Symmetrical AWD, comprising of a longitudinally mounted Horizontally-Opposed SUBARU BOXER engine and a symmetrically designed 4WD drivetrain, is the system that Subaru has focused on for the best stability, safety and on-road performance. This unique drivetrain has been at the core of Subaru development ever since the world’s first 4WD passenger car was released more than five decades ago. The entire drive system, from the longitudinally mounted Horizontally-Opposed Engine to the rear differential, is mounted in a straight, symmetrical line. The characteristics of the longitudinally mounted Horizontally-Opposed Engine, which can be positioned low in the vehicle, have been maximised to bring the centre of gravity as low as possible, and towards the centre of the vehicle itself. The extreme performance that this superior weight balance provides works with the outstanding traction of 4WD to limit the chassis rolling and pitching, which occur driving around corners or braking, for maximum stability at all times. The resulting chassis rocks less and ride comfort is increased, making the journey enjoyable for all passengers.
Subaru’s Symmetrical AWD comes in a variety of different systems depending on the vehicle type and the transmission used.
Effects of the drivetrain on drivability
In FWD and RWD drivetrains that do not power all four wheels in the way that AWD does, excessive loads can be applied to the driving wheels. Lateral forces then come into play when cornering, and a lack of traction can cause the vehicle to abruptly change direction towards the outer side of the driving wheels. On the other hand, AWD systems distribute power between all four tyres in a balanced manner. This creates the most neutral handling possible, as there is no loss of grip in the direction that the vehicle is travelling, even if the vehicle is cornering. If one wheel starts to lose traction on slippery road surfaces, the other three driving wheels can provide the required traction to compensate. Compared to FWD and RWD systems, there is a much greater level of traction, and therefore safety. At the same power levels, acceleration is also so much better when there are four drive wheels rather than two.
Complementing this is the Symmetrical AWD that is only available from Subaru, allowing the entire system to be mounted lower in the vehicle. A low centre of gravity is directly related to more stable vehicle behaviour when cornering. These Symmetrical AWD characteristics ensure more stable driving under a range of different driving conditions, letting the driver drive with greater peace of mind. This unique layout is simply miles ahead of others in terms of on-road stability, whether that be on local streets or the expressway, or varying levels of rough terrain. “The driver no longer needs to worry too much about driving, and does not become tired so easily”. This is also an important safety aspect for preventing accidents before they happen.
An AWD system developed exclusively for 4-speed automatic transmission, E-4AT (with manual mode) and Lineartronic models to maximise the reliable driving performance of AWD models under any driving conditions. The Lineartronic CVT (Continuous Variable Transmission) uses a chain instead of a belt—allowing a greater span of overall ratios for improved performance and efficiency as well as a faster response to throttle input. The active torque-split AWD system usually distributes torque 60:40 front and rear, however sensors constantly monitor the vehicle's condition in areas such as changes in grip of the front and rear tyres or vehicle speed. The electronically controlled MP-T (Multi Plate Transfer) adjusts torque distribution to the front and rear tyres in real-time to suit driving conditions, as well as the transmission and driver inputs. This further increases the stability of the AWD system to deliver a safe and agile driving experience.
Variable torque distribution AWD
An AWD system designed exclusively for 5-speed automatic transmission, E-5AT (with manual mode) models to provide aggressive, sporty driving with increased turning abilities all while retaining the fundamental driving stability offered by the Symmetrical AWD. An uneven 45:55 front and rear torque distribution has been set for the front and rear tyres. Sending greater torque to the rear wheels can reduce understeer, a trait that plagues 4WD vehicles, when cornering for smooth and agile handling. Torque distribution is controlled automatically up to an equal 50:50 front and rear to suit road surface conditions for both sporty driving and stability.
Viscous centre differential AWD
An AWD system for manual transmissions with a simple layout consisting of a centre differential and viscous LSD. A 50:50 front and rear torque distribution is set under normal conditions. This maximises traction and provides driving backed with stability. When the front or rear wheels slip and traction is lost, or the wheel speed differs between the front and rear axles, the viscous LSD maintains optimum torque distribution between the front and rear and distributes power to the wheels with the most traction. It links the flexible gear shifting of the manual transmission to deliver sporty driving that always maximises the available traction.