All Wheel Drive & Four Wheel Drive Explained

Four wheel drive (4WD) and all wheel drive (AWD) are very similar but they are not identical. Many people do not really understand the difference between the two and use them interchangeably. This is understandable because it is a tricky concept to grasp. Yet, it is important to know the difference between the two, especially if you are investing into one of these vehicles for a specific purpose, whether it’s off-roading or driving in the snow.

Before we discussed the basics of the drivetrain in 2 wheel drive (2WD) vehicles in our What You Need To Know About 2 Wheel Drive article. If you need some background on the basics, we suggest you go back and read the previous article before continuing this one. If not, let’s get started on AWD and 4WD vehicles.

Parts of All Wheel Drive & Four Wheel Drive Vehicles

First let’s cover the parts that are found in these drivetrains.

Transmission
This plays the same role with 4WD/AWD drivetrain compared to 2 wheel drivetrains. It connects directly to the engine and transfers the power that is sent from the engine to the wheels. Transmissions are an essential component of a vehicle, if you find yourself needing to replace your transmission to save your vehicle, check out a used auto part store. My Auto Store is a great place to purchase used transmissions online. They also offer free shipping from coast to coast in the United States!

Differential
They have the same function in AWD/4WD vehicles as they do in RWD vehicles. Except 4WD cars come with a locking differential on the front axle, these basically lock the two front wheels together forcing them to the same speed regardless of what wheel loses traction. Some AWD vehicles have 4WD capabilities that allow the driver to manually lock the differentials and give equal amounts of power to all wheels.

Transfer case
It allows the front two wheels to go different speeds than the back two. It takes power from the transmission and distributes it to 2 wheels or all of the wheels. In AWD it allows a set of wheels to receive more power when they begin to slip or lose traction. In 4WD it locks the front and rear axles together, so it gives the same amount of power to the front and back set of wheels. This forces the wheels to move at the same speed. 4WD cars also have low gear options, lower gears allow you to send more power to the wheels while going lower speeds.

Note: Full-time AWD and 4WD have an extra center differential built into the transfer case to send different amounts of power to the front and back set of tires when it is needed, unlike part-time AWD and 4WD systems. Full-time 4WD also has a locking center differential that can be engaged to force the front and back set of wheels to turn at the same speed.

Drive Shafts
There is a front and rear drive shaft, they connect the transfer case to the front and rear differentials with universal joints (u-joints).

All Wheel Drive

In AWD vehicles the engine power is usually sent to one set of wheels and when the axle starts slipping the power is diverted to the other axle to find more traction there. It is more common for the vehicle to be in FWD or RWD most of the time until there is slippage, then the other wheels receive power; this is called part-time AWD. There is a full-time AWD where all the tires are consistently receiving some percentage of power, usually one set of tires will receive most of the power but a smaller percentage will always be sent to the other set of tires. They occasionally get little boosts of power depending on if any wheels begin slipping. An AWD full-time system can be found in AWD Subaru’s.

Four Wheel Drive

4WD systems can be full-time, meaning that it stays in 4WD the entire time it is driven, this means there is never a 2WD option and some amount of power is sent to the all the vehicle wheels, at all times. It is very similar to full time AWD except, as stated before, it has locking differentials. This is why it is okay to drive full-time 4WD vehicles on any surface but you cannot drive part-time 4WD vehicles in 4WD mode on regular roads because the wheels do not change speeds.

The driver can switch between 2WD and 4WD in part-time 4WD systems. As we stated before, it is important to note you cannot drive in 4WD on dry pavement with part-time systems; this could ruin the drivetrain. 4WD modes on part-time systems are really for off-roading or slippery conditions. Using the part-time 4WD on regular surfaces causes excess wear and tear to the tires and causes drivetrain binding to occur.

All Wheel Drive & Four Wheel Drive Versus 2 Wheel Drive

AWD/4WD sounds like the better option, more traction, more control and more safety. Yet, these drive trains have their downfalls. Unlike 2WD cars, they are more expensive due to the enhanced complexity of the design, there are many more parts involved than in 2WD vehicles. Not only are they more expensive to buy, they are going to be more expensive to repair. Especially bigger car parts like engines are more expensive in these vehicles, which is why used engines are a better option if you need to repair your vehicle. There are many car part stores you can shop at but it is much easier and cheaper to buy used parts online from My Auto Store!

Due to the added parts, this means the car has more weight to it, causing the fuel economy to drop. Also, when you drive on all four wheels consistently, they wear down the tires faster than they would on 2WD automobiles. All this added together shows one thing, they are more expensive than 2WD systems.

It seems like the smart move would be to get a part-time system. This way you or your vehicle can decide when 4WD/AWD is necessary, otherwise the vehicle can stay in 2WD. If the roads are smooth and dry, 2WD works just fine if you are just driving to work or the store. AWD/4WD does not need to be engaged unless the road is slippery, uneven, you are off-roading or if you want that performance boost to impress those around you.

So, this brings the question: what one is better 4WD or AWD? The answer simply depends on where you live and what you want to use your vehicle for! Check out Is 4WD or AWD better for Off-Roading? to see what type of drive train system you should get.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s