How does four-wheel drive work

What is all-wheel drive?

All wheel drive (AWD) vehicles send power to all four wheels. This can be done in a number of ways, but the ultimate goal is to improve the vehicle's traction and performance. Although four-wheel drive is a more expensive option and uses more parts (more things that can break), it has some huge advantages. This includes:

• Best Acceleration: When all four wheels reduce power (usually), it is easier to pick up speed.

• More stable acceleration: When the power is distributed between the two axles, there is less wheel spin and hence the acceleration becomes more stable.

• Better grip on slippery roads: Whether it's snow on the ground or heavy rain, XNUMXWD will make the wheels more grippy when accelerating or maintaining speed. All-wheel drive also reduces the chance of the car getting stuck in mud or snow.

There is a slight difference between XNUMXWD and XNUMXWD. In the US, for a vehicle to be labeled "all-wheel drive", both axles must be able to receive power at the same time and rotate at different speeds. If the vehicle has a transfer case, which means that if both axles get power, then they will be forced to spin at the same speed, then it is four wheel drive, not four wheel drive.

Many modern SUVs and crossovers use all-wheel drive systems labeled "Four-Wheel Drive". This allows the axles to rotate at different speeds and has many practical uses, meaning that manufacturers often reserve true four-wheel drive for heavy-duty and off-road vehicles. They can be labeled as all-wheel drive because they technically allow all four wheels to drive the car forward. Labeling the XNUMXWD drivetrain as XNUMXWD also makes it more rugged and more like a dedicated SUV.

How does four-wheel drive work?

If the car has a center differential, then the transmission layout resembles a rear-wheel drive installation. The engine runs in the gearbox and then back into the differential. Usually the engine is installed longitudinally. Instead of being connected to the rear differential, as in a rear-wheel drive car, the driveshaft is connected to the center differential.

The center differential works in the same way as differentials on any of the axles. When one side of the differential spins at a different speed than the other, it allows one side to slip while the other side gets more power. From the center differential, one driveshaft goes straight to the rear differential and the other goes to the front differential. Subaru uses a system that is a variation of this type of all-wheel drive. Instead of the driveshaft going to the front axle, the front differential is built into the transfer case along with the center differential.

If the car does not have a center differential, then its location is likely to resemble a front-wheel drive vehicle. The engine is probably mounted transversely, transmitting power to the gearbox. Instead of directing all of the power to the set of wheels under the engine, some of the power is also sent to the differential on the opposite axle via a driveshaft extending from the gearbox. This works similar to the center differential scheme, except that the transmission almost always gets more power than the opposite axle. This allows the car to use all-wheel drive only when more traction is needed. This type of system provides improved fuel economy and is generally lighter. The disadvantage is the lesser performance of all-wheel drive on dry roads.

Various types of all-wheel drive

There are two main types of all-wheel drive used in cars today:

• Permanent four-wheel drive: This type of transmission uses three differentials to efficiently distribute power to all four wheels. In this arrangement, all wheels receive power all the time. Very popular all-wheel drive systems with this arrangement include the Audi Quattro all-wheel drive and Subaru's symmetrical all-wheel drive. Rally racing cars and their road-going equivalents use this type of AWD setup almost universally.

• Automatic four-wheel drive: There is no center differential in this type of all-wheel drive. A gearbox driving one set of wheels sends most of the power directly to the front or rear axle, while a driveshaft sends the power to a differential on the opposite axle. With this type of system, the driver only gets the benefits of all-wheel drive in low traction conditions. This setup takes up less space than the alternative and allows the vehicle to perform more efficiently when operating as front or rear wheel drive.

Where is the best place to use all-wheel drive?

• Vehicles that see a lot of weather: It's easy to see why people living in very snowy or rainy areas prefer XNUMXxXNUMX vehicles. They are less likely to get stuck and more likely to disengage if they get stuck. Combined with weather-appropriate tires, all-wheel drive is almost unstoppable.

• Productivity Apps: Grip is important for powerful vehicles. Strong traction allows the car to decelerate faster and accelerate faster out of corners. All Lamborghini and Bugatti use four-wheel drive. While there is an increased risk of understeer (the front wheels lose traction in a corner), modern technology makes this largely a non-issue.

What are the disadvantages of all-wheel drive?

• Sending power to both axles makes the car less fuel efficient. It has to use more power to get all the wheels spinning and more to make the car accelerate.

• Handling characteristics are not to everyone's liking. While all-wheel drive allows consumers to experience some of the best benefits of both front-wheel drive and rear-wheel drive vehicles, it can also exhibit the negative characteristics of both. Some vehicles may understeer when the front wheels receive too much power in corners, while others may oversteer when the rear wheels receive too much power. This is really a matter of taste of the driver and the particular car.

• More parts means more weight. Because of the weight, the car performs worse and consumes more fuel. More parts also means more things that can break. On top of the fact that XNUMXWD vehicles usually cost more, maintenance and repairs can also cost more in the future.

Is all wheel drive right for me?

For people living in areas that get a lot of snow every year, XNUMXxXNUMX vehicles make sense for everyday use. The higher cost and worse fuel economy are well worth driving down the road in heavy snow or driving through a snowdrift accidentally left behind by a tiller. In such regions, all-wheel drive vehicles also have a high resale value.

However, many traction problems can be solved with seasonal tires. Most roads can be driven frequently enough in most places that four-wheel drive is rarely needed. All-wheel drive does not improve braking or steering performance on slippery roads, so cars using it are not necessarily safer.