Four-wheel drive cars explained

More grip and less chance of getting stuck in snow: all you need to know about four-wheel drive cars and all-wheel drive cars

BuyaCar team
Dec 13, 2019

Most cars use their engine to power two wheels, either at the front of the car or the back. There are advantages to both approaches, but either should be fine for most drivers, most of the time.

But opting for a car with four-wheel drive, which sends the engine’s power to all four wheels, brings more capability. You'll have more grip when accelerating, for a start; you're less likely to get stuck on slippery surfaces; and these systems also help when towing.

Pros

More grip when accelerating
Less likely to get stuck in snow or off road
Better at towing

Cons

Usually heavier and less fuel efficient
 More expensive models
Makes little difference in corners

Do four-wheel drive cas have more grip?

Four-wheel drive helps improve a car’s traction, or grip, the benefits of which will be most apparent during acceleration or when off-roading. To move a car from standstill, you need plenty of power from the engine. Let's say your car produces 100hp, if it's a two-wheel drive car there will be 50hp being sent to each wheel. That power can very quickly overwhelm the two powered wheels and you'll begin to experience wheel spin.

 

In a four-wheel-drive car, the engine produces the same amount of power, but this is split between four wheels. So your 100hp car will be sending just 25hp to each wheel. Because there is less force, the tyres will have a much better chance of gripping and are less likely to spin.

This doesn’t make the car slower, because the total amount of power driving the car forward remains the same.

Four-wheel drive cars on snow, mud and ice

Once you’re on the move, four-wheel drive will also make you less likely to get stuck, as the engine’s power continues to be distributed between all four wheels.

If one, two or even three wheels start spinning on an extra slippery surface, then the remaining wheels that still have grip will help to keep the car rolling. In less than perfect conditions this can make a real difference to the performance of the car. 

However, a car’s grip on snow is generally more affected by the type of tyres you use. A two-wheel drive car with winter tyres is likely to have more grip than a four-wheel drive car on standard tyres. A four-wheel drive car with winter tyres is the ultimate choice. See more details in the video made by our sister publication, Auto Express, below.

Can four-wheel drive cars go faster in corners?

Four-wheel drive doesn’t give you more grip in corners, so doesn’t allow you turn into them at a faster speed.

That’s because your maximum cornering speed is affected by a sideways force - centrifugal force - which you can feel pushing you to one side when you turn quickly.

If you take a corner too fast, or if the road surface is slippery, then the centrifugal force can exceed the grip that the tyres have on the road, causing the car to skid or slide off the road.

However, four-wheel drive can make a car more stable and nimble in corners for two reasons

  • At the end of a corner, as it starts to straighten out, you can accelerate earlier for the same reasons that four-wheel drive is more likely to get you moving on a slippery surface: the power is distributed between all four wheels, so they are twisting with less force. This makes them less likely to lose grip and spin round.
  • Some cars have systems that send more power to one or two wheels when you accelerate in a corner. This is used to make the car feel sharper and more agile. This can be called yaw control or torque vectoring.

Four-wheel drive cars for towing

Weight and power are key to a good towcar. The heavier that you vehicle is, the more stable it’s likely to be when you hook a heft trailer or caravan to the back. And if you want to shift that weight, then a powerful engine is essential.

This means that you may find yourself having to rev the engine hard for maximum power to move away - particularly if you’ve stopped on an uphill slope.

Trying to send all that power through just two wheels can be too much for the tyres: you might find them squealing as they lose grip, or even spinning round on the spot.
By distributing that power between four tyres, a four-wheel drive car helps get a heavy car and trailer combination on the move.

Four-wheel drive cars off road

As well as improved grip on slippery surfaces, four-wheel drive cars also bring the benefit of being able to drive when only one wheel is touching the ground. This is especially useful when the ground is particularly rugged and the car can be left dangling in the air.

Four-wheel drive cars and fuel economy

The extra mechanical parts needed for a four-wheel drive car increases its weight, which means that you need a little more power - and fuel - when driving.

The system is also less efficient too, because you lose some energy for every wheel that you power - particularly through friction. Both factors mean that four-wheel drive cars have a lower mpg figure than an equivalent two-wheel drive model.

AWD or 4WD?

It used to be the case that a four-wheel drive (4WD) car was one that you would switch manually from two-wheel drive to four-wheel drive mode. An all-wheel drive (AWD) car was one that was constantly in four-wheel drive mode.

That’s no longer the case though. Manufacturers use both terms interchangeably, so you need to look a bit closer to work out which type of four-wheel drive car you’re looking at.

Types of four-wheel drive car

Selectable four-wheel drive This is the least sophisticated option available because it’s not designed to be used on the road and only works at slow speeds. You use a lever or dial to select four-wheel drive when you’re on a slippery or rough surface and need to remember to switch it off when you’re back on tarmac.

Permanent all-wheel drive / four-wheel drive This is the least efficient type of four-wheel drive because it’s constantly on

Intelligent all-wheel drive / four-wheel drive Also known as automatic four-wheel drive, this system continuously varies the amount of power going to each wheel to maximise fuel efficiency, grip and performance.

In normal driving, most of the power goes to the front or rear wheels, to improve fuel economy. If the car senses any wheel slipping, then it boosts power to the others. More sophisticated systems calculate the best power distribution for sharp and agile cornering.

This type of four-wheel drive is the most common. It’s used on supercars such as the Audi R8, big SUVs like the Range Rover Sport, and the little BMW 1 Series xDrive.
Some cars, such as the Renault Kadjar and Nissan X-Trail allow you to switch it off completely with a dial in the car.

How manufacturers label their four-wheel drive cars

Most of the time, a 4WD label will signify a four-wheel drive model. The AWD (all-wheel drive) badge is often stamped on models of this type too, but there are some manufacturers who have come up with their own ways of identifying a four-wheel drive car.

  • Audi Quattro
  • BMW xDrive
  • DS Hybrid4
  • Kia KX
  • Lexus E-Four
  • Mercedes 4Matic
  • Mini All4
  • Peugeot Hybrid4
  • Porsche 4
  • Seat 4Drive / X-Perience
  • Suzuki Allgrip
  • Volkswagen 4Motion

 

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