The cars we have seen have 205/55R16 or 195/65R15 (24.7" and 25.0" over all diameter.) The 2 sizes you discuss 225/50R17 or 245/45R17 have 25.9" and 25.7" overall diameter. We don't recommend using tires with such a tall overall diameter. This will effect speedometer and odometer reading. It will also make the readings on the data computer (MPG, MPH, Range etc) inaccurate. Because of this, we have never tested and would never recommend the use of such tall overall diameters. We are focused on what works best for the US market and US customers. The sizes you recommend, while they might (not likely without modification to the car) fit, will not enhance the high performance characteristics of a BMW. As everyone uses their car differently, this may be the best application for your specific situation.

There are not exact answers when it comes to tires. Every driver has a different style, use, and conditions. In the case of BMW’s we tend to bias our recommendations towards performance. They are “The Ultimate Driving Machines”, aren’t they?

Tim