Drivetrain Systems Explained: Difference Between FWD, RWD, AWD and 4WD

We explain the differences between front wheel drive, rear wheel drive, all wheel drive and four wheel drive, to help our readers make an informed choice or to understand their car better.

By Stephen

A Drivetrain is a system which connects the transmission of a car to its driven axle. In simpler words, drivetrain involves all the systems and equipment which take power and torque produced by the engine, from the transmission to the driven wheels.

Early cars were all rear-wheel-driven, but as time passed, R&D methods and technology improved, because of which, more drivetrain options emerged. In this feature article, we will be telling our readers the differences between Front-Wheel-Drive (FWD), Rear-Wheel-Drive (RWD), 4-Wheel-Drive (4WD) and All-Wheel-Drive (AWD).

Car Drivetrain Systems Explained

Rear-Wheel-Drive (RWD)
RWD on internal combustion engine-powered automobiles has been around since 1885 when Carl Benz developed the Benz Patent Motor Car, which of course is known to be the first car in the world.

RWD is a system in which, a driveshaft/propeller shaft takes the torque put out by the transmission and drives the rear wheels through a differential, which splits the drive between the two rear wheels. A RWD system requires the engine and gearbox to be longitudinally mounted so that the drive can be sent straight to the differential at the rear.

Car Drivetrain Systems Explained

A RWD car will have the slight disadvantage of having lesser space inside the car, as the driveshaft will have to go underneath the body, which is why some cars have the bump in their floor. But RWD cars have always pleased automotive enthusiasts, as according to them, they are more 'fun' to drive. Sliding the rear-end of the car out and having fun is something that began with RWD cars.
Car Drivetrain Systems Explained

Today, FWD cars outnumber RWD cars, but there are quite a few revered RWD cars in today's time and age as well. Most cars made by Mercedes-Benz are RWD, and most muscle cars even today are RWD, like the Ford Mustang, the Dodge Charger and Challenger, the Chevrolet Camaro, etc. In India, cars like the Mahindra Xylo, Maruti Suzuki Omni, Toyota Innova, etc. are RWD.

Front-Wheel-Drive (FWD)
Experiments with FWD cars began as early as 1895, and the experimenting went on over the next few decades. The first production vehicle to use FWD was the BSA three-wheeler in 1929, yet the experimenting continued, with many manufacturers taking an interest in FWD.

Car Drivetrain Systems Explained

It took decades to develop FWD because of the complexity it involves. The front wheels have to both drive and steer the car, which is exactly what makes it complex. Though many engine configurations were tried, it was found that the engine had to be mounted transversely to get the gearbox and differential to fit in the same space.

The decades spent on developing FWD seems worth it when looked at from the 21st-century perspective. Most of the cars on the roads today are FWD. All the hatchbacks, and almost all sedans today are driven by their front wheels.

Car Drivetrain Systems Explained

FWD is more efficient than RWD, and it also saves some space inside the car as it does not require a driveshaft under the body. However, most FWD cars have understeer as its natural character in which the front end of the car goes out when a corner is taken too fast.

Four-Wheel-Drive (4WD):
4WD vehicles are those vehicles with drive going to both the axles, in turn, transferring torque to four wheel ends. It is optimized for off-road driving conditions. 4WD vehicles are typically equipped with a transfer case which allows a vehicle to switch between RWD and 4WD operating modes, either manually or automatically.

Car Drivetrain Systems Explained

The roots of 4WD systems can be traced back to 1893 when English engineer Bramah Joseph Diplock patented a Four-Wheel-Drive system and built a vehicle that displayed an ability to travel on challenging terrain. Well, the purpose of 4WD systems have stuck to the same roots ever since, as they are until this day, used to travel on tough terrain, sometimes for a purpose, and sometimes for pleasure.

4WD vehicles are also termed as Four-by-four (4×4) vehicles. It is so because the first figure in 4x4 represents the total number of wheels and the second represents the number which is powered. Alternatively, a 6×4 vehicle has six wheels, out of which only four are driven.

