2009 A3 wheel change (offsets)

Hi, I have an A3 sportback 5 door 2009, the wheels are getting properly scrappy now and need a refurb. I'm thinking of buying a different used set, getting them refurbed and then swapping them over.

I have the 17" out of the factory but I like the look of the 18" which can be picked up on eBay for a reasonable amount.

Are these a straight swap? The overall tyre diameter is almost identical (due to the reduced sidewall size) so no worries there. 

I think though that the offset is different (56 Vs 54) - can anyone confirm? As I understand it the 18" will stick out a little more as presumably the sporty models have a slightly wider stance. Is this an issue? Does anyone know in real terms how much wider 54 will be over 56 on the same width wheel?

Thanks!

Edited December 28, 20223 yr by Buckers