On the rear, things get tricky. Wide rubber will either hit the guards, or the chassis/trailing arm/rear spring. Most people prefer to make their tyres wider on the inside to avoid flares. First thing you will hit is the trailing arms, but because of the shape of the trailing arm, larger diameter rims will actually clear the arm if you relocate the handbrake cable set-up. Smaller rims will not and require offset trailing arms. The next thing you start hitting is the end of the spring. Depending on the wheel size and how low the car is, the spring may go inside the rim, but it depends on a few things and the car needs to be sitting fairly high to make it happen. The other option is a shorter spring which keeps the ends further away from the tyre.
