erm, as topic heading really please my fellow Ford fanatics!

(please bear with me cos i been out with Mr.Jack daniels for most of the night )

a mate of mine is after 17inch OZ super tourismo rims for his S1 RST but they are only available new in a focus ET48 offset.
im sure they is no good due to arch clearance but im lost by offsets,
im sure the more offset means they stick out the arches more.........

anyone shead any light on this as offsets really puzzle me, they shouldnt do because of my line of work, but we wont go there PMSL

thanks in advance,

Sean.