The wheels driven by a car’s engine or its electric motor have a significant effect on it. They dictate what the car is like to drive, how much interior space there is, how it behaves during cornering, how much grip it has in a given situation and even its fuel-efficient it is.
Put simply, there are three different layouts of driven wheels on most cars: front-wheel drive, rear-wheel drive and four-wheel drive (four-wheel-drive cars can also be split into separate sub-categories, but we’ll go into more depth on that later).
Front-wheel-drive models tend to have more space inside, because they don't have drivetrain components running the length of the car to power the rear wheels. Everything sits under the bonnet, which frees up more cabin space.
Rear-wheel-drive cars often have a sharper and more direct feel to the steering, because the front wheels only have to steer the car, but they lose a little interior space to the driveline components that run from the engine and gearbox to the rear wheels.
Finally, four-wheel drive offers the advantage of much better traction, because all four wheels can move the car forwards, which means it’s more likely to find grip in slippery conditions. Four-wheel drive is almost always better for off-roading, and its extra grip can make it an asset for performance cars, too.
Four-wheel-drive systems are similar to, but not quite the same as, all-wheel-drive systems: broadly speaking, while four-wheel drive powers all four wheels of a car continuously, all-wheel-drive vehicles can send power to all four wheels, but not necessarily all the time.
The downside of four-wheel drive and all-wheel drive is that the extra mechanical components required to send the engine’s power to all four wheels make four-wheel-drive models comparatively heavier than two-wheel drive equivalents, so four-wheel-drive cars tend to be less fuel-efficient. The extra friction of the additional driveline components also increases fuel consumption.
Electric cars sidestep some of the issues for all layouts, because they can have motors located at the front or the back (or both), and the lack of a gearbox in most EVs also helps with the overall packaging.
Read on for a more in-depth look at each of the drivetrain layouts.
Front-wheel Drive (FWD)
The main advantage of a front-wheel-drive layout is packaging. There’s no need to send power to the rear wheels via a long driveshaft, the vehicle’s drivetrain is much more compact and it doesn’t intrude as much on cabin space. A classic example of this is the original 1959 Mini, one of the first popular mass-produced front-drive cars. Thanks to its then-revolutionary drivetrain layout, it could comfortably carry four passengers and luggage, despite its tiny proportions. FWD cars also often have a fuel economy advantage, particularly over four-wheel-drive cars.
Front-wheel-drive cars also tend to have their engine and gearbox installed transversely (i.e. east-west in the engine bay) rather than longitudinally (north-south) as is normally the case with rear-wheel-drive cars. This makes the drivetrain even more compact, and frees up yet more interior space.
There are downsides to a font-wheel-drive layout, though. Putting too much power through those front wheels gives rise to a phenomenon known as ‘torque steer’. This is when torque from the engine influences the steering of a car, and the driver experiences this as a ‘tugging’ of the wheel, with the car wanting to effectively steer itself away from your chosen course.
This happens when the engine's torque – or pulling power – overwhelms the front wheels. In front-wheel-drive cars with transverse engines, the way the engine and gearbox are arranged means that the drive shafts (which transfer power from the gearbox to the driven wheels) are of unequal length. This can cause the car to veer when the torque kicks in under hard acceleration.
Front-wheel-drive cars also have a tendency to understeer. This is when the front of the car loses grip and wants to push onwards, causing it to run wide of the driver's intended steering line.
Another downside of front-wheel-drive cars is traction – under acceleration the weight of the engine in the car shifts rearwards, effectively making the font of the car lighter and making it more likely that the front wheels will spin – although the effects of this can be mitigated by traction control.
That’s not to say front-wheel-drive cars can’t be fun. Even though torque steer only tends to affect more powerful cars, many hot hatchbacks are front-wheel drive, including the Honda Civic Type R, the Ford Focus ST and the Volkswagen Golf GTI.
Front-wheel drive is most common in models and bodystyles where space is at a premium and a lot of emphasis is placed on efficient packaging. For instance, small cars such as the Renault Clio and the Volkswagen Polo are front-wheel drive, as are most family hatchbacks, such as the Ford Focus or (the majority of) Volkswagen Golfs. Increasingly, front-wheel drive is used instead of four-wheel drive in many road-biased SUVs and crossovers, especially smaller ones, such as the Ford Puma or larger family crossovers, such as the Nissan Qashqai or the Peugeot 3008.
