What’s the difference between front wheel drive, rear wheel drive, 4WD and AWD?

Question

More specifically, what are the pros/cons of each? Why do some cars use one system over the others and which is “better”?

EDIT: Thanks everyone for the explanations. It’s been very useful.

In: 10

Answer 1

In front wheel drive, the power is sent to the front wheels. The wheels pull the car behind them and control the the direction, which means the direction of the power delivered and the intended direction of motion are the same. This means easier handling, which is why many passenger cars use this.

Rear wheel drive delivers power to the rear wheels. It’s better for delivering more power from the wheels to the road. If you loom at a car from the side, when the wheels rotate one way, the rest of the car attempts to rotate the other way (action and reaction). This means the fron of the car tries to lift and the rear to slump. In a rear wheel drive, there’s a lot of weight in front to try to rotate, counteracting this effect. This means more force onto the road, which means better grip. Better grip means more torque and more power can be delivered to the wheels before they slip. But it also means the driven wheels are not the steering wheels, so the direction of motion snd direction of power delivery are not the same. This makes handling more difficult, and why people keep crashing sports cars.

All wheel drive drives both front and rear wheels, so it’s sort of best of both worlds, but adds weight to the car, so it’s mostly used in cars which are already bigger and heavier, so they need the help with power delivery AND handling.

4 wheel drive is like all wheel drive, but with one difference: all previous drives use differentials, which allow wheels to spin at different speeds. But it also means that in rough terrain, you get a situation where one wheel goes off the ground and is free to spin, meaning the other wheel gets no power. That’s how people get stuck in mud on the side of the road. In 4WD, the differentials are locked. All wheels spin exactly the same, and get equal power. This means that no matter the terrain, the wheel touching the ground always delivers power. But this is also really bad for driving on paved roads, as you want wheels to spin differently when turning around corners, and preventing that is actually detrimental to handling and causes excessive tire wear.

So AWD – roads and mild off-roading. 4WD – heavy duty off-roading and heavy lifting.