Do you know the Difference between AWD and 4WD? Don’t worry, this is actually a very common question. You’re not alone in wanting to know the answer.
The confusion about AWD vs 4WD is understandable. Before the 1980’s both terms were used interchangeably. It seems logical, a 4 wheel drive vehicle (if it has 4 wheels), would obviously also be an all-wheel drive vehicle. Before commercially available AWD vehicles were commonplace, the term all-wheel drive referred to vehicles that had more than 4-wheels, and all of these wheels received power from the transmission, for example, a 6-wheel drive vehicle. These days, it’s not as simple.
Difference Between AWD & 4WD
Today, there is a clear distinction between four wheel drive and all-wheel drive. This really has to do with the way the power is transferred to the driving wheels. The difference between AWD and 4WD is that a 4WD transmission sends equal power to both the front and rear axles. An AWD vehicle shifts power between the axles as needed. That’s the basic definition. If the difference between AWD and 4WD is exactly clear yet, fear not. I’ll provide a detailed technical description of each transmission type and how they work. I’ll also offer the pros and cons of 4WD vs AWD and talk about how this technology came to be.
VIDEO | 4X4 VS AWD : What’s the Difference?
Four Wheel Drive
Four wheel drive, 4WD, and 4 X 4 are terms used to describe the same type of vehicle. The latter (4 X 4) is probably the most common, and it most accurately describes the function. The term 4 X 4 means 4 wheels and 4 drive wheels. It can similarly describe any type of vehicle: 4 X 2 is a vehicle that has 4 wheels, with 2 driving wheels; 6 X 4 has six wheels, of which 4 are driving wheels. I think you get the picture.
From this, it’s clear that a vehicle can have any number of driving axles. These are axles that transmit engine power to the wheels. A four wheel drive vehicle has a standard transmission, with gears like any other car. The difference is that 4WD utilizes a transfer case. This is an auxiliary gearbox attached to the standard transmission system.
On a regular rear wheel drive car or truck, the final drive gear is connected directly to the prop shaft which sends power to the rear differential. The differential then sends the required torque to each of the rear wheels. A regular front wheel car has a differential at the transmission that connects through constant velocity (CV) joints to the front wheels. A 4WD does both these tasks, using the transfer case.
The transfer case allows the driver to select either 2 wheel drive or 4 wheel drive by means of a gear shift or a switch. An electrically operated 4WD simply uses a servo to engage the 4WD mode when it is powered. Inside the transfer case, gears either transfer power to the rear prop shaft or both, depending on the driver’s selection.
In most cases, a 4WD transfer case will also include a high-ratio / low-ratio gear. This will be indicated on the transfer selector inside the vehicle as 2H, 2L, 4H, and 4L. Though, not all 4 X 4 vehicles have a 2L selector. When selecting 2H or 4H, the driver is choosing to operate the final drive gear at the normal driving ratio. The selection of 2 or 4, is the decision to use 2 or 4 wheel drive. The high ratio (2H or 4H) is used for most driving conditions. When extra torque is needed, like when the vehicle gets stuck in heavy mud, sand, or snow, the driver has the option to engage a low ratio final gear. Because this is usually used in conjunction with 4WD, most 4X4 vehicles only have the option for 4L. This means the driver is selecting four wheel drive with a low-ratio final drive. This increases the torque transmitted by the transfer case. The vehicle will have a very low speed but an exponential increase in the torque sent to the axels. The wheels spin slowly but are able to move the vehicle through heavy resistance.
It is important to note that 4WD cannot be used on paved roads. Because the front wheels are closer to the transfer case, more power is transmitted to these wheels. In off road conditions, this is not too serious because the torque demand is constantly shifting between the rear and front wheels. However, on a hard surface, like a paved road, the torque demand remains constant. This means there’s a tendency for the front wheels to want to move faster. This is not possible because there is no traction loss at either side of the vehicle. On loose dirt, wheels spin more readily.
The torque difference between front and rear power transmission results in a phenomenon known as transmission wind-up. The extra torque transmitted to the front wheels is absorbed by the transfer gears, causing them to lock into one another. This makes it difficult to disengage 4 wheel drive and harms the transfer case.
All-wheel drive vehicles use a third differential to transfer power between the front and back axles. This means that the driver does not select a constant 2 or 4 wheel drive mode. Instead, the differential in the transfer case shifts power between the front and back axles, depending on which has the least torque.
