Selectable four-wheel-drive is a common feature used on trucks that turns low-traction situations into a stress-free walk in the park. Most trucks even feature a four-wheel-drive "low" setting to put more torque down to the surface in tougher scenarios. But how does the system actually work?
Jason Fenske of put together a video laying out how exactly a four-wheel-drive system works, and how it distributes power from the transmission, to the transfer case, to the differentials, and ultimately, to the wheels.
Fenske then shows us an acceleration test comparing the 2WD Hi, 4WD Hi, and 4WD Lo settings in a Nissan Frontier Pro-4X to see which mode puts down the fastest 0-30 mph time. Unlike all-wheel-drive supercars that use the added traction to put down more power, the 4WD in this case actually makes acceleration slower thanks to drivetrain losses.
However, when Fenske puts the truck into 4WD Lo, acceleration drops significantly thanks to that extremely low gearing ratio. Watch for yourself.