What Does Variable Steering Ratio Mean?
2 Answers
Variable steering ratio refers to the adjustment of the steering gear ratio based on the vehicle's speed and steering angle. When the car is in a parked state, moving at low speeds, or making large steering angles, a smaller steering gear ratio is provided. Conversely, when the car is traveling at high speeds or making small steering angles, a larger steering gear ratio is provided to enhance the stability of the vehicle's steering. BMW refers to the variable steering ratio as the "Active Steering System," which utilizes an electronic variable steering ratio system. The core of this system is a planetary gear set integrated into the steering column. An electric motor within the assembly adjusts the front wheel steering angle proportionally based on the vehicle's current speed. At low speeds, such as when navigating winding mountain roads, the active steering system increases the steering angle, allowing the front wheels to respond immediately to small steering wheel movements. This ensures the driver can maneuver through tight spaces without needing to turn the steering wheel multiple times.
Variable steering ratio refers to a design where the proportional relationship between the steering wheel's rotation amplitude and the actual turning angle of the wheels can vary. I experience this most during my daily highway commute. In regular cars, a fixed steering wheel angle corresponds to a fixed turning amount, but cars with variable steering ratio allow the wheels to turn significantly with minimal steering wheel movement at low speeds, making parallel parking particularly effortless. At high speeds, it shifts to slight steering adjustments for fine-tuning direction, providing exceptional stability. This technology primarily relies on electronic systems controlling the gear structure inside the steering mechanism to achieve these variations, much like BMW's Active Steering system, which can reduce the turning radius by over a full meter. Once accustomed to this steering, driving a regular car feels cumbersome, especially when maneuvering into parking spaces, as the steering wheel requires multiple turns.
