The shape of the electric motor and, more importantly, the electric cars that they power may be about to change. At CES 2025, electric motor manufacturer Donut Lab rolled out its second-generation in-wheel drive units. The new motors promise big power and torque with very little in the way of weight and, like the company’s namesake, a big ol’ hole in the middle.
The way EVs are designed inherits a lot from combustion car architecture: There’s a motor (sometimes two or three) somewhere in the vehicle’s body that’s connected to the wheels via a drivetrain. In-wheel electric motors promise to shrink and move those components into the wheel arches, freeing up space in the cabin for people and cargo. However, there’s one big problem that Donut thinks it can beat: motors are very big and very heavy.
Donut Lab’s second-generation donut-motor squeezes into a 21-inch hoop, 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 “normal” electric motor torque is usually measured at the rotor before it’s multiplied by a single-speed gearbox which the donuts don’t have. So while the 21-incher’s claimed torque output is certainly impressive, it’s not quite a quantum leap over, say, a Tesla drive unit.
However, where the donut-shaped motor 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 a third of a traditional rotor-and-stator electric drive 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 ditching half-shafts, CV joints and other drivetrain components, Donut reckons that its hubless wheels can save 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 motor maker also claims its motors are up to 50% less expensive to manufacture, saving around 120 parts along the way. That could make for less expensive cars down the road. Moving the motor into the wheel arches also saves space within the chassis that can be reallocated for cargo, passengers, more batteries or experimental aerodynamics. (Think the Jaguar i-Pace or Polestar 3‘s front wings, but even wilder.)
Of course, the elephant in the room is that while Donut Lab’s wheels are lighter than previous in-wheel motors, they’re still heavier than conventionally driven wheels. More importantly, they add pounds to the worst place a car can gain weight: below the suspension. Gaining unsprung mass, as it’s known, has a much larger impact on performance and comfort than comparable mass gained in the vehicle’s chassis and rotating mass is even harder to wrangle. With 80-plus extra ell-bees per wheel, there’s bound to be some impact on braking, handling and ride quality, though it remains to be seen how much.
Alongside the 21-inch automotive wheel, Donut Lab also showcased an efficiency-focused semi truck version of the 21-inch wheel boasting a lower operating RPM, 200 kW and 2,212 lb-ft (3,000 Nm) per wheel. The lineup will also include a 12-inch scooter motor (15 kW) and a 120mm drone motor (3 kW). Donut’s 150 kW, 17-inch motorcycle motor is already in use on the road for a few boutique electric bikes, so the odds of seeing this tech on a car in the future is better than you might think.
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