Electric vehicles are ushering in the return of rear-wheel drive. Here's why.
Over the past 40 years, front-wheel drive (FWD) has become the dominant layout for everyday autos. And for good reason. For a car designed for safety and efficiency, FWD offers quite a few advantages over rear-wheel drive (RWD). For a front-engine car, having the front wheels driven means no bulky driveshaft taking up room in the cabin. That means more room inside for passengers and cargo.
Omitting that drive shaft also potentially saves weight, which helps improve fuel economy. However, the most significant factor has proven to be safety and low-grip controllability. Front-drive cars are simply easier to drive — or perhaps it's better to say that they're harder to crash.
While front-wheel drive cars have been a fixture of the automobile industry since its very inception, they only came to really dominate the market here in the U.S. after the big fuel economy push in the 1970s. Since then, they've taken over the industry, with only a few sports and luxury cars staying true to RWD.
Now, there are early signs that the trend may be reversing. The single-motor configuration of every Tesla, meaning theModels 3 and Y,plus theCybertruck, are all RWD. Volvo also made headlines when it changed its electricXC40 Recharge to RWD and then doubled down by designing its upcomingEX30 to be RWD, as well.
While AWD is still available as an option, RWD is now the default configuration for those two Volvo EVs. For a safety-minded company like Volvo that had been developing front-drive-based cars for decades, it was a fascinating move. Clearly, when it comes to the capabilities and potential of an electric platform, RWD is starting to make a lot of sense again.
FWD vs. RWD: The physics of driving
Let's take a quick look at the physics of FWD vs. RWD. It's best to keep in mind the classic traction circle when thinking about this, which is a way to visualize the maximum amount of grip offered by a tire. You can use that grip for maximum acceleration, maximum braking, or maximum turning. But when you start to mix those actions — turning while accelerating or braking, for example — you must give up grip in one direction or another.
In other words, if you try to accelerate full throttle while turning, whether you’re in a FWD- or RWD-based car, you're probably going to run out of grip, and that could lead to a bad time.
In a RWD car, the front tires handle all the turning duties while the rear tires handle all the accelerating, which in theory means more overall performance. The problem is what happens when you try to do too much at once. Imagine accelerating too hard out of a corner in a RWD car. In this case, the rear tires generally lose grip first, which can result in the car spinning quickly. If you're an experienced driver, this can be arecipe for a good time.
If, however, you're a bit less experienced, it can be a recipe for a disaster.
Now imagine accelerating too hard out of a corner in a FWD car. In this case, the front tires generally lose grip first. Instead of the car spinning, the nose simply starts to slide wide. To catch this, typically all you need to do is lift off the throttle. The front tires will regain their grip, and the car will again resume turning like nothing happened.
While this behavior is a lot less fun than RWD, it is safer and, again, more predictable for rookie drivers. It does have some drawbacks, though. Because you're both accelerating and turning through the front wheels, those tires are doing double duty. The rear wheels, meanwhile, are just along for the ride.
Overall, the decision between RWD and FWD is a trade-off between fun performance and safe efficiency. For companies interested in safety, that has made it an easy choice when designing a new car. But the assets and capabilities of EVs are starting to change that equation.
RWD for acceleration
To look at one of the primary advantages of RWD, you need to move past the traction circle and move into some basic physics. In essence, a tire with more weight applied to it will provide more grip.
And what happens when you accelerate? The car's weight shifts backward thanks to inertia. This, then, gives the rear tires more grip. When most FWD cars were making less than 150 horsepower, as was the norm 20 years ago, this wasn't a big deal.
Today's EVs, though, make a lot more. The single-motor, two-wheel-drive Volvo EX30 makes 268 horsepower. According to John Lundegren, engineering manager at Volvo and tech lead for the EX30's driving experience, that simply wouldn't have worked going through the front wheels.
"On the EX30, specifically, we have quite a lot of power, over 200 kilowatts of power,” he said. “And if you have that, you basically have to have it in the back to get the traction you need. So the traction is on the rear wheel."
That was a primary reason why Volvo opted to put the motor in the two-wheel-drive EX30 at the rear. But, Lundegren says, a RWD configuration allowed Volvo to maximize the available grip, as well.
"It also comes with another benefit, which is that you separate the steering from the powered axle,” he said. “So you get better steering and a better feel for the driving experience."
But what about the risk of spinning the car from a lack of grip? That's where modern technology enters the equation.
