Why is rear-wheel drive making a comeback with EVs?

Electric cars are taking a step back in time to move forward into the future. But why?

While most small cars and SUVs have made front-wheel drive powertrain configurations the norm, dedicated electric cars are reverting back to the traditional rear-drive layout.

Among the EVs on sale in Australia at the moment there is still a mix of the old as models like the Nissan LEAF, Hyundai Kona Electric and MG ZS EV are battery-powered adaptations of conventional models that utilise the space normally reserved for a petrol engine up front and a petrol tank at the rear to fit the electric motor and battery pack.

But models that have been created as purely electric cars from the outset, such as the BMW i3 city car, the Tesla Model 3 and the upcoming Hyundai IONIQ 5 and Kia EV6, have adopted the new train of thought, placing the primary engine at the back of the vehicle to drive the rear wheels.

“Electric cars have opened new ways of thinking for our engineers and designers,” said Hyundai Australia’s general manager of public relations, Bill Thomas.

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“The simple fact that electric motors are physically smaller than petrol engines has allowed them to be positioned in the rear of the vehicle without compromising cargo space.

“In fact, it’s quite the opposite as we can now utilise the significant area where the engine would normally be for additional luggage room.

“From a packaging point of view, it’s a win-win situation.”

More than that, the smaller electric motors – plus the fact that there is no additional requirement for ancillaries like radiators in front of them – means the powertrain can be pushed to the extremities of the vehicle, which subsequently increases the wheelbase of the vehicle for more interior space.

It also improves the effectiveness of the frontal crash structures and the ability for the car to absorb energy in an impact, and limits the damage to expensive components for better repairability.

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A longer wheelbase also improves the overall stability of the vehicle, while separating the functions of the front and rear axles brings even more dynamic benefits.

In front-wheel drive cars, the front tyres have to cope with the forces of both steering and traction which inherently compromises both functions.

For starters, with unequal-length drive shafts, front-drive cars have a tendency to torque-steer under heavy acceleration – the sensation of the wheel tugging to one side when you floor it from a standstill or out of tight corners.

Secondly, because the front hubs are linked to both the drive shafts and steering arms they are restricted in the amount of steering lock available and therefore have quite large turning circles, which makes it difficult to manoeuvre around tight spaces.

Also, with the heaviest components all located in the one area, it is almost impossible for front-drive cars to achieve an optimum 50:50 weight balance, which means they tend to understeer – where the front tyres lose grip – during hard cornering.

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By positioning a smaller, and lighter, electric motor in the back of a battery-powered vehicle it allows the rear axle to be dedicated solely to traction while the front is focused on steering.

Essentially, it is more effective to push a vehicle (rear-drive) than it is to pull it (front-drive) while having more weight across the rear axle naturally improves traction under acceleration.

At the other end of the vehicle, rear-drive electric cars can have longer steering arms for greater manoeuvrability and better cornering feel and responsiveness.

Even as most dedicated EVs are also offered with twin-motor all-wheel drive configurations, it’s a better solution than a conventional combustion-engined layout as the motors do not need to be linked by a complex gearbox and drivetrain system.

So, there you have it. There are plenty of good reasons why electric cars are taking a step back to move forward.