A 4×4 refers to any vehicle with four-wheel-drive capability. The two digits in this figure represent the total number of wheels on a vehicle and the number of axles that receive power from the engine. Meanwhile, 4WD is an abbreviated form of the term four-wheel drive.
Conversely, a 4×2 car has a two-wheel-drive system. That means that the torque power from the engine is sent to both wheels attached to a single axle only. Cars can either be front-wheel drive or rear-wheel drive, depending on which axle the powertrain is connected. In hindsight, a 2WD stands for a 4×2.
The difference between a 2WD and a 4WD vehicle is that the latter has two differentials. A differential is what transfers power from the engine to the axle. In the case of a 4×4 vehicle, its two differentials power both the front and rear wheels of the vehicle.
Full-Time or Part-Time
There are two types of vehicles with 4WD systems: full-time and part-time. The engine of a full-time 4WD provides power to both the front and rear axles. On the other hand, a part-time 4×4 SUV can either be a front-wheel drive (FWD) or rear-wheel drive (RWD). Four-wheel-drive vehicles run on their rear wheels most of the time. In this scenario, the torque power is distributed 50/50 on both the left and right rear wheels while the front axle moves freely. The front wheels will receive power only when the four-wheel-drive mode is activated, which gives both wheels traction.
4WD and the Different Differentials
For 4WD vehicles, there are three types of differentials that are crucial to the capability of a four-wheel-drive capability: open, locking, limited-slip differentials. Each of these features plays a vital role in every 4WD vehicle, regardless if the vehicle has full-time or part-time 4×4 configurations.
An open differential, or open diff, enables the wheels of a turning vehicle to rotate at different speeds. Because of this feature, a 4WD truck can turn smoothly to the right because the outer wheels (left) rotate faster than the inner wheels (right), which rotate at a slower rate.
The problem with this differential is that the engine sends power to the wheel that has lower traction, or path of least resistance. Therefore, when traversing terrains with a soft surface, such as mud or snow, a 4×4 can get stuck on it. This is where the locking differential comes in.
When the locking differential (locking diff) is engaged, the power is divided 50/50 to the two wheels. As a result, the single wheel with traction can push the 4×4 forward, taking the vehicle out of that tight spot. That’s the reason why locking differentials are limited to vehicles with off-roading capabilities, such as 4WD and AWD.
The activation of the locking differential can be done either via mechanical means. Most 4WDs however, especially modern SUVs and pickup trucks, are equipped with automated traction control systems, which make diff locking more efficient.
With the limited-slip differential (LSD), the engine sends most of the power to the wheels with the most traction. At the same time, it limits the power to the wheels with not enough traction, thus, preventing slips. For that matter, this type of differential is often called torque-sensing because of the way it operates. All 4WD vehicles have this feature, as do AWD, which is highly effective for cornering and off-roading.
How Is a 4WD Different from an AWD?
An AWD, or all-wheel-drive, sports the same mechanism with a 4WD. That’s because AWDs also have two differentials, each connected by a drive shaft. Like a full-time 4×4, an AWD vehicle provides more torque to each of the wheels.
Because of this, cars that are AWD-capable can drive across loose surfaces, such as snowy or muddy pavements and gravel. Apart from that, AWDs are equipped with LSD. Similar to a 4×4, the engine of an all-wheel-drive car distributes more torque power to the wheels with higher traction.
Locking Centre Differential
What makes the full-time 4WD distinct from the AWD drivetrain is the way the latter’s locking centre differential operates. This differential system, which is located inside the transfer case, enables the full-time 4×4 to send equal power to each wheel when engaged.
The AWD vehicle, on the other hand, will operate differently. The vehicle will distribute the same amount of power to two wheels, which is similar to how a part-time 4WD SUV or truck would typically work.
This feature is why the 4WD is the perfect vehicle for off-road travel. Despite the benefits of a locking centre differential, you’ll be wise not to use this on dry, paved roads, which often has higher traction. Otherwise, you might end up damaging the front and rear axles of your 4WD.
What Are the Pros and Cons of 4×4?
Power and traction are probably the first two things that come into mind when thinking of the 4WD. Both of these qualities can inspire wonder and amazement to anyone who sees a 4×4 traverse a seemingly impassable terrain with ease. These features, however, are just part of a 4×4’s benefits to a driver over, say, a 2WD, for example. The other advantages of the 4WD are as follows:
· A 4×4 is the ideal vehicle type for off-roading enthusiasts.
· 4WD vehicles enable motorists to drive across dangerous weather conditions, such as snow or mud.
- A 4×4 provides superior grip across any type of terrain.
- The added weight of a 4WD vehicle gives better traction even on muddy or rocky surfaces.
- Vehicles that are 4WD-capable can reduce the likelihood of getting stuck on treacherous terrain.
- Driving a 4×4 on any terrain gives you confidence and control.
- 4WD vehicles have effective cornering capabilities.
While driving a 4WD can be fun and exhilarating, you just cannot have both worlds with it. Some of the disadvantages of a 4×4 are as follows:
- The heavier the vehicle, the higher the fuel it will consume.
- A 4×4 is costlier to repair as compared to a car with a 2WD system.
- 4WDs can be difficult to manoeuvre in urban areas, such as in parking lots, among others.
- The powertrain can be prone to torsion if the driver is not careful.
- There’s a tendency for a 4×4 to spin out of control when the front and rear axles rotate at similar speeds.
Should You Get a 4×4?
As mentioned earlier, if you’re looking for a vehicle with superior off-road capabilities, a 4WD will always be a great option. If you are undecided on whether to purchase a full-time or part-time 4WD, that depends on how you will use it. While the full-time 4WD capability can be effective on extremely loose terrain, a part-time 4×4 is perfect for off-roading and paved areas.