Understanding All-Wheel Drive (AWD) and Four-Wheel Drive (4WD)
Saturday, October 5th, 2019
Just what is the difference? In a way, nothing really. Both cars drive four wheels. All-Wheel Drive (AWD) has become the popular terminology to describe cars that drive all four wheels all the time. Four-Wheel Drive (4WD) on the other hand is used to describe cars that drive all four wheels selectably. The primary elements affected by either system are the differentials; the parts responsible for transferring power to the wheels and allowing them to turn at different speeds while going around corners.
AWD cars are always on four-wheel drive; this means there is no engagement from the driver. The advantage is that you have all four wheels under power when the need for the system is abrupt. With momentum crucial in off-road driving, you do not have to lose any when on AWD.
There are mechanical and electrical AWD systems. The former uses mechanical front, central and rear differentials to send power to all four wheels. The electrical system uses sensors to actively send power to wheels depending on available traction.
4WD cars, on the other hand, are typically large Sport Utility Vehicles (SUVs) specially adapted for proper off-road driving. They often have matching ride-height. Locking the differentials can be done from inside the vehicle in some cars and outside in others. This makes them capable as power goes from the transmission to what is known as a transfer case. Then the maximum torque is divided among the front and rear axles using the transfer case.
When the transfer case splits power evenly, it ensures that each wheel turns at the same speed. The implication is that, for the vehicle to turn, it needs to slip the inside wheels, a trait that makes them good in low grip situations, but poor on-road, hence being selectable.
Both AWD and 4WD are additional options to two-wheel drive. The AWD has the potential to return worse fuel economy figures all factors constant, but would be the best choice for every day motoring. The 4WD is perfect for the adventurer who takes his craft seriously. Once you know your path home, you’ll know which one to pick