Car Drivetrain Systems Explained

Today, a 4WD system can be found on most Big SUVs and pickup trucks across the world. In India, vehicles like the Mahindra Scorpio Getaway, Mahindra Thar, Toyota Fortuner, Mitsubishi Pajero, Maruti Suzuki Gypsy, etc. are examples of 4WD vehicles.

All-Wheel-Drive (AWD):
All-Wheel-Drive uses the same basic principles as 4WD, but uses either FWD or RWD as its primary drive in most situations, sending power to the other axle only if required. The difference between AWD and 4WD is basically in its application. While 4WD is designed to take the vehicle off the road, AWD is designed to keep the vehicle on the road. Quite literally.

Car Drivetrain Systems Explained

The application of AWD today is mostly in powerful cars, and in some soft-roaders as well if required to traverse on some rough terrain. On powerful cars, an AWD helps put the power down to the road better, and it handles better which in turn makes it faster and quicker. AWD systems can detect which wheel needs the most power at the particular moment and which wheel needs none at all. On soft-roaders, it can get the car out of a sticky situation.

AWD systems first came about a few years after the first 4WD system was developed, when in 1903 Dutch brothers Jacobus and Henrik-Jan Spyker revealed an AWD hill-climb racer named Spyker 60 H.P 4WD. Though it was at the time called 4WD, it was essentially an AWD system.

Car Drivetrain Systems Explained

AWD systems changed the world of motorsport when Audi introduced the Audi Quattro Rally car. Since then, the world of rallying has never gone back to the RWD configuration. Today, AWD systems are used on a variety of vehicles. From the likes of the Lamborghini Aventador and Porsche 911, to the Bentley Continental GT and Audi A8, and also on some soft-roaders like the Mahindra XUV 500, and Renault Duster.

AWD systems and 4WD systems are sometimes offered as optional extras, giving the customers a choice.

Other Drivetrain systems:

Individual Wheel Drive (IWD):
IWD is the drivetrain used in most electric cars, which are gaining more popularity as we are heading towards an electric car-driven world. It works exactly as the name suggests since it is driven by electric motors which are placed at each wheel end, driving that wheel alone. IWD has many advantages and almost no disadvantages.

Car Drivetrain Systems Explained

Being placed at the axle ends, all it requires is the power cables to reach the electric motors. Individual-wheel-drive also allows flexibility in the way power is sent to the wheels, and the car's management systems can detect and send power only to those wheels which have the maximum traction without the involvement of any complex mechanical bits.

H-Drive:
A H-Drive drivetrain layout is not very well known, as it has seen only military use, and even among military vehicles, it is a rare drivetrain system. It features individual wheel stations instead of axles. The gearbox is connected directly to a single differential which splits the drive into separate left and right drives.

The left and right drives are further split by another set of differentials to the front and rear wheels. At each wheel station, there is a bevel box which drives the half-shaft out to the wheel. This system is used on some heavy off-road vehicles which use 6x6 or 8x8 configurations.

Car Drivetrain Systems Explained

This system allows every wheel station to have individual suspension, in turn giving the tyres more traction. There is increased ground clearance as well because there is no axle and differential or even the central driveshaft.

DriveSpark Thinks!
Going by the current happenings in the Automotive Industry, it does seem like Individual Wheel Drive is the way forward. It is very obvious that electric cars are the future, and having motors on the four wheels of a car will make things very flexible for the driver, irrespective of the type of vehicle.

Car Drivetrain Systems Explained

Depending on the terrain, load and also the type of vehicle, the computers aboard the cars can decide to send power to individual wheels, making the vehicle a FWD or RWD or AWD, maybe even 4WD, as and when required, all within a few moments.
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Read more on: #off beat
Article Published On: Wednesday, June 21, 2017, 21:10 [IST]
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