Thinking about changing the standard 17s on my Siggy. For more 17s, I don't like the look of 18s/19s on a non lowered car and seeing as I still have to use my car to go fishing in and therefore drive up and down some rough tracks I'm not likely to get it lowered!

Can someone explain to me about offsets, what it means, what the offset is on a Vec/Sig, what other makes of wheels fit (other manufacturers or wheels that have been retrofitted to another marque but are now up for sale). Anything else I need to know about before I spend some £££?