Typically, cars in come in three specific types: front wheel drive, rear wheel drive and 4 wheel drive. While many drivers have their own preference - such as finding a type that suits their driving style and needs - many also aren’t aware of the key differences, advantages and disadvantages of each.
The drive train on vehicles follows one of three configurations; front wheel drive, rear wheel drive, and four wheel drive. Of course, there are switchable systems which can transform a two wheel drive car into a four wheel drive one as necessary, but the basic configurations still exist. All of these have their own advantages and disadvantages, but which – if any - is best? Here, we look at what makes these configurations different, and in which situations one may prove superior to the others.
Front, rear and 4 wheel drive cars all have different advantages and disadvantages.
In short, the drive wheels are the ones that actually supply power from the engine to the road, moving the car. With two wheel drive vehicles, this becomes a simple choice between being pushed along or being pulled along – the fundamental difference between front wheel drive and rear wheel drive.
Two Wheel Drive – Pull or Push?
Rear Wheel Drive
To be pushed along by the rear wheels was, for a long time, the configuration of choice, because it was simple to manufacture. With this system, the engine produces the power which is then delivered to the rear wheels via a drive shaft that connects the two areas. The drive shaft power has to be transferred through 90 degrees at the rear wheels and this requires the use of a differential gearbox, which can be seen as a large, lumpy affair in the centre of the rear axle.
The front wheels are used only for steering and this effectively splits up the work any one set of wheels are doing. Almost all trucks are rear wheel drive and it is common to see the central drive shaft spinning on these, if you look between the wheels.
Advantages and Disadvantages
They may be simple, but rear wheel drive systems are also, generally, heavier, having a drive shaft, axle-mounted differential gearbox and a complex axle and rear suspension system. They also suffer from an increase likelihood of wheel spin and possible loss of control of the back end with more powerful cars, but tend to perform better under braking as the weight distribution is more balanced. Race cars tend to be rear-wheel drive, with around 65% of the weight towards the rear to help prevent wheel spins and traction problems.
Rear Wheel Drive Cars
While rear wheel drive was the normal configuration for all cars, it has remained the standard on cars typically considered to be performance vehicles. All BMW’s – apart from the four wheel drive versions – many larger Mercedes Benz, Jaguar models, Aston Martin, Porsche, and performance Nissan’s and Toyota’s are all rear wheel drive, along with every American muscle car. It’s hard to imagine a Dodge Charger, or a Ford Shelby 500 taking off from the line with the front wheels spinning and pouring out smoke!!
Many performance vehicles, such as BMW cars, use rear wheel drive systems
You Spin Me Right Round
Rear wheel drive cars have a reputation for being a bit of a handful to drive in even slightly tricky conditions. Wet roads can be tricky, while ice or snow-covered roads can spell a nasty rear end slide if power is applied too quickly – remember, rear wheel drive cars tend to have larger engines and are the most powerful in a manufacturer’s range. Many manufacturers have countered this tendency for the rear end to kick out under acceleration by adding limited-slip differential gearboxes on the rear axle.
The limited slip differential gear arrangement is a system that allows for some difference in angular velocity of the output shafts, but imposes a mechanical limit on the disparity. This means that any slides and wheel spins by the rear wheels can be absorbed by the differential gearbox, leading to a reduction in power being delivered to the wheels, stopping the potentially uncontrollable skid taking place as it starts to happen.
Taking Back the Traction
Furthermore, many manufactures include a traction control system on their cars to achieve the same result. Traction control – such as the BMW ACS system – is usually a software-controlled system which recognises when a wheel loses traction with the road, and automatically limits the power being supplied to it to allow traction to be regained.
Traction control is also advantageous as it can recognise loss of traction on fast cornering as well, and will fight to overcome a vehicle in danger of losing grip, making it harder for the car to slide and potentially making cornering faster in a car fitted with the system.
Traction control is also advantageous as it can recognise loss of traction on fast cornering as well, and will fight to overcome a vehicle in danger of losing grip, making it harder for the car to slide and potentially making cornering faster in a car fitted with the system.
Front Wheel Drive
This is the system, found on many low end options and family cars, which involves the front wheels both supplying the engine power to the road and carrying out the steering. Front wheel drive tends to be fitted to cars with either smaller engines, or with bigger engine bays. The main reason for this is that the engine is usually seated crossway in the engine bay, parallel to the front axles – with (usually) four pistons running in a line between the wheels, rather than from front to back as with a rear-wheel drive car – and is referred to as a Transverse engine.
Many front wheel drive vehicles typically feature a transverse engine.
Typically, the transverse engine has a smaller gearbox which is housed within the same casings as the engine itself, making one complete unit rather than the two discrete units that bolt together to make the rear-wheel drive unit. Short, stubby, drive shafts coming from the gearbox connect directly to the front wheels, applying power to them.
It’s All Up the Front
This configuration means that the vehicle is missing the extra weight of a drive shaft, running from the engine to the rear axle, as well as the fairly large and heavy differential gearbox. It also tends to make the engine and gearbox unit smaller, further saving weight and ultimately leading to smaller, more economical cars.
