Driving On Rough Or Slippery Roads

WARNING: This page does not describe the selected car, but rather 12 other vehicles, including the 2014 Subaru XV Crosstrek, 2014 Subaru Impreza WRX, 2014 Subaru Impreza, 2013 Subaru XV Crosstrek, and 2013 Subaru Impreza. However, it is still accessible from the selected car via links, so may be relevant.

When front wheels are on a slippery surface
When the front wheels begin to spin, the resulting speed difference between the front and rear drive shafts causes the viscous coupling to generate significant amount of shear torque. As a result, the torque distributed to the rear wheels becomes much larger than that distributed to the spinning front wheels. The traction and driving stability are thus ensured on a rough or slippery road.

Fig 1: Center Differential Torque Flow Diagram (Driving On Rough Or Slippery Roads)

When rear wheels are on a slippery surface
When the vehicle is accelerated quickly from a standing start with the rear wheels on a slippery surface, the distribution of the vehicle weight on the front and rear wheels changes and the rear wheels start spinning. Due to the resulting speed difference between the front and rear drive shafts, the viscous coupling generates a significant amount of shear torque, now in the direction opposite to that generated when the front wheels are on a slippery surface. As a result, the torque distributed to the front wheels becomes much larger than that distributed to the rear wheels.

Fig 2: Center Differential Torque Flow Diagram (On Slippery Surface)