My Z4 has a set of staggered 18" runflat tires, probably Bridgestone Potenzas, but I forgot to look while I was in Munich. They will have less than 10 miles on them when I take redelivery in a few weeks.
Sizes: Front 225-40-18
Rear 255-35-18
These tires sell for about $1300 at TireRack. If I can get close to what I need for a set of decent all season tires I may be willing to sell them. Please contact me if you are interested. PM or email: rmorinATwvdsl.net.