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The shape of the electric motor and, more importantly, the electric cars that power may be to change. To CES 2025electric motor manufacturer Donut Lab has developed its second-generation in-wheel drive units. The new engines promise great power and torque with little in the way of weight and, like the company’s namesake, a big hole in the middle.
The design of the EV inherits much of the architecture of the combustion car: There is an engine (sometimes two or three) somewhere in the body of the vehicle that is connected to the wheels via a drivetrain . In-wheel electric motors promise to reduce and move those components into the wheel arches, freeing up space in the cabin for people and cargo. However, there is one major problem that Donut thinks it can overcome: the motors are very large and very heavy.
Donut Lab’s second-generation donut engine squeezes into a 21-inch circle, promising up to 630 kilowatts (845 horsepower) and 4,3000 newton-meters (3,171 pound-feet of torque) per unit. Before you get too excited about that torque figure, consider that the torque of the “normal” electric motor is usually measured at the rotor before multiplying by a single speed box that donuts don’t have. Therefore, while the torque output of the 21-incher is certainly impressive, it is not quite a quantum leap over, for example, a unit of Tesla.
These large loops could be the future of electric motor design.
However, where the donut-shaped engine shines is its weight – the arch nemesis of every EV engineer and designer. The 21-inch unit is said to weigh just 88 pounds (40 kg) or about one-third of a traditional rotor-stator electric unit. Less weight means more range. Of course, you need two motors per “axle” (unless you’re building a trike), but with the additional weight savings from cutting out half-shafts, CV joints and other transmission components, Donut thinks whose hubless wheels can save you hundreds of pounds. Less weight means more range, which is good. Alternatively, more motors for the same or less weight means more precise control and more total power, which is really good!
The engine manufacturer also claims that its engines are up to 50% less expensive to manufacture, saving around 120 parts along the way. That could make for less expensive cars on the road. Moving the engine in the wheel arches, also saves space in the chassis that can be reallocated for cargo, passengers, more batteries or experimental aerodynamics. (Think about Jaguar i-Pace o Polestar 3the front wings, but even wilder.)
Donut’s design integrates the motor and its cooling hardware into the wheel rim, saving weight and freeing up space in the chassis.
Of course, the elephant in the room is that while Donut Lab wheels are lighter than previous in-wheel motors, they are still heavier than conventional wheels. More importantly, they add pounds to the worst place a car can gain weight: under the suspension. Gaining unsprung mass, as it is known, has a much greater impact on performance and comfort than comparable mass gained in the vehicle chassis and rotating mass is even harder to argue with. With more than 80 extra ell-bees per wheel, there is an impact on braking, handling and ride quality, although how much remains to be seen.
Alongside the 21-inch automotive wheel, Donut Lab also introduced a 21-inch wheel efficiency-focused semi-truck version that boasts a lower operating RPM, 200 kW and 2,212 lb-ft (3,000 Nm) per wheel. The line will also include a 12-inch (15 kW) scooter motor and a 120 mm (3 kW) drone motor. Donut’s 150 kW, 17 inch motorcycle engine is already in use on the road for a few. electric bike boutiqueso the probability of seeing this technology on a car in the future is better than you might think.
