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How Does AWD Work?

By Autolist Editorial | September 6, 2019

Many modern vehicles come equipped with all-wheel-drive. While AWD is most commonly available as an add-on feature for SUVs and crossovers, it may also be an optional upgrade for some modern flagship sedans. If you're considering spending the extra money for all-wheel drive, it's important that you understand what it is and how it works. That way, you can make an informed purchase. After all, you might not need AWD depending on your local climate and terrain.

Before examining the ins and outs of all-wheel-drive systems, it's essential to know that there's no one-size-fits-all AWD standard across all vehicles. Different manufacturers use different systems, and they may work in different ways. Here's an explainer that may help put all of the different names for all-wheel-drive and four-wheel-drive systems across different brands.

What Is AWD?

Vehicles equipped with an AWD system can deliver power to all four of the vehicle's wheels. Naturally, this helps vehicles to perform better and safer on off-road conditions, as well as on standard roads during inclement weather. An AWD vehicle offers better grip and faster, more consistent acceleration on slippery roads. In general, all-wheel-drive systems improve the security of driving the vehicle, helping it to feel more stable in some conditions. But unless you're using a torque-vectoring AWD system, you won't notice a performance boost in dry conditions.

How AWD Works: The Basics

There are different types of AWD systems, but most of them work the same way, in general. The big thing that an AWD system usually includes is a center differential, which is a set of gears that divides the transmission's power to the rear and front axles. An AWD system will usually also have wheel sensors that can tell if tires are losing speed or traction. If the sensors detect that a wheel (or wheels) is not performing correctly, it will say to the vehicle's computer to provide extra power as needed.

For example, say your car is stuck in a snowbank. You're trying to accelerate, but your back wheels are just spinning and spinning. Sensors will alert the car's computer of the problem, and the center differential would deliver extra power to the rear wheels, improving traction so you can free your vehicle.

Different Types of AWD

Not all automakers use the same specs, so one AWD car may offer better or worse performance than another. When it comes to car buying, it's up to you to learn about the drive mode included with that specific vehicle.

Here are the main types of AWD systems:

  • Symmetrical: With a symmetrical all-wheel-drive system, the front and rear axles are both constantly receiving power. If the vehicle loses traction, more power is delivered to the axle that requires it.

  • On-Demand: Some all-wheel-drive systems are based heavily on front-wheel-drive systems. With an on-demand AWD system, the front wheels receive all of the power, as long as you're driving in normal conditions. If the system detects slippage, it sends power to the rear wheels as well, helping to stabilize the vehicle. This system is often preferable because the car's handling feels more natural, and it also improves fuel economy.

  • Torque Vectoring: Like other AWD systems, torque vectoring systems can also deliver more power to the front or rear axle if necessary. The difference is that they can also provide more power to the back left or right wheels if needed. That gives you smoother handling, especially when taking corners. If you're hoping to improve your car's handling in dry conditions, you should seek out a vehicle with a torque vectoring system.

Is AWD the Same as 4WD?

While all-wheel-drive systems are very similar to four-wheel-drive systems, they're not exactly the same. Both systems do activate all four wheels simultaneously, and they're often advertised as the same thing, but differ on how they get to that point. To be classified as all-wheel-drive cars, both axles must be able to rotate simultaneously, but at different speeds.

On the other hand, four-wheel-drive vehicles have a transfer case, rather than a center differential, that forces both axles to spin at the same speed. The gears in the transfer case usually divide the power between the front and rear axles, so both axles deliver the maximum possible amount of torque.

Most 4WD transfer cases allow you to choose between low and high-range gearing. Low-range gearing lowers your maximum speed, but it also delivers more power for more extreme terrains. High-range gearing allows you to maintain your normal speed, so it's more suitable for icy, snowy, or rainy conditions.

The maximum torque and the ability to choose between low and high-range gearing are the significant reasons why 4WD systems appeal to those seeking more rugged vehicles for off-roading as well as commuting. AWD systems are usually automatically activated as required, so they're an excellent choice for those who prefer a set-it-and-forget-it approach.

Both systems have their benefits. AWD is typically preferred by those who mainly stick to standard roads, while 4WD is ideal for those who need something more rugged for low-traction, off-road terrain. Cornering is a significant factor to consider when choosing between the two. With 4WD systems, all wheels receive a fixed amount of power. That can make it challenging to take corners. With some AWD systems, on the other hand, power is delivered to the wheels that require it most. That means the vehicle can take turns more smoothly with better stability control.

Do You Need AWD?

As you can see, all-wheel-drive vehicles do offer some benefits, but should you pay a premium for them? There's no simple answer to that question — it depends on where you drive, how much the upgrade costs, and your personal preferences. If you're shopping for off-road vehicles, you may want to start by looking at four-wheel-drive vehicles. However, if you're looking to improve the safety of your daily commute, all-wheel-drive should do the trick.

The big reason why most people opt for AWD is that they live in areas that have slippery driving conditions. In other words, if you need AWD, you probably already know it. If you live somewhere that doesn't get a lot of snow, you'll probably be fine without all-wheel-drive.

That said, some people do prefer the overall feel of AWD. And for some, it's nice to know that the feature is there as a precaution. AWD also boosts the resale value of your vehicle, but it also increases the up-front price you pay.

You're already aware of the significant benefits associated with AWD, so let's take a look at the most significant drawbacks. A big one is fuel economy. Because your vehicle needs to use more power to get both axles spinning, it also uses more fuel.

All-wheel-drive vehicles also have more parts. That means the vehicle weighs more, which contributes to fuel use while also worsening handling. At the same time, some drivers do prefer that stable, consistent feel you get with a heavier car, not to mention the added stability due to the AWD system. It all comes down to preference. Besides the added weight, more parts also mean that there's more that can go wrong, and you may end up paying more than usual for repairs if you run into issues.

AWD Safety

Yes, AWD vehicles can be safer in rainy, snowy, or icy conditions, but they can also be more dangerous if you're not careful. One common mistake that AWD vehicle owners often make is relying too much on the system. It's essential that you realize that AWD doesn't affect braking. It's easy to feel comfortable driving on a dangerous road, not realizing that it can be difficult to brake. If you end up going too fast because you think an AWD system allows it, there could be a dangerous situation when it's time to take emergency action.

If you're considering an AWD vehicle because of your local weather conditions, you may find that upgrading your tires is a more affordable yet effective option. You may assume that you need AWD because your vehicle isn't performing well when all you need is a set of weather-appropriate tires. A quality set of winter tires actually will help with braking and steering, unlike AWD systems. So, while AWD drive systems can be beneficial, it's crucial that you don't use them as a crutch to drive irresponsibly.

Shop Smart

Only you can decide if you need a vehicle with an all-wheel-drive system. As a rule, it's probably not worth splurging for unless you know you're going to be driving on low-traction surfaces such as mud, dirt, snow, or ice. At the same time, you might be able to find a great deal on a car equipped with AWD, especially if you're buying used.

Spend some time researching each specific vehicle's AWD system. They're not all the same. If your goal is to improve stability on dry roads, a symmetrical or on-demand AWD system isn't going to help you, but a torque-vectoring AWD system might. Do your homework before you sign on the dotted line.

Finally, if possible, go out and test drive different vehicles. Try the same make and model with and without all-wheel drive. You may find that you don't like how all-wheel-drive feels. You may also want to try various makes and models so you can experience the differences in different AWD systems first-hand. From there, you can make an educated purchase online or locally. When it comes to buying a new or used vehicle, knowledge is power. Now that you understand how all-wheel-drive works, the next step is seeing if it's the right choice for you.