Apparently certain 18s on Mazdas can crack on severe potholes. I saw a newer 3 at my dealership with a wheel bent in at 90º and that's what I pictured every time I went over railroad tracks or big craters. The switch to 16s makes me much less paranoid! Plus, as I mentioned, it makes a world of difference to the car's refinement. I'm no longer irritated by the ride, and the steering is much more pleasant.