The differential was first developed to shift power between the left and right wheels, depending on which was moving faster. This was mainly for cornering, when the outer wheels cover a greater distance and, therefore, need to move faster to prevent the vehicle from skidding. A differential at the transmission works on the same principle. Though, instead of transferring torque to the wheel that needs it most, a transmission differential transfers torque to the axel that needs it most.
This means that there is a constant shifting of power between the front and rear wheels. If the front wheels start to spin faster, more power is transferred to the rear wheels and vice versa. At no time is equal power transmitted to the front and rear axles. The purpose of an AWD transmission is to provide the best traction and is most advantageous on wet, or snow-covered roads, where traction can be lost at any of the wheels without notice.
Most modern all-wheel drive vehicles us electronic components, controlled by the onboard computer. This allows the transmission to work with the brake-assisted traction control to ensure the maximum traction to every wheel. The computer makes fines adjustments to the power transmitted to each wheel many times per second. The driver does not need as much skill to control a skid when driving an AWD vehicle.
AWD vs 4WD Pros and Cons
- The driver has control when to engage 4WD
- Equal power is transmitted to both the front and rear wheels, resulting in the best power delivery for adverse conditions.
- 4 X 4 is the best for off road driving because of the constant power distribution to all 4 wheels and the option to engage low range (low ratio final drive).
- Driver needs a degree of skill, as 4WD needs to be manually engaged.
- Cannot be used permanently on hard road surfaces.
- Automatically transfers power to all four wheels and requires no additional driver skills.
- Can be used on any type of road surface
- Does provide maximum traction in adverse conditions.
- More expensive and transmission repairs cost more.
All-Wheel Drive / 4-Wheel Drive Combination
Many top SUV models provide the best of both. This is an AWD system that can also supply power to all 4 wheels permanently. By locking the transmission differential, equal power is sent to both the front and rear axles. This allows the an AWD vehicle to function in then same way as a traditional 4 X 4. Like a conventional transfer case, when an AWD differential is in 4WD mode (by locking the transmission differential) it cannot be used on high traction surfaces, like paved roads. When the diff is not locked, it drives like any other AWD vehicle on any type of road surface.
Although Jeep Quadra-Trac (introduced in 1973) is generally credited as being the first AWD transmission with off-road capabilities, this is incorrect. Land Rover was the first to introduce a transmission differential with a “Diff-Loc”. The Land Rover 101 was a revolutionary vehicle. I know this because I had the good fortune of driving one halfway across Africa. It is one of my personal favorite 4 wheel drive vehicles of all time.
The Land Rover 101 was commissioned by the British army in the 1967 as a go anywhere 4 wheel drive vehicle. Apart from the all-aluminum V8 engine, transmission, and body, this vehicle was the first to use a locking transmission differential. The combination of power, incredibly lightweight design, and the most advanced transmission for it’s time, made the 101 the best 4 X 4 for decades to follow. It was produced exclusively for the British military and NATO between 1972 and 1978. Eventually being decommissioned in 1991 after the Gulf War.
When the first Range Rover came to be in 1972, it used the Land Rover 101 chassis, engine and transmission. The Range Rover was, therefore, the first production vehicle to use a locking transmission differential, making it the first off-road AWD vehicle. Modern Range Rovers, Land Rovers, and many other off-road SUVs use the same system to this day.
4WD and AWD History
The origins of both 4WD and AWD is debatable, not many agree as to who invented 4WD, never mind AWD. Though the general consensus is that the first 4WD vehicle was invented by Ferdinand Porsche in 1899. It was publicly displayed for the first time at the 1900 Paris World Exhibition. This was not only the first 4WD, but also the first AWD, and the first electric car. Four electric motors were used, one at each wheel, powered by batteries. However, this car never went into production. The concept of independent electric motors at each wheel is used to this day for specialized, heavy-duty, construction and mining vehicles, as well space rovers, like the “moon-buggy”. Though, the correct modern term for these vehicles Individual Wheel Drive (IWD).
During the early 1900s, several 4WD vehicles were built in limited numbers for motor racing. The first of these was a Dutch car named Spyker. It was built specifically for the 1903 Paris to Madrid race. Bentley also manufactured several 4 wheel drive racing cars around this time.
