Which all-wheel drive system is the best?

The term "all-wheel drive" is used to refer to various systems offered by several automobile manufacturers that differ in design and performance. So which one is best?

Jason Fenske of Engineering Explained tried to answer this question with a very good metric: "The best all-wheel drive system is the one that is least likely to get you stuck." That seems reasonable to us.

A prerequisite for a good all-wheel drive system, as Fenske notes, is a lockable differential. This allows torque to be transmitted only to the wheels that have traction. The wheels that have no traction are free to spin, and with an unlocked (commonly referred to as "open") differential, most of the torque follows the path of least resistance and is transferred to the spinning wheel. The trapped wheel will have much less torque, if any at all, and will be stuck.

Four-wheel drive systems include front and rear differentials that distribute torque to the wheels of each axle, and a center differential that controls the distribution of torque between the front and rear axles (on some vehicles, transfer cases perform essentially the same function)3. All three differentials can be locked to allow torque to be transferred to where it can be used.

Many vehicles are equipped with lockable differentials, but Fenske has focused his attention on the Jeep Wrangler, Ram 2500 Power Wagon, and Mercedes-Benz G-Class.

Note that although the video shows older versions of each of these vehicles, modern models use essentially the same all-wheel drive system. Therefore, the logic and reasoning used here remains valid.

Fenske considers the Mercedes system to be the best because it uses an inter-axle differential instead of a transfer case. In Jeep and Ram models, the driver can choose rear-wheel drive only or 50/50 torque distribution between the front and rear wheels; the G-Class, according to Fenske, offers more flexibility in torque distribution between individual wheels.

If you prefer all-wheel drive, such as Subaru or Audi, Engineering Explained also has a video of a better version.