Low Speed Range

The variable steering-gear ratio of the Active Steering component reduces steering effort to approximately 2 turns of the steering wheel from lock to lock. In the low speed range up to approximately 37 mph, the variable steering-gear ratio for the front wheels is combined with a degree of opposite rear-wheel steer. The effect is to increase vehicle agility.

Fig 1: Identifying Conventional Steering System Variable Steering-Gear Ratio - Low Speed Range

Courtesy of BMW OF NORTH AMERICA, INC.

When the steering wheels of a vehicle are turned, it follows a curved path around what is called the momentary axis "M".

In the case of conventional vehicles, that momentary axis is positioned at a point along the extension of a line passing through the center of the rear wheels.

Active Steering intervention turns the rear wheels in the opposite direction at speeds up approximately 37 mph.

Fig 2: Identifying Integrated Active Steering Variable Steering-Gear Ratio - Low Speed Range

Courtesy of BMW OF NORTH AMERICA, INC.

The consequence of the rear-wheel steering intervention is that the axis of rotation moves closer to the center of the vehicle with the same amount of steering effort.

In terms of agility and dynamic handling, that is equivalent to a vehicle with a shorter wheelbase.