4 x 4 vehicles are extremely diverse and the terminology used to describe the architecture and functions of these cars differ depending on manufacturer and market. Marketing may also play an important role when it comes to terms related to 4 x 4 vehicles, because manufacturers are looking to increase sales in the first place. If you are interesting in purchasing a 4 x 4 car, you are probably a bit confused by terms such as 4 x 4, AWD, 4WD, and IWD. In this article we’re looking to explain these four terms and make it easier for you to research cars and make the right decisions.
4 x 4
4 x 4 is the general term describing two-axled vehicles which can provide power to all wheel ends. 4 x 4 vehicles can be full-time (all four wheels are powered all the time) or on-demand (the driver or the vehicle switches to 4 x 4 if conditions require it). But why are they called 4 x 4? The first figure refers to the total number of wheels, while the second represents the number of wheels that are powered. Following the same principle, there are 4 x 2 vehicles (where energy is transmitted only to two axle-ends or wheels), and 6 x 4 vehicles (such vehicles have three axles, and two of them provide power to two wheel ends each).
4WD stands for “four wheel drive” and refers to vehicles having two axles that deliver power to four wheel ends. In some markets, this term can refer to cars optimized for off-road driving. Vehicles labelled as 4WD usually have a transfer case allowing the driver to switch between the 2WD and 4WD operating mode. For some cars, the transfer is performed automatically, when car sensors detect conditions requiring 4WD capabilities. Most times, 4WD is associated with SUVs – cars with truck based platforms and large wheels that can withstand difficult terrain.
A type of 4WD vehicle is the locked 4WD driveline – in these cars, there is a direct mechanical link between front and rear axles and there is no mechanism to create a difference in the number of rotations in each axle. When you’re turning a corner in this type of car, the radius of turn is different for the two axles, and the tyre on the axle with the smaller radius needs slippery ground surface to avoid stress on the driveline. If you make a turn with a 4WD car at a low speed and on dry ground, the car will stop and you’ll become “locked up” – this is why you need to use the 2WD mode in normal driving conditions.
AWD stands for “All-wheel drive” and at the present time it refers to permanent multiple-wheel drive, where a differential is placed between the front and rear drive shafts. Anti-slip technology is used in these vehicles, allowing differentials to spin at different speeds while still transferring power from one wheel to another with better traction. The engine’s power is sent on the path of least resistance or the wheel with the least grip. So, instead of choosing between two wheels, with an AWD system you look for the least resistance across all four wheels. To counteract this effect, the best AWD cars are equipped with a centre differential that directs torque away from the spinning wheel. Unlike locked 4WD, AWD systems can be used on most surfaces, but are not recommended for demanding off-road use. Furthermore, an AWD system is the one where the driver does not need to intervene to select drive to all four wheels – in AWD the four wheels receive torque all the time. The advantage of this type of system is that 4 x 4 is engaged well before you encounter a dangerous situation, which means you are safer and you don’t need to make the decision to change the car’s mode as a response to danger.
IWD or “Individual-wheel drive” is a new term, referring to electric vehicles where each wheel is driven by its own electric motor. Such vehicles are more similar to 4WD vehicles or vehicles equipped with control systems, like anti-skid and anti-lock braking system. IWD vehicles come with multiple advantages: avoiding mechanical systems and parts like the central gear box and the differentials, easy replacement of motors, and lower maintenance. In case one of the motors fails, the other motors are powerful enough to allow the driver to take the vehicle at the nearest repair centre.
The terminology surrounding 4 x 4 vehicles can be quite confusing, so it’s important to know what the difference between 4WD and AWD is before making a choice. Based on your driving experience and the kind of conditions you’re driving through most of the time, you will be able to choose the right vehicle for you.