Rear-wheel-Drive (RWD)
Rear-wheel drive is traditionally the layout of choice for sports cars, executive cars and luxury cars. This is because it can deploy more power to the road than a front-wheel-drive car without the risk of torque steer, because the driven wheels aren’t the ones doing the steering. That makes it ideal for sports cars, where handling is a priority and interior space is less important, and for luxury cars, which favour smoothness.
In handling terms, rear-wheel-drive vehicles are more likely to oversteer. This is where the rear wheels lose traction under acceleration and the back of the car wants to 'overtake' the front, causing it to spin.
Rear-wheel drive vehicles can hamper a car's interior space. The driveshaft needs to run the length of the car, which results in what's known as a transmission tunnel. That creates a hump along the centre of the floor of RWD cars, which is most obvious in the rear footwell. The engine and the gearbox are normally installed longitudinally (i.e. front to back in the engine bay), which means they take up more of the overall length of the car, necessitating a longer bonnet or a certain amount of intrusion into the cabin – or both.
Not every car with a RWD vehicle layout has these issues, though. Mid-engined RWD sports cars – such as the Lotus Elise, the Porsche Boxster or the Alpine A110 – have their engines mounted behind the rear seats in a transverse (horizontal) layout.
Some cars, such as the Porsche 911, have an engine behind (or over) the rear axle, driving the rear wheels. Some electric models also feature a rear-drive, rear-motor layout, and seeing as electric motors tend to be physically far smaller than equivalent internal combustion engines, they don’t tend to eat into boot space. Examples of rear-drive, rear-engine EVs include the Honda e city car, the BMW i3, and the single-motor version of the Tesla Model 3.
More traditional examples of rear-wheel-drive models include compact executive saloons such as the BMW 3 Series (which are also available with four-wheel drive), sports cars such as the Mazda MX-5, and larger luxury cars such as the BMW 5 Series or the Jaguar XF.
Four-wheel Drive (4WD)
Four-wheel drive is the most robust type of the two systems that can drive all four wheels of a car. It’s also the more traditional type, and you’ll find 4WD systems in rugged, old-school off-roaders, 4x4s, SUVs and pick-up trucks – ones that the manufacturers expect to undertake some serious off-road challenges.
4WD vehicles, such as the Land Rover Defender, the Toyota Hilux, the Jeep Wrangler or the Suzuki Jimny, tend to use mechanical connections, with front, centre and rear differentials and transfer cases to send power to all four wheels. In most modern 4x4s, these can be engaged and disengaged via electronically operated buttons or knobs.
These types of 4x4 also tend to have high-range and low-range modes, which can be selected via a switch or sometimes with a physical lever that looks a bit like a second gearstick. Low gear is essentially a crawler mode, which is ideal for heavy-duty off-road work, while high range is designed for lighter duties and higher-speed on-road driving.
Four-wheel drive can be a permanent, continuous system, where drive is always sent to all four wheels, or it can be part-time four-wheel drive, where the driver can choose between two-wheel drive and four-wheel drive. Two-wheel-drive modes generally help to save fuel and they tend to drive the rear wheels, with drive to the front axle disconnected.
All-wheel Drive (AWD)
If your car has all-wheel drive as opposed to four-wheel drive, it probably sends power to the wheels via viscous couplings or multi-plate clutches instead of a permanent mechanical connection. These sorts of systems apportion the drive automatically to wherever it’s needed, with no input from the driver of the car.
Many AWD vehicles allow you to select specific drive modes to control where the power goes, but this is generally a lesser degree of control than you'd find with a selectable four-wheel-drive system.
AWD systems come in either permanent or part-time forms. As the name implies, permanent AWD drives all four wheels continuously, while part-time all-wheel drive will be two-wheel drive in normal conditions (generally the front wheels in an SUV or a crossover) and deliver better fuel economy.
Plug-in hybrids can complicate matters. They are often effectively two-wheel drive as far as the petrol or diesel engine is concerned, with the electric motor providing the four-wheel drive element.
Examples of AWD cars include many family SUVs such as the Mazda CX-5 or the Skoda Kodiaq (though these are also available with front-wheel drive), or four-wheel-drive performance cars such as the Audi S3 Sportback, the Volkswagen Golf R, and the BMW M135i.