I would probably stay away from a 35 or 40 profile and go back to a 45, if you looking to protect your rims from potholes.
Maybe 245/45/18
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I like the goodyear F1. You can rotate them in a traditional manner. A lot of tires for BMW's are directional, and they dont last as long, as a result. Goodyear F1's are asymmetrical, which means you can cross the right rear to the left front and bring the left front down to the left rear and vice versa.
Also, in Chicago, much like in Michigan, these tires will be much better than a Michelin pilot sport 3 in November and March/April when you snow tires are not on the car.
The treadwear is 560. You should get 50,000 miles out of these tires pretty easily, as long as you rotate them every 6,000 miles religiously.