Front-Wheel Drive

Front-wheel drive, abbreviated FWD, is the drivetrain layout in which the engine sends its power to the front wheels, the same wheels that steer the car. It is by far the most common configuration for everyday passenger cars, and it exists because it offers a compact, economical and space-efficient way to package a vehicle. By concentrating the engine, gearbox and final drive at one end and dispensing with the need to run power to the rear, it allows smaller, lighter and cheaper cars to be built.

The heart of a front-wheel-drive car is the transaxle, a single unit that combines the gearbox and the differential alongside the engine, usually mounted transversely across the engine bay. From the differential, a pair of half-shafts runs out to each front wheel, each fitted with constant-velocity joints. These joints are essential to the layout, because the front wheels must both steer and drive at the same time; the constant-velocity joint transmits drive smoothly through the varying angles created as the wheels turn and the suspension moves, something a simple universal joint could not do without vibration.

The packaging advantages of this arrangement are considerable. With no propeller shaft running the length of the car and no rear differential, the floor can be flatter, the cabin roomier and the boot deeper, and the whole drivetrain can be assembled as one module and dropped into the body. The layout also delivers good traction in normal conditions, because the weight of the engine sits directly over the driven wheels, pressing them into the road; this is particularly helpful when pulling away on wet or snowy surfaces, and it is a large part of why front-wheel drive became the default for mainstream cars.

The layout is not without its compromises, and these emerge most clearly when power and grip are pushed. Because the front tyres must share the tasks of steering, braking and putting down power, a front-wheel-drive car tends towards understeer, running wide at the front when cornering hard, as the front tyres reach the limit of their grip first. Under strong acceleration it can also suffer torque steer, a tugging at the steering wheel caused by unequal drive being fed through half-shafts of different lengths, and traction can be overwhelmed more easily in a powerful car than it would be at a driven rear axle.

For these reasons front-wheel drive is usually contrasted with rear-wheel drive, which separates the jobs of steering and driving between the two axles for sharper handling at the expense of packaging and cost, and with all-wheel drive, which adds traction by driving both ends. As one of the forms of two-wheel drive, front-wheel drive remains the pragmatic choice for the great majority of cars, its modest dynamic shortcomings outweighed for ordinary use by its efficiency, interior space and dependable wet-weather traction.