Group 1: Importance of Four-Wheel Drive (4WD) - Four-wheel drive systems enhance vehicle stability and control, especially in slippery or winding road conditions, reducing the risk of understeer and oversteer [2][4] - Vehicles with 4WD can distribute power to all four wheels, improving handling and traction, particularly in extreme conditions [4] Group 2: Types of Four-Wheel Drive Systems - Four-wheel drive systems can be categorized into part-time, full-time, and on-demand systems, each with distinct operational characteristics [5][9] - Part-time 4WD requires manual selection and is commonly found in off-road SUVs, balancing power and fuel efficiency [7] - Full-time 4WD operates continuously, providing consistent traction but may have lower fuel efficiency due to constant engagement [9] - On-demand 4WD automatically switches between two-wheel and four-wheel drive based on road conditions, optimizing fuel economy while maintaining traction [9] Group 3: Specific 4WD Systems from Major Brands - Audi's quattro system has evolved from a manual locking mechanism to a more sophisticated quattro ultra system, which allows for dynamic switching between 4WD and front-wheel drive, enhancing fuel efficiency [12][24] - BMW's xDrive system utilizes an electronically controlled multi-plate clutch for power distribution, allowing for up to 100% power transfer to either axle, but may struggle in extreme off-road conditions [27][29] - Mercedes-Benz's 4MATIC varies across models, with entry-level systems using on-demand 4WD and higher-end models employing full-time systems with advanced torque distribution capabilities [30][32]