What are in-wheel traction systems

In-wheel traction systems are an aggregate of electric motors placed directly in the wheel of a motorized vehicle and they belong exclusively on electrified vehicles. Basically, instead of having a motor placed under the hood, in the center or in the rear of a car, in-wheel drive systems are placed directly in at least two of an EVs wheels.

Because an in-wheel electric motor turns only one wheel at a time, at least two such electric motors are required for the vehicle to move symmetrically; in other words, to power both the left and right wheels at the same time without losing control. This type of traction system, although not used very often in series production vehicles, has multiple benefits, but also some challenges associated, which we'll discover together.

An in-wheel electric motor is smaller than even a conventional electric motor, let alone an internal combustion unit. This makes in-wheel systems extraordinarily efficient, since they drive the wheel directly, without the need of using additional components, such as drive shafts, and thus, all the power reaches the wheel and little to nothing is being wasted.

Additionally, precision and response times, already very good on an electric motor, become even quicker.

In-wheel systems, an invention from over a century ago

The first traction systems with in-wheel electric motors were developed in the late 19th century by a Viennese company called Lohner & Co, which also manufactured the world's first hybrid car. This car had an ICE engine, as well as a traction battery that powered four independent electric motors placed in the wheels of the car.

Photo source: BMW

The father of in-wheel drive systems is none other than Ferdinand Porsche, who needs no further introduction in the world of automotives. Maybe ironically, no current electric Porsche model uses in-wheel drive systems, but who knows where the evolution of battery-powered cars will take us.

Currently, BMW is one of the manufacturers that actively works on the improvement of in-wheel drive systems through its startup called Garage. The system, developed alongside a Munich-based company called DeepDrive, promises better performance and also better range compared to current electric models.

At the same time, one of the few series electric motors that currently uses this technology is the Mercedes-Benz G580 EQ, which uses four electric motors for each of its four wheels, allowing this SUV to achieve better performance, as well as remarkable mobility on and off road. Basically, thanks to the independently driven electric motors, the car can steer much sharply and even pivot on the spot.

Neue Klasse models from BMW and the Renault 5 E-Tech Turbo 3E will also employ in-wheel electric motors to offer better efficiency, performance and safety.

Advantages of in-wheel drive systems

Among the benefits of using in-wheel drive system sit the improved efficiency and the performance potential, but also increasing the safety level that such a traction system could offer.

Since at least two of the four wheels of the vehicles are powered by independent motors with instant response, the stability and maneuverability are also exponentially better. This helps offer a more pleasant and precise dynamic driving, as well as better traction control to keep an optimal grip in case of emergency.

Furthermore, placing these electric motors at the wheel frees up space under the bonnet or the boot for extra storage space and even a larger battery, while the vehicle's center of gravity is also improved.

Another potential benefit is eliminating the parts that are usually exposed to wear and tear and that can break, such as drive shafts, which improves long-term reliability and can cut back on maintenance costs.

Challenges associated with in-wheel traction systems

There are some well-founded reasons why these traction systems didn't already reach series production, especially on more affordable models. One of it is the complexity associated with in-wheel drive systems. One of the drawbacks is that in-wheel electric motors are not supported by a car's suspension system, since they are placed below it. The rims, the tires and most of the braking system are located below the suspension.

By adding in-wheel drive, the weight increases, while comfort and maneuverability can both be negatively affected.

Photo source: Honda

Another thing to consider is the exposure to the elements, such as water, dirt or mud, but also other possible obstacles or objects that the wheel hits during driving. Although the rims and tires are designed in such a way to be a little elastic and deal with the shocks, motors don't enjoy the same properties and hitting the sidewalk a bit stronger or any obstacle hit with the wheel could lead to a more costly repair compared to a traditional car.

In-wheel motors are more complex and more expensive to manufacture and implement on a car for the first time. Even though in the long term, using such a traction system accordingly could lead to lower costs, manufacturers are the ones that have to account for the high initial investment in order to optimize the chassis and adapt the overall fell of the car.

Also, installing a proper cooling system for this kind of electric motor, required even for EVs, is more difficult when we are talking about in-wheel motors, which are more compact and space-constrained than conventional models.

In-wheel traction systems conclusions

Maybe one day we will see more affordable electric vehicles sporting in-wheel traction systems that will improve on the stability and driving efficiency, but for now, this seems like a far-fetched dream. Manufacturers will seek new solutions to improve the performance of EVs and in-wheel motors are a potential solution, should the industry overcome existing challenges.

Photo source: Nissan