Front-wheel drive (FWD) is a form of engine and transmission layout used in motor vehicles where the engine drives only the front wheels. Most modern front-wheel drive vehicles feature a transverse engine, rather than the conventional longitudinal engine arrangement usually found in rear- and four-wheel drive vehicles.
Front-wheel drive (FWD) is a form of engine and transmission layout used in motor vehicles where the engine drives only the front wheels. Most modern front-wheel drive vehicles feature a transverse engine, rather than the conventional longitudinal engine arrangement usually found in rear- and four-wheel drive vehicles.Advantages of front-wheel drive
- Internal space: As the powertrain is a single unit contained within the vehicle's engine compartment, there is no need to dedicate internal space to a driveshaft tunnel or rear differential, increasing the volume available for passengers and cargo.
- Cost: Fewer components overall
- Weight: Fewer components mean less weight
- Fuel economy: Lighter weight means better gas mileage
- Greater drivetrain efficiency: The direct connection between the engine and transmission reduces the mass and mechanical inertia of the drivetrain compared to a rear-wheel drive vehicle with a similar engine and transmission, allowing for greater fuel economy.
- Assembly efficiency: The powertrain can often be assembled and installed as a unit, which allows for more efficient production.
- Slippery Surface Traction: Placing the mass of the powertrain over the drive wheels improves traction on wet, snowy or icy surfaces. Although the heavy load can be beneficial for traction in rear-wheel drive pickup trucks.
- Predictable handling characteristics: Front-wheel drive, front-heavy cars tend to understeer at the limit, which is commonly considered easier for ordinary drivers to correct than terminal oversteer, and less likely to result in a skid or spin.
- Better crosswind stability.
- Tactile feedback through the steering wheel informing the driver if a wheel is slipping.
- Front-wheel drive allows the use of left-foot braking as a steering technique.
Advantages of front-wheel drive
- The vehicle's center of gravity is typically further forward than a comparable rear-wheel drive layout. In front-wheel drive cars, the front axle typically supports about 2/3 of the car's weight (a far cry from the “ideal” 50/50 weight distribution). This is a contributing factor to the tendency of front-wheel drive cars to understeer.
- Torque steering can be a problem on front-wheel drive cars with higher torque engines (> 210 N·m) and transverse layout. This is the name given to the tendency of some front-wheel drive cars to pull left or right under hard acceleration. It is the result of displacement between the point around which the wheel rotates (which falls at a point in line with the points at which the wheel is connected to the steering mechanisms) and the centroid of its contact area. The traction force acts through the centroid of the contact area, and the displacement of the steering point means that a turning moment is generated about the steering axis. In an ideal situation, the left and right wheels would generate equal and opposite moments, canceling each other out, but in reality this is less likely to happen. Torque steering is often incorrectly attributed to different twist rates along the lengths of unequal front driveshafts. However, center point steering geometry can be incorporated into the design to avoid torque steering. This is how the powerful Citroen SM front-wheel drive car avoided the problem.
- The lack of weight shift will limit the acceleration of a front-wheel drive vehicle. In a rear-wheel drive car, the weight moves back during acceleration, giving more traction to the drive wheels. This is the main reason why almost all racing cars are rear-wheel drive. However, as front-wheel cars have the weight of the engine over the driving wheels, the problem only applies in extreme conditions.
- In some towing situations, front-wheel drive cars may have a traction disadvantage because there will be less weight on the drive wheels. Because of this, the weight the vehicle is rated to safely tow will likely be less than that of a rear-wheel drive or four-wheel drive vehicle of the same size and power.
- Due to geometry and packaging constraints, CV joints (constant velocity joints) attached to the wheel hub tend to wear out much sooner than their rear-wheel drive counterparts. The significantly shorter drive axles in a front-wheel-drive car cause the joint to flex through a much greater degree of movement, compounded by stress and additional steering angles, whereas the CV joints of a rear-wheel-drive car regularly experience angles and less wear than more than half of front-wheel drive vehicles.
- Driveshafts can limit how much the front wheels can turn, so they can increase the turning circle of a front-wheel drive car compared to a rear-wheel drive car with the same wheelbase.
- In low traction conditions (i.e.: ice or gravel), the front (drive) wheels lose traction first, making steering ineffective.
