The bar connects the two strut mounts. In a hard corner, the loaded suspension side pushes outward and the geometry deteriorates at exactly the moment when it is needed most: the bar distributes the load between both sides.

The front end feels more precise when turning in, and the car maintains the same response from one corner to the next. The effect is clear on older chassis, convertibles, and high-mileage cars; it is more subtle on a modern body that is already rigid.