Plugging in your numbers above on willtheyfit.com yields the following: Front: 195/45-16 diameter is 556.5mm 175/55-13 diameter is 522.7mm Difference: 33.8mm, which equates to a 16.9mm lower ride height in the front on the 13s. Rear: 195/45-16 diameter is 556.5mm (again!) 205/55-13 diameter is 555.7mm Difference: 0.8mm, which equates to a 0.4mm lower ride height in the rear on the 13s. Ride height is easily adjusted with the collars on the dampers. You will want to specify your car to have the dampers to have the ride height adjusting collars (or whatever the trade name for these might be). When I went through this decision, I read posts with lots of opinions on either side. It seemed to me that generally, those who went with larger wheels (14", 15", 16") did so primarily for aesthetic reasons, and those who went with the smaller wheels (13") did so primarily for performance reasons. On my own 7, I have only ever known 13s, so my opinion will be of little value here. Best of luck, sir. -Sean