Originally Posted by colson79
You could change to non-run flats without any issues but I wouldn't change the aspect ratio on the tires. All of the electronics systems like stability control are calibrated to a specific tires size so you could run into problems. In fact I read a post on one of these forums where some changes the tires/rim with a different size than recommended and he was getting chassis stabilization errors. The problem went away when he put the original tires back on.
Had a lengthy discussion with the folks at the Tire Rack they agree with BMW.CA you should not change the aspect ratio on 19" wheels. This would expose you to many potential problems. I take back what I said in my previous post.