Introduction:
Front- or rear-wheel drive indicates on which wheels the engine’s driving forces are transmitted. Most car manufacturers opt for front-wheel drive. The engine provides the driving forces. With a manual gearbox, the gearbox is operated with the clutch, while with an automatic transmission this happens inside the transmission itself. Via the drive shafts, the power finally reaches the wheels.
Front-wheel drive:
With front-wheel drive, the front wheels are connected via the drive shafts to the gearbox (with an internal differential). The engine block is usually mounted transversely to save space. Car manufacturers often choose front-wheel drive. It is cheaper than rear- or four-wheel drive because fewer materials are used, and it is more space-saving and less susceptible to vibrations than rear-wheel drive.
Rear-wheel drive:
In cars with rear-wheel drive, the engine block is mounted longitudinally. From the gearbox, a propeller shaft (or intermediate shaft) runs under the car (positioned above the exhaust and out of sight) to the final drive.
High-powered cars with rear-wheel drive are often more prone to oversteer (the car takes a wider corner than necessary, the rear wants to overtake the front). A feature such as ASR is therefore no unnecessary luxury. Rear-wheel drive is used by manufacturers less frequently than front-wheel drive. Especially cars that have to deliver a lot of power (including BMW and Mercedes) are driven via the rear wheels. They also want an ideal weight distribution between the front and rear axles. By placing the engine in a longitudinal position, the gearbox is located under the center console in the interior. The gearbox is therefore positioned closer to the rear axle. The center of gravity is now shifted more towards the rear.
Another advantage is that in this way more power can be transferred to the road surface. When accelerating hard with a car that has more than 250 hp, the load on the rear wheels becomes much higher, just as the load on the front wheels increases when braking. During acceleration, the load therefore increases on the rear wheels, which makes the chance of wheel spin much lower than if the car were driven by the front wheels.
Cars with rear-wheel drive also have a specially shaped fuel tank, because the propeller shaft and final drive are mounted underneath it. A saddle tank with an additional jet (fuel) pump is then fitted.
Four-wheel drive:
In cars with four-wheel drive, as the name suggests, all four wheels are driven.
The advantage is that all engine power can be used to accelerate without wheels spinning, and that there is much more grip on unpaved roads. Off-road vehicles often have four-wheel drive, because with the aid of the ASR system sufficient power can usually be transmitted even on surfaces where a front- or rear-wheel driven car would get stuck (think of snow, sand or mud). Some high-performance sports cars are also equipped with four-wheel drive.
There are different systems, where there is no permanent drive on all four wheels simultaneously. Two different systems are described on this website, namely the Haldex clutch and a transfer case that is mounted to the gearbox.
Haldex clutch:
Used on VAG brands; VW, Audi, Seat and Skoda. The Haldex clutch is located at the rear axle and controls the drive forces from the propeller shaft to the drive shafts of the wheels. The front wheels are driven continuously.
Click here for more information about the Haldex clutch.
Transfer case:
Used on, among others, BMW. The transfer case is mounted to the gearbox and controls the drive forces to the front wheels.
The rear wheels here are directly connected to the gearbox and are always driven.
