AWD: The five types of Subaru systems

Vehicle Dynamics Control (VDC) All-Wheel Drive:

The B9 Tribeca and the Outback 3.0L R VDC Limited model combine the VTD AWD system with Vehicle Dynamics Control (VDC) to help the driver maintain directional control and stability. Using a series of sensors throughout the vehicle to measure steering angle, yaw rate, individual wheel speeds and lateral (cornering) g-forces, the VDC system monitors vehicle stability and continuously compares it to the driver’s intended direction. If VDC detects instability, it applies corrective action to help restore control.

The VDC system helps keep the car going where the driver steers it, using individual wheel braking and throttle control to correct under-steer (front-wheel drift) or over-steer (rear-wheel drift). The four-wheel electronic traction control system (TCS) adds an extra margin of driving safety without impeding VTD AWD operation.

The VTD system can vary the power distribution as needed to respond to traction conditions. It adjusts the front/rear power split in the differential according to weight transfer under acceleration and deceleration (as indicated by throttle input), always sending more power to the wheels with the best traction.

The VDC system also incorporates an all-wheel, allspeed Traction Control System (TCS) to help reduce wheel spin. The combination of these two technologies helps provide outstanding handling and control in a wide variety of driving conditions. Controlled by VDC, the VTD center differential – not the traction control system – governs power distribution.

The system operates while driving in a straight line or cornering and can help maintain traction even if up to three wheels are slipping. If the driver is applying more throttle than available traction will allow, VDC will reduce engine power. It is important to point out that the VDC system uses traction control as a second line of defense, activated only when VTD alone cannot maintain sufficient traction.