The metric tire size? Don't bother. Get a set of newer wheels and get regular size tires ... anything off an e28, other e24s, e32 and e34s fits. Those tires are not very good (since they're still pretty much built to 80s standards by the few that make them), and they're jolly expensive (upwards of 200/a piece). For that money, you can get a nice used set of wheels and a set of tires, and still have money left over.