The American Four Wheel Drive Auto Company (established in 1908) was the first motor manufacturer to mass produce 4WD vehicles. The 3-Ton American Four Wheel Drive Model B and the Jeffery / Nash Quad 2-ton were the first US military 4WD trucks from 1913 – 1919. They were used during World War I.
In 1926, Mercedes-Benz introduced the G4, which was the most sophisticated 4WD vehicle for it’s time. This became the standard for all four wheel drive vehicles that followed. The first Japanese 4 X 4 (Kurogane Type 95) went into production in 1937. Mercedes Benz was the first auto-maker to manufacture a permanent four wheel drive, or AWD vehicle. The Mercedes Benz G5 used a third differential to distribute power from the transmission. This is still the method used for modern AWD vehicles. Production of the Mercedes Benz G5 started in 1937. The BMW 325 4 X 4 went into production during the same year and also featured a transmission differential, offering permanent 4WD. Both these vehicles also used fully independent suspension, which was not common at the time. This resulted in a comfortable four wheel drive passenger car, not that different to modern AWD equivalents.
World War II is considered the birth of the 4WD as a popular vehicle. Most notably the Jeep, which was manufactured during WWII by both Willys and Ford. The Willys Jeep, which became the basis for the Jeep Wrangler is seen by most as the 4 X 4 that made this vehicle type famous. In the years that followed WWII, civilian four wheel drive vehicles began to make an appearance. Before this time, 4WD was reserved for specialized military vehicles. In 1945, the WWII (Willys) Jeep was sold commercially. Shortly after this, in 1948, Land Rover started production on the Series I Land Rover. In 1960, Toyota introduced the FJ40. This was the original version of the modern-day FJ40 Cruiser.
Through the 1970’s 4WD and AWD SUVs and trucks grew in popularity. This was probably most prolific in the US, with a wide variety of Jeep 4WD and AWD vehicles being made available. Ford, Dodge, and Chevrolet had their own versions. Though the Jeep Cherokee was the vehicle that made the family four wheel drive vehicle a common feature on and off the road. The British equivalent, the Range Rover, was more luxurious, and considered by many (including myself) a more capable off-roader. However, the Range Rover has always been much more expensive. The Jeep Cherokee remains one of the most popular AWD SUVs.
Before 1979, both 4WD and AWD were seen as off road vehicles that could be used on the road. There was no distinction between AWD and 4WD, they were all considered to be 4WD vehicles that that could traverse harsh terrain. Though, both the Jeep Cherokee and Range Rover were, in fact AWD vehicles. The scenario changed when Audi introduced the legendary Audi Quatro. This was to be the first high-performance AWD passenger vehicle. The Quatro was not designed for off-road use, it looked much like any other sedan of the time with a low ground clearance. For the decade that followed, the Audi Quatro went on to dominate the European rally championships.
Because of the motor sport success of the Audi Quatro, other vehicle manufacturers started following this example. Subaru and Lancia, who were both major competitors on the European Rally scene, designed their own AWD sedans. Through the 1980’s the shift from 4WD as an off road vehicle to AWD family sedans and high performance vehicles required a paradigm shift. With this change, the difference between AWD and 4WD needed to be clearly defined. This resulted in the modern definition as an AWD vehicle being a four wheel drive road vehicle, and a 4WD vehicle being an on-off road vehicle.
The final step in the evolution of the AWD vehicle, was the introduction of the Porsche 959 in 1986. This was the first super car to utilize AWD technology and remained in production until 1993. Today, AWD variants are available in every type of format. While the SUV and crossover vehicle market is probably the biggest for AWD vehicles. Compact, mid-size, and large sedans are available in AWD, as well as many high-performance sports cars.
The main advantage of using AWD for on-road vehicles is superior handling, better cornering and, most importantly, better traction on slippery roads. The proven safety record of AWD vehicles is what makes them popular as family sedans and SUVs. Modern 4WD trucks are used mostly for their utility value and off-road enthusiasts. SUVs that use 4WD, instead of AWD technology, are basically cheaper versions of the AWD equivalents. Here we need to make a clear distinction between AWD SUVs with a transmission Diff lock and those that use a conventional transfer case, requiring the driver to engage and disengage 4WD manually. The latter being the cheaper option, with AWD/4WD SUVs being the most expensive all-round.