Subaru's all-wheel drive technology stands apart from other AWD and four-wheel drive (4WD) systems. Despite the potential for confusion, AWD and 4WD aren't the same thing: Many differences exist that put Subaru's system in a category all its own. Whether or not you ultimately find it to be superior will, however, be determined by a number of variables, including your own particular experiences with the system.
AWD and 4WD similarities
Both AWD and 4WD systems have power flowing from the engine through the transmission to a transfer case. The transfer case is responsible for channeling the power through the driveshafts to the front and rear differentials of your car. The differentials are what split the power between your two pairs of wheels (front and rear).
4WD systems use the transfer case to tell all your wheels to do the same thing, dividing the power up evenly and rotating at the same speed as one another. AWD systems allow the front and rear wheels to operate independently of one another, which can be helpful in getting you out of sticky situations--such as slippery pavement, particularly through turns.
Finally, most 4WD systems, even when in full 4WD mode, will still only be 2WD systems (front or rear, depending on your car) until the system detects slippage from one or more wheels. It's a reactive system rather than an active system.
Symmetrical All-Wheel Drive
Subaru's AWD system takes the concept a step further by being symmetrical. Far more than just a catchy bit of PR, Subaru's drivetrain layout is exactly what its name implies. Its longitudinally mounted Boxer engine is engineered as one big piece, not several small pieces put together as afterthoughts. The two sides of the drivetrain mirror each other, and with the engine's low center of gravity, create a more balanced weight distribution throughout the car. The biggest advantage of this is that the power flows directly and cleanly through the engine, transmission, transfer case and driveshafts--making it to your wheels with the least interference possible. Other AWD and 4WD systems require the power to flow through 90-degree angles. On paper, that may not seem like much, but every extra step that it takes to get power from your engine to your wheels costs you time, possibly power--and efficiency.
Full-Time AWD Versus Part-time 4WD
Many 4WD systems operate as 2WD most of the time (front or rear drive, depending on the vehicle), until the driver chooses to shift the car into 4WD mode. While this can, in theory, save wear and tear on the drivetrain, it's not really an advantage in a dangerous driving situation. By the time you have a problem, it may be too late to safely do anything about it. With full-time AWD, like Subaru's system, you may not even ever know you were close to having a problem while driving.
Active Safety Feature
Unlike airbags, which only come into play after an accident has already happened, Subaru's active AWD system is considered a driver-controlled safety feature.
- Photo Credit theotherkiwi: Picasaweb
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