What Is Four Wheel Drive (4WD) | Diagram, Advantages and Disadvantages

• Front-wheel drives are those in which the front wheels of the vehicle are driven by the engine. It has a front-wheel drive with the engine in front of the front axle, driving the front wheels. Whereas, Rear wheel drive places the engine at the front of the vehicle and the driven wheels are located at the rear.

• The front wheels drive layout is chosen for its compact packaging. Rear-wheel drive makes it impossible to have a rear seat if the engine occupies the space.
• In front wheels drive engine cooling is good (radiator in front), and an electric fan can be fitted, whereas in rear-wheel drive high radiator performance is required because of forced air cooling.
• Front wheels drive is insensitive to side wind whereas rear-wheel drive is sensitive to side wind.
• In front-wheel drive, there is higher tire wear in front wheels, because the highly loaded front wheels are both steered and driven. In rear-wheel drive, there is uneven tire wear.
• In front-wheel drive, there is poor braking force distribution (nearly 75%to in the front and 25%to the rear)whereas there will be a good braking force distribution in rear-wheel drive.

Working of Four Wheels Drive:

• In four-wheel drive, there is a drive train that allows all four wheels to receive torque from the engine simultaneously and all the four wheels are driving.
• It uses a different that allows one input shaft, to drive two output shafts independently with different speeds.

• The differential distributes torque while distributing angular velocity such that the average for two output shafts is equal to that of the differential ring gear.
• Each powered axle requires a differential to distribute power between the left and the right sides.
• When all four wheels are driven, a third differential can be used to distribute power between the front and the rear axles.

Advantages of Four Wheel Drive:

• Traction is nearly doubled as compared to a two wheels drive.
• Handling characteristics in normal conditions can be configured to emulate front-wheel drive or rear-wheel drive or some mixture, even to switch between these behaviors according to circumstances.
• Even Tyre wear.
• More balanced axle load distribution.
• Reduced sensitivity to side wind.

Disadvantages of Four Wheel Drive:

• The weight of the vehicle is 6% to 10% higher.
• There is a 5% to 10%  increased fuel consumption.
• Smaller boot compared with front-wheel drive vehicles.
• There is a lack of ABS compatibility in some systems.