What are Full-Time 4WD and On-Demand 4WD?
2 Answers
Full-Time 4WD and On-Demand 4WD are described in detail as follows: Full-Time 4WD: Full-Time 4WD means that the vehicle is driven by all four wheels independently at all times. It achieves this through a flexibly connected central differential, which then distributes the driving force to all four tires via independent front and rear axle differentials. Unlike purely mechanical differential locks, the differential in Full-Time 4WD can be either a viscous coupling or a multi-plate clutch type, but both allow for a speed difference between the front and rear wheels, as well as between the left and right wheels. Whether a vehicle has Full-Time 4WD entirely depends on the construction of the transfer case. As the core component that manages different driving states of the vehicle, the transfer case largely determines the overall performance of the vehicle. On-Demand 4WD: On-Demand 4WD refers to a drivetrain that switches to four-wheel drive only when necessary, while remaining in two-wheel drive under other conditions. The system automatically switches between two-wheel drive and four-wheel drive modes based on the driving conditions, without requiring manual intervention. On-Demand 4WD differs from Part-Time 4WD, which requires manual switching between two-wheel and four-wheel drive, and Full-Time 4WD, which operates in four-wheel drive under all conditions.
Having driven so many cars, I feel like full-time four-wheel drive is like equipping your car with all-weather anti-slip soles—all four wheels are always putting in effort, making it rock-solid in rain or snow. Here in the north where icy roads are common in winter, driving an Audi with its quattro full-time four-wheel drive gives me peace of mind; even the steering feels lighter. On the other hand, on-demand four-wheel drive is much smarter—it quietly uses front-wheel drive to save fuel and money under normal conditions, only engaging the rear wheels when you start slipping during a rainy turn. Once, while driving a Honda CR-V through a muddy pit, I distinctly heard the rear wheels 'click' into action, like having an experienced driver beside you giving the car a push. If you mostly drive in the city, on-demand four-wheel drive can save you 20-30% on fuel costs.
