The transfer case, in turn, manages power distribution to the wheels. In normal dry-road operation, all the power goes to the rear wheels. Three exceptions are Subaru, Honda, and Volvo models that are normally front-wheel driven. Honda's CR-V system is purely mechanical, with no electronic control. The Volvo V70 XC uses a viscous coupling to energize the rear wheels.
Engagement is usually so progressive that passengers notice nothing but continued forward progress.
While on-demand mechanical systems are somewhat simpler than the hardware they replace, the addition of electronic controls means that this new approach generally does not save cost. On-demand 4WD can also be presented to SUV customers in various ways. Ford prefers a multimode approach, with knob positions for 2WD, on-demand 4WD, 4WD, and 4WD with low range. Here, the driveline is permanently engaged. Wheel-speed sensors alert a computer when traction is a concern.