The original bushing is made of rubber: it filters impacts well, but 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 vagueness between the steering wheel and the wheels.

Polyurethane deforms much less: the connection becomes precise and repeatable, and the car responds at the same point every time. The trade-off is more road noise and vibrations in the cabin, especially when cold.