I'm going to be picking up my Z4 this week, and going to be changing out the RFTs... These are a set of OEM Bridgestone Potenza that comes standard on the M-Sport 18' wheels (style 325M)
Front: 225/40R18
Rear: 255/35R18
Will have about 1,000 miles on them, so essentially new. TireRack has the set of 4 for $1,275 + about $50-60 shipping. Will sell them for $900 shipped, so you save over $300... or $800 pick up. Or PM with best offer.
Will post pics up once I pick the car up.