A front wheel drive vehicle typically places around 60% of the entire weight over the front wheels which can lead to stability problems under acceleration and braking, so it is a system that tends to be applied to small to medium sized family cars, rather than performance cars, for which rear wheel drive is preferable. Front wheel drive cars can also be fitted with traction control (on the front wheels only) which can help with some safety aspects but, generally, this isn’t as effective as those systems found on rear wheel or four-wheel drive cars, as the rear end isn’t stabilised and can break out if treated incorrectly.
Front Wheel Drive Cars
Obviously, front wheel drive cars lack complexity when it comes to the rear end configuration and rear suspension system. Typically, the rear axles will be stub units – as opposed to one axle that extends right across the car – with independent suspension units attached to each wheel. This means that each wheel acts independently and this leads to a less bumpy ride. Consequently, this makes the whole chassis and structural parts of the car very simple and, therefore, they are cheap and easy to manufacture. This helps to further drive costs out of the vehicle and ensures that small cars remain cheap to buy. Small Peugeots, Renaults, Fords, many Japanese models, and even vehicles like the Audi A3 are front wheel drive.
Four Wheel Drive
Off-Road
Vehicle stability is dependent upon the state of the ground beneath the wheels; smooth, tarmacked roads are fine for any vehicle but, if it becomes a lot less stable, any two wheel drive vehicle will begin to suffer. If you add in lots of water or mud, then normal road vehicles will come to a halt. Only specialised four wheel drive vehicles, which are designed to go off road and have both the low end power and the traction to get out of almost anything the off-road tracks can throw at them, are suitable on less stable surfaces.
Many vehicles make use of 4 wheel drive to help with off-road driving
Typically, being a combination of both front and rear wheel drive vehicles, with all four wheels applying traction, it is very difficult to get stuck. Off-road four wheel drive vehicles, also referred to as all wheel drive cars, tend to be high torque, high power but lower speed vehicles, consisting of a cab section and an open top (but usually coverable) body behind, are also quite common, typically used as utility and work vehicles. These are usually seen on building sites and similar environments.
On-Road
Yet there are an increasing number of four wheel drive systems finding their way into dedicated road vehicles, with many top end manufacturers fielding at least one four wheel drive road car amongst their available models. The main reason for doing this – since cost is rarely an issue to someone buying a vehicle of this pedigree – is the increased stability under what is usually a much higher power delivery than with smaller, family cars. Many of these vehicles may develop several hundred horsepower and getting that safely and effectively delivered to the road surface requires it to be distributed across all the wheels. This prevents wheel spins and the possibility of one set of wheels breaking away from the surface and creating a dangerous situation.
Four Wheel Drive For The Masses
Much engineering work has gone into creating very small and effective engine and differential gearboxes to keep weight down and drive efficiency up. Vehicles of this class have been developed with either switchable two to four wheel drive as well as “always on” four wheel drive so it can be selected as required. Road-going four wheel drive cars became viable when Audi introduced their grapefruit-sized differential gearbox, as first fitted to the evocative Quattro model, with in-house designed variations of this small but highly effective piece of engineering finding its way onto many other vehicles following Audi’s lead.
On-road four wheel drive cars are usually amongst the flagships of a company and are epitomized by the Audi Allroad and RS6, the Volvo XC70 (beloved of Jeremy Clarkson), and the Mercedes Benz 4Matic range.
Sports Utility Vehicles
As four wheel drive vehicles have become more popular, 4x4 crossover vehicles have risen in favour. Sports Utility Vehicles (SUV’s) are seen as either a high quality work vehicle or a road vehicle that is capable of going off road as necessary. SUV’s have superior ground clearance and are fitted with car tyres that allow the vehicle good grip in tricky or unstable ground conditions.
SUVs and crossover vehicles commonly are also 4 wheel drive cars
Almost all high end car manufacturers now produce an SUV, with examples being the BMW X-series, the Audi Q series, and the Land Rover Discovery range. SUV’s are now available from every Japanese manufacturer, with those worldwide who don’t yet have one in their range struggling to catch up in this expanding market. One downside to these behemoths is that, in order to make these relatively high up vehicles stable in cornering and at speed, the manufacturers have had to beef up the suspension systems, which can lead to a fairly firm ride. Because of their large and lumbering nature, SUV’s are also known as Chelsea Tractors!
So What’s Best For You?
The best type of drive, rather unsurprisingly, depends upon the use that you are going to put the vehicle too. If you want something small, light and fuel efficient around town, you would probably go for a front wheel drive car. If you want a medium range car with more performance, then a rear wheel drive car would suit you better. If you desire a hyper-performance road car, then four wheel drive would be the best choice and, if you are even thinking about hitting the fields and grassy knolls, you wouldn’t consider anything other than a dedicated off-road four wheel drive vehicle.
There is no correct answer regarding which type of drive is best, as there are simply different situations where one type will have advantages over the others and perform accordingly. Much of what’s right for you depends upon your driving style and tastes.
What Kind of Driver Are You?
If you are a sedate driver “around town” then you would be best off with a small front wheel drive car which is ideal for coping with traffic and returns a good level of miles per fuel gallon. If you are more prone to longer - and possibly faster – distances, then you would do better with a rear wheel or four wheel drive car for added comfort and stability. If you plan on taking your pride and joy through muddy puddles in a carefree and bump-free fashion, then any of today’s SUV’s would be right up your street, and for carting equipment or supplies around, you really do need a four wheel drive utility vehicle.