All Wheel Drive is the cornerstone of every Subaru. But why it works so well is a function of the design of every Subaru. The symmetrical design of all Subaru models and the layout of their major mechanical components aids in their dynamic performance. The weight of a Subaru's mechanical parts is evenly distributed on both sides of the vehicle's centre line.

This promotes consistent handling and road holding whether the vehicle is turning to the left or right. The only weighted variable in any Subaru are the occupants in the cabin and there is nothing Subaru's engineers in Japan can do about that!

With its 'boxer' flat-four cylinder, horizontally opposed motor placed in the middle of the engine bay the weight is evenly distributed, unlike vehicles with transversely mounted motors, which have more weight on one side of the engine bay.

The 'boxer' motor - so named because the horizontally opposed cylinders have pistons moving from side to side mimicking the action of two boxers trading punches - also provides a lower mass in the engine bay, resulting in a lower and more stable centre of gravity.

Directly behind the Subaru motor is the longitudinally mounted transmission, again in the middle of the vehicle. The main propeller shaft takes power from the rear of the transmission down the centre line of the vehicle to the rear differential.

Then two equal length drive shafts feed the power to the rear wheels. Equal length drive shafts take power directly from the transmission to the front wheels.

Many other four wheel drive vehicles have the main propeller shaft off-set to one side to take power forward to the front differential as it can not be passed directly through the engine's sump. The result is unequal length drive shafts and unequally distributed weight.
A Subaru's symmetrical mechanical layout creates a better-balanced vehicle with higher and more consistent levels of handling, road holding and stability.

This results in higher levels of active safety - the ability of a vehicle to avoid an emergency or accident situation in the first place. The driver has a greater level of control of a symmetrically laid out vehicle and there are advantages in comfort.

This symmetrical layout of the major components is exactly the same in the Forester, Impreza, Legacy and Outback. The engineering philosophy is applied equally to all Subarus.

And of course the power is going to all four wheels all the time, unlike part time four wheel drive systems, which either have to be selected or are only activated electronically when sensors detect a wheel spinning, slipping or sliding. By then the vehicle's safety and that of the occupants might already have been compromised.

With a viscous centre differential, all manual transmission Subarus distribute the power to where it is most needed and can be used in the most effective way.

The Subaru All Wheel Drive system detects if the front wheels are spinning and feeds more power to the rear wheels, or vice versa.

Under hard acceleration or going uphill, more power is fed to the rear wheels because of the weight transfer to the rear of the vehicle. Going downhill or under braking, more power is supplied to the front wheels due to the weight transfer to the front of the vehicle.

The high performance Impreza WRX and STi models also have limited slip rear differentials to divide the power between both rear wheels more accurately for higher levels of traction and handling.

Subaru's All Wheel Drive works best due to its symmetrical layout. Rear wheel drive vehicles with in-line engines have a symmetrical layout but can not function as well without All Wheel Drive, which, as already noted, does not work as effectively unless it has a symmetrical layout.

Symmetrical All Wheel Drive is the best engineering and dynamic solution, they go hand in glove.