What is the difference between: RWD, FWD, AWD or 4WD?
What is the drivetrain and what does it do?
A car’s drivetrain is a system that links the engine to the wheels, enabling the vehicle to move and the driver to change gear. The drivetrain sends power from the engine to the drive wheels, which – depending on the type of drivetrain the car has – are the front wheels, rear wheels or all four wheels in the case of four-wheel drive.
A drivetrain consists of various components, including:
- Drive shaft
- Constant-velocity joint
- U-joint
- Differential
- Half-shafts
The drive shaft supplies torque from the engine to the drive wheels, and it is only absent on front-wheel-drive cars. The constant-velocity joint is generally only present on front-wheel-drive cars, linking the front axle to the front wheels. It is a joint that moves at a constant velocity and it enables the axle to move while the drive wheels are turning.
The U-joint is a flexible element of the drive shaft, which enables the rotation of the shaft in the event of potholes or bumps. The differential is an indispensable component for sending the power to the drive wheels. The half-shafts are at the sides of the differential, helping to distribute the power to the drive wheels.
Rear-wheel drive (RWD): pros and cons
In rear-wheel-drive cars, all the engine power is distributed to the rear wheels. This solution allows for the engine to be positioned at the front or back. In general, RWD is used on high-end cars, particularly sports cars with a lot of power.
Rear-wheel-drive cars have significant advantages:
- Better Sports handling thanks to the better weight balance of the car
- Better control of the vehicle for an experienced driver
- Faster and immediate acceleration with a minimal delay
- Highly efficient, fluid braking, with a lower risk of skidding
Obviously, there are also some disadvantages of rear-wheel-drive cars:
- Rear-wheel-drive cars are generally high-end cars that cost more
- The rear-wheel drivetrain takes up more space in the vehicle cabin than front-wheel
- Higher fuel consumption because more power is required to move the drive wheels
- Rear-wheel-drive cars are harder to drive in snow and ice
Four-wheel drive (4WD or 4x4): pros and cons
In four-wheel-drive cars, the engine power is distributed to all four wheels, so to both axles rather than just one like on front- and rear-wheel-drive cars. 4WD or 4x4 cars do not have the centre differential; they have a transfer case for gear reduction.
This configuration means that you don’t always have to use the four-wheel drive, only when necessary. In normal driving conditions on tarmac, cars use the front-wheel drive (occasionally rear-wheel drive) because the absence of the centre differential allows the front and rear axles to turn at the same speed. When conditions require, the rear-wheel drive kicks in and low-range gears can be used to handle complex situations.
The advantages of 4WD are:
- More traction in dangerous driving situations, like ice, snow and mud
- The possibility of using low-range gears to get out of difficult situations, like a very steep section or a lot of mud
- Better grip on tarmac thanks to the heavier weight of the 4x4 drivetrain
- Safer when driving off-road
In terms of the disadvantages of 4x4 cars, it is important to consider:
- Higher cost to buy the vehicle
- Higher maintenance costs because of additional components in the drivetrain system
- Higher fuel consumption compared to RWD or FWD cars
- Greater stopping distance because of the extra weight of the drivetrain system
All-wheel drive (AWD): pros and cons
None of the drivetrain systems are best; you should assess each type based on your personal needs and the road conditions you will face. Plus, in order to take full advantage of the drivetrain you choose, it always needs to be combined with the right high-quality tyres that should be well maintained.
Front-wheel-drive cars are more efficient in terms of costs, they consume less fuel and the understeer is easier to control for an inexperienced driver. On the other hand, the weight on the front axle reduces handling and the car’s responsiveness.
Rear-wheel-drive cars offer a better drive, a high level of grip on bends and greater steering control, with excellent traction on acceleration. However, RWD makes the car harder to control if you spin due to oversteer, it is more expensive to buy and maintain, and the friction increases fuel consumption.
AWD and 4WD cars offer better control in difficult road conditions, excellent grip on acceleration and a higher level of safety. However, they are more expensive, heavier and consume more fuel, with lower driving efficiency in all conditions.
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