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The difference between rear-wheel drive and all-wheel drive

In a car, we see the 4 wheels turning and we can sometimes wonder which wheels are driving the others.

There are mainly 4 types of wheel transmissions for cars:

- traction (front-wheel drive or FWD)

- propulsion (real-wheel drive or RWD)

- all-wheel drive (four-wheel drive or 4WD)

- All-wheel drive (all-wheel drive or AWD)



We then wonder what their meanings are and the differences between them:


- Front wheel drive (front-wheel drive or FWD)

Front-wheel drive systems offer two advantages: they take up little space and reduce fuel consumption. That’s why most vans drive this way. They allow the various components - the engine, transmission, final drive gear, differential - to be compacted in one place, freeing up a lot of room for the vehicle's interior. Lighter models also consume less fuel.


-Rear drive (real-wheel drive or RWD)

This system transmits energy from the engine to the rear wheels. The front wheels steer the vehicle, but the rear wheels propel it. Especially vans are equipped with this system, since they need more rear power when carrying cargo. In general, heavier luxury vehicles also have this system to manage the extra weight.

Sports and racing cars also use this system for better traction when going at high speeds. However, it complicates city driving in rainy or snowy weather. Since the front wheels carry less weight than the rear wheels, there is a risk of the driver spinning. To remedy this problem, he can practice safe driving techniques, such as driving at low speed, turning without accelerating, and wearing winter tires.


- All-wheel drive (four-wheel drive or 4WD)

Four-wheel drive systems offer great benefits when the weather conditions are not ideal. They are ideal for driving in thick layers of snow or sand, on muddy paths and on roads covered with ice.

Note that four-wheel drive vehicles are propelled only by the rear wheels until the four-wheel drive system is activated (either automatically by the vehicle or manually by the driver with a button or lever). Once this function is engaged, the energy of the engine is distributed among the four wheels. This mode is not always of great help. In fact, its use in ideal conditions can seriously damage mechanical components and tires.


- All-wheel drive (all-wheel drive or AWD)

All-wheel drive is a good option for those who want better traction without having to worry about having to turn the system on or off. This is permanently engaged in most all-wheel drive vehicles. Sensors controlled by the on-board computer determine how much energy is needed in any weather condition. This process, called varying the torque vector, provides excellent handling at all times.

This system significantly weighs down the vehicle, which causes greater fuel consumption. While all-wheel drive can handle all types of weather, testing it on very rough terrain is not recommended.



Road holding for propulsion VS traction:


The handling characteristics of front-wheel drive and rear-wheel drive are different.


It is known that it is the driving wheels which tend to deviate from the desired trajectory, because the lateral drift of the tire increases when it is subjected to a tractive force, that is to say when its coefficient of adhesion with the ground decreases. So, when pulling into a corner too quickly, the front wheels tend to slip out of line, and under the effect of centrifugal force, the nose of the car comes out of the corner, which is understeer.

On a rear-wheel drive car, it is the rear of the car that tends to come out of the turn and the car will drift from the rear which can continue into a spin - this is the oversteer.

In the majority of cases, however, front-wheel drive cars have demonstrated superior handling qualities in the average use that can be made of a car. They are particularly effective on wet and slippery ground (snow, ice), as demonstrated in 1934 by the famous Citroën Traction.

In the majority of cases, however, the Citroën years in this type of manufacture. It has now become widespread among all manufacturers for small and medium-capacity, only a few brands remaining attached to propulsion for their most motorized cars. Being able to arrange the engine transversely at the front also pleaded in favor of this configuration.


Advantages :

The propulsion allows a better transmission of power to the ground. Increased driving pleasure and the ability to perform controlled skids, which is much more complicated with traction. The car's weight distribution is generally better as some elements at the front of a front-wheel drive are found at the rear.


Disadvantages:

Handling on the road and traction are less easy. The rear tires wear out faster than front-wheel drive. Transmission to the rear wheels requires a drive shaft which penalizes the passenger compartment in the central rear seat.

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