The original bushing is made of rubber: it filters well, but it deforms under load. When cornering or braking, the control arm moves by a few millimetres and the alignment changes during the manoeuvre - this is the slack between the steering wheel and the wheels.

Polyurethane deforms much less: the connection becomes precise and repeatable, and the car responds in the same place every time. In return, more road noise and vibrations enter the cabin, especially when cold.