The Finland-based company's in-wheel motor serves up 650 kilowatts of power
Lawrence Ulrich is an award-winning auto writer and former chief auto critic at The New York Times and The Detroit Free Press. 5hp 3 phase
Donut Lab's automotive hub motor on display at their CES booth in January 2025.
In-hub wheel motors are among the most tantalizing and yet elusive of electric-vehicle technologies. And now, after decades of failures and near-misses, a donut-shaped electric hub motor was among the sweetest offerings at the recent CES show in Las Vegas.
The motors come from Donut Lab, a spin-off of Finland’s Verge Motorcycles, which uses Donut’s first-generation hub motors in its electric two-wheelers. Donut Lab claims these wild-looking, hole-in-the-middle motors deliver the highest density of any hub motors yet, in varying applications for cars, motorcycles, scooters or drones. The company’s lineup includes a 53-centimeter diameter (21 inch) model—ideal for today’s mammoth automotive wheels and tires—with a claimed 650 kilowatts (844 horsepower) and 4,299 Newton-meters (3,171 pound-feet) of torque. Before you imagine drag-racing every Tesla in sight, note that torque figure is measured at the rotor, so the figures at the wheel itself would be some what lower. Still, a pair of these motors, or up to four in all-wheel-drive vehicles, will generate enough torque to satisfy the biggest performance junkies.
More importantly, these in-wheel hub motors, which spin a wheel directly because their rotor is part of the wheel, have intriguing potential to improve performance and vehicle packaging, while greatly reducing moving parts and maintenance. But t his longtime automotive goal remains unrealized: Startup Lordstown Motors attempted it with its four-motor Endurance pickup truck, before that start-up flamed out in a flurry of lawsuits, SEC charges, and fraud accusations.
Going back 125 years, Ferdinand Porsche, whose son Ferry would later found the famous sports-car maker, was already onto something at the 1900 World’s Fair in Paris. Porsche unveiled the Austrian-built Lohner-Porsche, an electric car with front wheel-hub motors that cranked out 1.7 kilowatts (2.4 horsepower), good for a top speed of 32 kilometers per hour (19.8 miles per hour).
Porsche is still patting its own back today, but what’s taking so long? For hub motors in automobiles, unsprung weight remains the chief drawback: Putting the mass of a motor inside a spinning wheel, an outboard location unsupported by suspension components, makes it fiendishly difficult to tune a vehicle for a smooth ride and responsive handling.
Donut Lab says its motors are light enough to overcome the problem. The company says its largest, 53-centimeter supercar-level motor has a 21-inch diameter, and checks in at a svelte 40 kilograms (88 pounds). Punching a calculator suggests a formidable power-to-weight ratio of 15.75 kW/kg, or 9.6 hp/lb. For a comparison, Lordstown’s hub motors, licensed from Slovenia’s Elaphe, weighed about 39 kilograms but generated just 81 kilowatts (110 horsepower) for a power-to-weight ratio of just 2.1 kW/kg. Donut’s preliminary numbers may prove optimistic, but the company claims nearly six times the Lordstown’s output at identical weight. The 40-kilogram “Dark Matter” motor in the four-seat Koenigsegg Gemera—a six-phase radial radial-flux design—makes up to 597 kilowatts (800 horsepower) and 1,250 Nm for a power-to-weight ratio of 14.9 kW/kg. But Koenigsegg’s Swedish creation is not a wheel hub motor, requiring an axle and other weighty drivetrain components to transmit power to the ground.
A Verge motorcycle being driven in Helsinki, Finland, on July 26, 2023 shows off the hub motor in the rear wheel.Vesa Moilanen/Sipa USA/AP
“Great unsprung mass has been the most important reason why everyone hasn’t used motors integrated with the tire in their vehicles,” said Marko Lehtimäki, co-founder and CEO of Donut Lab. “Through the torque and power density we’ve now achieved, the relative weight of the motor is so small that for the first time the unsprung mass is insignificant.”
Indeed, if weight inside wheels is an issue, these motors save it elsewhere, eliminating any need for bulky transmissions, driveshafts or axles. That in turn could help designers carve out more room for passengers and cargo, or to shrink a vehicle’s footprint while maintaining the same interior space. Hub motors also offer the promise of granular, millisecond-quick control over torque at individual wheels. That offers safety and performance advantages for not just performance cars but also most any application, whether it’s a family sedan, off-road vehicle or sports car.
Beyond motors, Donut Lab touted its modular, connectible system of batteries, computer controllers and software. And at CES, the company showed off a family of hub motors in various sizes and strengths. One version, designed for semi trucks, generates 200 kilowatts. A 43-centimeter (17-inch) motorcycle motor makes a healthy 150 kilowatts. Itty-bitty versions for scooters and drones include a drone motor that weighs just 1.5 kilograms, with a 120-mm diameter, but spins up 3 kilowatts.
3 phase ac motor Lawrence Ulrich is an award-winning auto writer and former chief auto critic at The New York Times and The Detroit Free Press.