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Stability control
Every new car on American roads today must have some form of electronic stability control, which can actively apply the brakes on individual corners of the car to keep it from spinning out when a loss of control occurs.
This is combined with traction control, which cuts power to wheels that are spinning under acceleration. In the 1970s, when FWD cars began to become the norm, traction control was an extremely rare thing and stability control was decades away. The addition of these systems has made RWD a viable option again.
The switch to electrification makes these systems even more effective. On cars with internal combustion engines, traction control usually works by either automatically closing the throttle or even cutting the spark on the engine. Either solution is simple and effective, but neither offers the finesse and quick response offered by electric motors.
With electric motors, the amount of power generated has nothing to do with physical things like throttle cables or, indeed, sparks that cause vaporized fuel to explode. Because of this, traction and stability control systems on EVs can react far more quickly to address spinning wheels or spinning cars.
The capability of these systems makes RWD possible in a car like the EX30, Volvo's Lundegren said. That's especially true when driven on low-grip surfaces like glare ice, where the company did extensive testing.
"You have quite a lot of power from these engines, so if you wouldn't have this spin control, you would need to be very, very gentle with the throttle,” Lundegren said, referring to driving the car on ice. “Otherwise you would spin around directly. I would say just turning the systems off for regular customers would make the car impossible to use."
So although a rear-drive car might be less stable in some situations, advanced stability and traction control systems make up for that, ensuring that even new drivers always stay in control.
What about regen?
Regenerative braking, particularlyone-pedal driving, is a way of slowing an electric or hybrid car down without using the brakes. Instead, the electric motor is used as a generator, providing resistance that slows down the car.
This not only saves you brake wear but also significantly extends the range of the car by providing a charge into the battery.
Consider what we learned above about inertia, about how an accelerating car will have more weight and grip at the rear wheels. That works when decelerating, too, but in reverse. A car that's braking has more grip at the nose, which is why virtually every car on the road has bigger, more powerful front brakes.
Given that, it seemingly makes sense to have the electric motor up front so that the car could use maximum regenerative braking. But, Lundegren says, that's not an issue.
"That is not a big factor, not what we have seen, at least," he said. According to Volvo's testing, there's plenty of grip at the rear wheels to meet the EX30's regenerative braking needs.
Compared to all-wheel drive
We've primarily been talking about FWD vs. RWD, but all-wheel drive is also quite common in electric cars, usually provided by a pair of electric motors, one at the front and another at the back.
AWD theoretically offers the best solution, making maximum use of grip of all four tires under acceleration while providing improved front regen under deceleration.
But Lundegren says that in dry conditions, at least, the AWD EX30 doesn't behave significantly differently than the RWD model. That car only engages the front motor when the rear loses grip, using a clutch at the front axle to quickly bring the front motor into use when needed.
"If you're accelerating a bit hard in a roundabout or a curve taking up speed, then you will have micro-slip, and then you will have the front motor engaged," he said. "But I would say if you're just cruising, normal speed, gently accelerating, then it's only the rear motor that is activated, and the benefit of that is that it's not using excessive consumption."
The extra power of the front motor certainly makes for a quicker car, and in especially low-grip situations like in snow and ice, there will be greater confidence from the dual-motor setup. But it comes with a loss of range and additional cost.
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Other advantages
Acceleration, deceleration and stability control are the major factors when we're talking about RWD vs. FWD electric cars, but the unique layout and design of EVs help change the equation, as well.
For one thing, when we're talking about electric cars, there are no more driveshafts to worry about. Electric motors are so small that they can be placed exactly where they're needed. As a result, rear-drive EVs typically position the motor directly between the rear wheels.
This means no bulky driveshaft to run from the engine up front to the driven wheels out back. This keeps the cabin layout clear for a flat floor, with lots of cargo and legroom for your passengers.
EVs also tend to have a more optimal weight balance. While positioning the electric motor between the driven wheels helps, the bigger factor is the battery pack.
Battery packs are upwards of 25 percent of the weight of an EV, and they tend to be wide and flat, making up the floor of the car. Because this weight is spread out, the weight of the car is more evenly distributed across all four wheels.
And finally, there's the crucial fun factor. RWD cars are, simply, more enjoyable to drive hard. They accelerate more quickly and tend to offer better handling and more grip. When it came to designing the EX30, fun was indeed a priority for Lundegren and the engineers at Volvo: "It's actually an important part of the development of this product. It's our smallest car, we have the shortest wheelbase, it's got plenty of power, so we really wanted to keep it agile, fun to drive."