2 WD is 2 wheel drive system. Corresponding to it is the "4 wheel drive" (as the name implies, all 4-wheels of a car can get driving force).

There are two situations for 2WD cars system: front-drive & rear-drive.

1) Front-wheel drive means that the front wheel of the car is the driving wheel. The advantages of the front-wheel-drive vehicle under the same displacement are the effective output of kinetic energy, low fuel consumption, strong power, small size, large interior space, lightweight, Compact structure, low failure rate, high driving speed, etc. Front-wheel drive vehicles are generally used in small cars that are expensive and require a lot of space.

2) Rear-wheel drive means that the rear wheel of the car is the driving wheel. The advantages of the rear-wheel-drive vehicle under the same displacement are good load-bearing, simple structure, convenient maintenance, good handling performance, etc. Therefore, rear-drive vehicles are generally used for large and medium-sized freight and passenger vehicles with large volumes and large cargo capacity.

The four-wheel safety system (4wd system) is to change the 2wd system driving force of the engine from the 2WD to the 4WD. The reason why the 4wd system is included in the active safety system is mainly that the 4wd system has better engine driving force application efficiency than 2wd, and achieves better tire traction and effective use of steering force.

In terms of safety, the 4wd system has a better application of tire traction and steering, resulting in good driving stability and tracking.

In addition, the 4wd system has more off-road features that 2wd does not have.

Part-time 4WD

This is a four-wheel-drive system that the driver can manually select between two-wheel drive and four-wheel drive. The driver can switch the two-wheel drive or four-wheel drive mode by turning on or off the transfer case according to the road conditions. This is also the most common driving mode for general off-road vehicles or four-wheel drive SUVs.

Full-time 4WD

This transmission system does not require the driver to choose and operate. The front and rear wheels always maintain the 4WD mode. The engine output torque is set at 50:50 on the front and rear wheels when driving so that the front and rear wheels maintain the same amount of torque. The full-time drive system has good driving control and driving track. With the full-time four-wheel-drive system, you can drive smoothly on paved roads. But its shortcomings are also obvious, that is, it consumes more fuel and is not economical enough. Moreover, the vehicle does not have any device to control the difference in tire speed. Once a tire leaves the ground, it will often stop you there and cannot move forward.

But now, with the development of technology, the problem of all-wheel drive has been solved. The application of the electronic differential lock enables the full-time 4WD off-road vehicle to brake on the suspended wheel when one wheel is suspended, so that the power can be transmitted to other wheels that are still in contact with the ground, thereby ensuring the power output.

Real-time 4WD

Vehicles with a timely drive system can be controlled by a computer to select a drive mode suitable for the current situation.

On normal roads, vehicles generally use the rear-wheel drive. In the event of a bad road or slipping of the driving wheels, the computer will automatically detect and immediately distribute the engine output torque to the two front wheels and naturally switch to the four-wheel-drive state.  The application is simpler than eliminating the driver’s judgment and manual operation. Its fuel economy has been greatly improved, and it can cope with roads and off-roads freely.