4WD vs AWD: Clearing The Confusion

  • Feb 21, 2019

Have you ever come across a car with 4WD or AWD written on the back and wondered what was the difference? After all, a car usually has four wheels. So what was it that car manufacturers are trying to tell us by using different terminologies like 4WD and AWD? Aren’t all these systems essentially a 4x4 drivetrain setup? In one word, yes. However, both 4WD and AWD differ in their construction and implementation and are helpful in different scenarios. Well, let us dive into a history lesson first to find out how 4x4 systems originated and segregated into 4WD and AWD as we know them today.

The first renditions of a 4x4 system can be traced back to the late 1800s, more specifically 1893, when an English engineer who went by the name of Bramah Joseph Diplock patented a four-wheel drive system for steam-powered traction engines (a self-propelled steam engine used to carry heavy loads that were really popular in the mid-19th century). However, it was not until 1903 that the first vehicle to be powered by an internal combustion engine (ICE) employed a four-wheel drive system. It was developed by two brothers, Jacobus and Hendrik-Jan Spijker, of Amsterdam for the Paris to Madrid race of 1903. Also, it might be hard to believe but before the world had laid their eyes on the first ICE-powered vehicle with a four-wheel drive system, a man who went by the name of Ferdinand Porsche had already developed an electric vehicle in 1899, which featured a four-wheel drive system.

Cars with four-wheel drive systems entered into mass production by 1908 and throughout the 20th century, 4x4 systems kept seeing advancements. These were mainly due to military requirements as the armed forces required vehicles that could go over harsh terrain with relative ease. Back in those days, anything that had all four wheels driven by the engine was termed a four-wheel drive or all-wheel drive vehicle.

Up until 1966, 4x4 systems were limited to jeeps and trucks and were only meant to be used on terrains with low levels of traction, basically off-road. Using them on tarmac with the 4x4 system engaged could heavily damage the drivetrain. Why you ask? Well, back then typical four-wheel drive systems used a transfer case that split the power coming from the powertrain (engine and gearbox) between the front and rear axle. This locked the two axles together and all four wheels are only able to rotate at the same speed. This is fine when travelling in a straight line. However, when going around a corner, the front and rear and the inside and outside wheels all travel at different speeds. So when a vehicle equipped with a four-wheel drive was traversing a loose surface, the tyres could skid and stay on course. However, on a surface where the level of traction is high, that was not possible and this put reverse pressure on the mechanism inside the transfer case, in turn damaging it.

So what happened in 1966? Well, a British carmaker by the name of Jenson Motors introduced the Jensen FF. It was the first car which was equipped with a 4x4 system that could be used on tarmac without damaging the drivetrain. How did Jenson Motors manage such a feat? They used a master differential and two one-way clutches to distribute the power from the powertrain. This allowed the wheels to be able to rotate at different speeds, thus not damaging the drivetrain when going around a corner. It was not a very sophisticated system compared to today’s standards, but an ingenious solution nonetheless that paved the way for future engineers to develop more complex 4x4 systems. This was truly the point when 4x4 systems differentiated into 4WD and AWD.

While this is not a rule of thumb, nowadays 4WD systems are referred to as part-time 4x4 systems that are designed to run on surfaces with low levels of traction. AWD systems on the other hand are 4x4 systems that can be used on all kinds of surfaces, but are primarily built for use on the road. Part time four-wheel drive or 4WD systems primarily still use the basic technology that was invented a century ago. The powertrain sends the power to a transfer case that splits it between all four wheels that are locked to rotate at the same speed. One addition that has happened over time to this kind of a setup is the addition of a low range option. This allows the driver to access huge dollops of torque while moving at really slow speeds. It is made possible by adding a shorter gear ring in the transfer case. This is really helpful in tricky off-road conditions like steep inclines, declines and slippery surfaces.

Full time four-wheel drive or AWD systems have evolved at a much rapid rate as most manufacturers nowadays have developed their system which differ from one another. However, the basic principle in most is the same: Instead of a transfer case, an AWD system mostly uses a center differential with clutch packs that can split power between the front and rear axle in different ratios. The clutch packs allow the two axles to rotate at independent speeds. Differentials on the axles allow the wheels to move at different speeds. Typically, an all-wheel drive system does not come with a low range option. However, that is not a given and many SUVs that utilise AWD systems do get a low-range gearbox.

4WD or part time 4x4 systems are designed to be used off-road only. We have summed that much up till now. So what is the advantage of AWD systems and why do we need them? Well, AWD systems have a host of applications in vehicles. From getting a better launch from the start line of a race to going at around a corner, an AWD system is helping out all the time. New-age AWD systems also use torque-vectoring which allows them to send the most amount of power to a specific wheel, one which has the most amount of traction. There it is then. The difference between 4WD and AWD. While one specialises in increasing traction off-road, the primary use of the other is to increase traction on road. That, however, does not mean that AWD systems cannot be used off-road.


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