A four-wheel drive system is one in which all four wheels of the vehicle are driven. Compared to two-wheel drive, all-wheel drive systems provide better propulsion on loose surfaces and better traction on slippery roads. Learn all about the function, components and maintenance of all-wheel drive now.

Function of all-wheel drives in passenger cars

All-wheel drive sends power from the engine to all four wheels of the car. The drive power is distributed between the front and rear axles in a predefined ratio. This provides advantages in unfavourable conditions such as wet roads. Particularly in combination with traction control, all-wheel drives provide better driving dynamics and increased traction on the road. Load change reactions such as understeer or oversteer in curves are often significantly less with all-wheel drive than with drive from only one axle. In addition, all-wheel drive allows off-road vehicles to make much better progress on loose surfaces.

Advantages and disadvantages of cars with all-wheel drive

All types of all-wheel drive systems in cars offer advantages, but are also associated with disadvantages. The advantages include the equal distribution of drive power to the front and rear axles, and the associated driving characteristics. The disadvantages of all-wheel drive include the higher price of a car with all-wheel drive compared to the same vehicle with front-wheel drive or rear-wheel drive. Also, a four-wheel drive car is usually heavier, and fuel consumption increases due to mechanical drive losses. Driving both axles means that more components are needed, which in turn increases maintenance costs.

Components and drive variants for all-wheel drive

Compared to vehicles with pure rear-wheel drive or pure front-wheel drive, a car with 4 x 4 drive has a more complex powertrain structure. This is because additional components are needed to distribute the engine’s drive power to the front and rear of the vehicle.

• Transfer case between front and rear
• Coupling for the all-wheel drive
• Central differential in the drive train
• Cardan shaft for power transmission
• Drive shafts front and rear for additional drive of the axle

Depending on the vehicle model and type, all-wheel drive is implemented in different ways. If the vehicle engine is located at the front, its power is usually transmitted to the rear axle via a cardan shaft. The additionally driven wheels of the all-wheel drive usually receive their power via separate drive shafts. Often, a clutch is integrated into the drive train, which engages one of the axles only when necessary. Such a clutch is often controlled automatically. A central differential integrated between the axles compensates for differences and prevents tension in the driveline.

All-wheel drive for off-road vehicles and hybrid all-wheel drive

Particularly in off-road vehicles, manufacturers sometimes still use rigid axles whose differential can be locked via a differential lock. The same applies to the centre differential. Vehicle manufacturers use a completely different drive technology for hybrid all-wheel drive. Here, only the wheels on the front axle are driven directly via the combustion engine and the transmission. The wheels on the rear axle, on the other hand, have their own electric motor.

Permanent all-wheel drive or selectable all-wheel drive

All-wheel drives can be realised as permanent all-wheel drive or engageable all-wheel drive. If permanent all-wheel drive is installed as the drive type, the drive force can be transmitted to the wheels of all axles at any time. With the selectable variant, the driver or an automatic transmission can selectively activate or deactivate the all-wheel drive function for one axle.

Selectable all-wheel drive for off-road vehicles

An engageable all-wheel drive is often installed in off-road vehicles or pickups with all-wheel drive. These vehicles are driven by rear-wheel drive in normal driving mode. If required, the all-wheel drive can be activated by the driver or automatically by means of a switch or lever. Only then is the drive power transmitted to the front and rear axles together.

All-wheel drive for electric cars

Electric cars are also often offered with all-wheel drive. For this purpose, separate drives are installed for the front and rear axles of the electric vehicle. This drive variant therefore does not require any additional components, such as a transfer case or a central differential.

The motor at the front of the e-car drives the wheels on the front axle. The rear motor, on the other hand, transmits its power exclusively to the wheels on the rear axle. Some electric cars also have a separate drive motor for each of the wheels, or a motor for each of the two wheels on the rear axle.

Maintenance for cars with all-wheel drive – tips and tricks

There are a few things to keep in mind when maintaining cars with four-wheel drive. The more complex drivetrain requires a careful inspection, during which more parts need to be checked. This includes, for example, the cardan shaft or the transfer case.

Often a car with all-wheel drive has one differential per axle, as well as a central differential. In this context, the change intervals for the differential oil should be observed. Older off-road vehicles also often have points that have to be lubricated by hand, for example in the area of the front axle.

Check axle drive and wheels

Since all wheels are driven in four-wheel drive, there are also more parts to check in the wheel drive area. This includes the drive shafts on all-wheel drive vehicles with independent wheel suspension together with the associated axle boots.

The tyres of all-wheel drive vehicles are also subject to constant wear. Some manufacturers of all-wheel drive vehicles recommend that all four tyres be replaced when changing the tyres, as different diameters could damage the all-wheel drive.

What you need to consider when buying spare parts for four-wheel drive vehicles

More and more vehicles have four-wheel drive. This applies not only to off-road vehicles, but also to normal passenger cars. Even in SUVs, the presence of all-wheel drive is often no longer a question. Spare parts for vehicles with all-wheel drive are generally readily available. However, when selecting spare parts for cars with all-wheel drive, you must consider a few points.

This is because, as a rule, the parts for vehicles with all-wheel drive sometimes differ significantly from variants that are installed in models with only one driven wheel pair. This is of particular interest if a certain vehicle model is sold with both four-wheel drive and a driven axle.

To ensure that you select the correct spare part for your vehicle, you should compare the part number of the installed component with the replacement part. Photos of the part on offer also help to identify the right spare part. At Autoparts24, the search for suitable parts for the all-wheel drive is very easy thanks to the practical search function.

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