Hi badbobby (have seen you on alpina forum), I have a set for mine. Got some BMW OEM 103's off ebay ( they could do with a refurb though) and sourced some Hankook Icebear from camskill (there was an offer on!).
You can't go any smaller than 17inch rims due to the brakes. I went for 225 45 R17's all 'round.
by the time I'd got them all sorted, the snow had gone!! So they're ready for next winter.