They are the same diameter as original 195/70s and have about 1" wider tread. Plus they are Michelins: round and well-made. This is probably the most cost-effective approach, unless you can find some good used stuff. Another approach are the TRX wheels and tires found on the 85-89 635s and 85-87 735s. They should be dirt cheap used (but you do not want to buy the tires new!) and work quite well on dry pavement. They also look pretty good on E9 coupes. Another OEM approach would be the 15x7 wheels found on the 88-92 (roughly) 525s and 735s. I think 215/60x15s are probably about the right diameter (no bigger) and there is a good selection of tires in this size.