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Volvo: Safety Beyond the Star RatingsWhat’s the Difference Between AWD, 4WD, RWD, and FWD?
To help with understanding wheel drive, we go through the specifics of front-wheel drive, rear-wheel drive, all-wheel drive, and four-wheel drive.Explaining Wheel Drive in a Car
Back in the day, as in pre-1970s, understanding wheel drive was somewhat easier than it is today. At that time, most vehicles were rear-wheel drive (RWD) with four-wheel drive (4WD) available on trucks. But times have changed. The back-to-back oil and fuel crises of the 1970s led drivers of big American cars to the likes of Honda and Toyota with their little front-wheel drive (FWD) vehicles that offered better fuel economy.
By the 1990s, the majority of vehicles sold stateside had dropped RWD in favor of FWD. Jump ahead another 30 years to the present day and all-wheel drive (AWD) has become increasingly common. With the influx of electric vehicles (EVs), we’re also seeing all manner of clever individually powered wheel drive. So, to help with understanding the drivetrain, powertrain, and everything in between, we’ll take a deeper look at the various wheel drive systems.
What is Rear-Wheel Drive?
Describing a vehicle as rear-wheel drive means the engine power is routed to the rear wheels only. A driveshaft, that spins in concert with the motor, runs from the engine up front down the middle to a differential out back. That differential, a housing filled with gears, redirects the power provided by the driveshaft to both rear wheels via axle shafts.
For more on how a drivetrain and powertrain differ, check out this explainer article. Benefits of RWD include better balance front-to-rear. With the engine up front and rear axle assembly out back, the weight of the powertrain is more evenly spread out compared to a FWD vehicle.
This has the effect of more satisfying handling as the front wheels are only responsible for steering while the rear wheels can stay focused on putting power to the road. It’s one reason that performance cars – Ford Mustangs, Mazda Miatas, and so on – continue to use this setup today. Additionally, hard acceleration is more controlled in a RWD vehicle as torque steer is generally not a thing. However, the added mass of this configuration leads to higher fuel usage and manufacturer costs versus FWD. Which is part of the reason so many vehicles made the switch in the ‘80s and ‘90s.
What is Front-Wheel Drive?
As it sounds, front-wheel drive means the front wheels receive the rotational power provided by the engine. By eliminating the drive shaft and rear differential, manufacturers can shed weight and improve cabin packaging over a RWD layout. Less weight helps improve fuel economy and without the need to make room for a driveshaft and associated rear-end drivetrain components, there is more interior space for passengers and cargo.
Typically, front-wheel drive vehicles will have the engine mounted transversely, or sideways, with the transmission right behind it and axle shafts running to both front wheels. That packaging efficiency comes with the downside of torque steer. Torque steer is the sensation of your steering wheel pulling left or right under acceleration. It’s due to the front wheels being responsible for both steering and power delivery.
An upside to a FWD configuration, versus RWD, is that it makes driving in slippery conditions less stressful. With the weight over the front wheels and the sensation of understeer instead of oversteer, most drivers will find a FWD vehicle moves better through rain and snow. Of course, AWD and 4WD are even better when it comes to driving in slick conditions.
What Does All Wheel Drive Do?
Though automakers like Subaru and Audi have been selling vehicles with all-wheel drive for decades, this four-wheeled configuration has become increasingly popular across the industry in the past 10 or so years. Some versions of AWD, like the Subaru design, send power to all four wheels constantly or “full time”. In other cases, like on a Honda, the AWD system automatically engages the rear wheels when conditions warrant it, but otherwise only the front wheels are powered.
Conditions that warrant engaging all four wheels would be when wheelspin is detected. By disengaging AWD in normal conditions, the vehicle can enjoy slightly better fuel efficiency as the parasitic drag of spinning all four wheels is eliminated. These modern AWD systems also feature a drive mode selector that allows drivers to select from pre-programmed settings tailored for conditions like snow or sport.
In everyday vehicles like a Toyota Camry or Kia Telluride, AWD is generally used as a helping hand in the rain and snow. More recently, high-performance cars like the BMW M3 have employed AWD to improve traction under hard acceleration and handling during aggressive maneuvers. With some 500 horsepower on tap, it helps to have all four wheels putting power to the ground. For something more extreme, check out these wild desert racing exotics that take AWD to an entirely different level.
It’s worth noting that a FWD or RWD vehicle with a good set of winter tires, which we cover here, will offer comparable snowy road handling to an AWD vehicle with all-season rubber. This can save you money as AWD usually adds cost to the price of a new vehicle. Those who need serious winter weather handling should read through this list of the best vehicles for driving in the snow.
How Does Four-Wheel Drive Work?
Like AWD, a vehicle with four-wheel drive can route engine torque to all four wheels for better traction. The difference is that 4WD, or 4×4, is typically defined as a part-time system that requires the driver to engage and disengage it as needed.
These systems are most common on pickup trucks and off-road focused SUVs like a Jeep Wrangler. Under normal conditions, these vehicles are RWD but when more traction is needed, the driver can use a separate transfer case to engage the front wheels.
The other difference between AWD vs 4WD is that when 4WD is engaged, the individual axles spin at the same speed. If you drive a vehicle with 4WD engaged on dry roads, the axles will bind when turning as the inside wheel will turn slower than the outside wheel. This causes a disconcerting vehicle hop that is best avoided. It’s why AWD is so much more prevalent than 4WD. The latter system is intended for very low traction conditions like off-roading and deep snow or sand.
Are Electric Vehicles All-Wheel Drive?
Like gas-powered vehicles, EVs come in FWD, RWD, and AWD configurations. However, the inherently tidy packaging provided by an electric motor allows for some clever applications. While many modern AWD systems utilize torque vectoring to increase or decrease the amount of twist applied to an individual wheel, some EVs take this to another level with individual motors powering each wheel. The Lucid Air Sapphire is one such vehicle.
It features one electric motor up front, to power those wheels, and two electric motors out back. Each of the rear motors can apply positive or negative torque independently. That means the outside wheel can be powered up while the inside wheel is slowed down to help rotate the car more crisply. This triple-motor AWD design, here applied to a luxury sedan, adds up to 1,200 horsepower and a 0-60 mph blitz of under two seconds. Pretty cool.
Editor’s Note: This post was originally published in December 2016 and has been completely revamped and updated for accuracy and comprehensiveness.
Rear drive more complex? Front and rear drive both more balanced? Front easier to service? You’re joking, right?