with the arches - especially if the rim has a low offset
YES they will fit though.
215.40.17 is the ideal tyre size - 8J x 17 is a little wide but if ur adamant then make sure the offset is 42-49mm if u plan on going low