EV Motors Explained: What kW, Nm and Motor Types Mean When You Buy an EV

How an electric car moves has very little in common with a petrol or diesel car. A combustion engine burns fuel in cylinders, needs to be revving before it delivers useful power and relies on a gearbox with several gears to stay in that range. An electric motor has one main moving part and makes a strong pull from a standstill, so a single gear is usually enough. That’s also why EVs come in several motor types with no equivalent in the petrol world, and the differences between them are bigger than most spec sheets let on.

Almost every EV on sale today uses a permanent magnet motor, and the type tells you less about the car than two numbers on the spec sheet, kW and Nm. Those decide how hard the car pulls, while kWh per 100 km decides what it costs to run. I’ll explain what they mean and where the motor types really differ.

Here’s the short version first. The table covers the three ways a rotor can get its magnetism, and the sections after it go through each one in plain English. Axial flux, a different motor shape, comes after that.

The abbreviations in the table are the ones you’ll see on spec sheets. PMSM stands for permanent magnet synchronous motor, and Audi and Porsche’s PSM and the IPM label (magnets buried inside the rotor) describe the same family. ASM, short for asynchronous motor, is the induction motor, and EESM, short for electrically excited synchronous motor, is the wound rotor.

How an EV Motor Works

An EV motor has two main parts. The stator is the fixed outer ring, wound with copper coils. The rotor is the part that spins inside it, a shaft with a magnetic core, and it’s connected to the wheels through a gear.

The battery supplies direct current (DC), but the motor runs on alternating current (AC), so a unit called the inverter converts one into the other. It feeds the stator coils in a sequence that creates a magnetic field rotating around the ring, and the rotor gets dragged along behind it. By changing how fast that field rotates and how much current flows, the inverter controls the motor’s speed and torque, and a reduction gear passes the power on to the wheels. When you lift off the accelerator, the motor can run in reverse: the wheels turn the rotor, the motor becomes a generator and part of the energy can flow back into the battery. That’s regenerative braking, and how much you get depends on the car’s settings, the driving conditions and whether the battery can accept the energy.

Motor types differ in one thing only, which is how the rotor gets its own magnetism. It can have permanent magnets built in, it can have magnetism induced by the stator, or it can be fed with electricity through coils of its own. The rest of the article follows from that choice.

What kW, Nm and rpm Actually Mean

Three numbers turn up on every spec sheet, and they’re linked. Torque, measured in Newton metres (Nm), is the twisting force at the motor shaft and it’s the shove you feel in your back when you pull away. Speed is measured in revolutions per minute (rpm), meaning how many full turns the shaft makes in a minute. For scale, a petrol engine idles at around 800 rpm and typically runs out of revs somewhere between 6,000 and 7,000 rpm, while BYD says its newest motor spins past 30,000 rpm.

Power, measured in kilowatts (kW), is how much work the motor does every second, and it combines the other two. The metric horsepower figure in brackets after it (PS) is simply 1 kW multiplied by about 1.36. Here’s the relationship:

Power (kW) = Torque (Nm) × Speed (rpm) ÷ 9,549

The 9,549 is just a unit converter. Physics wants the speed in radians per second and the power in watts, one rpm equals 2π ÷ 60 radians per second and 1,000 watts make a kilowatt, so the constant works out as 60,000 ÷ 2π, which is roughly 9,549. You can ignore it and remember that more torque or more rpm means more power. The table shows what happens to a motor that makes a steady 300 Nm as the revs climb.

Illustration of the formula, not a real car.

In a real motor the inverter, battery and cooling cap the power, so torque has to fall once the revs pass that point.

Spec sheets add one more complication, because wheels turn much slower than the motor. A single-speed reduction gear sits in between, often with a ratio somewhere around 8 or 10 to 1, so I’ll use 9 to 1 in the examples. It works in two directions:

Motor speed (rpm) = Wheel speed (rpm) × Gear ratio

Wheel torque (Nm) = Motor torque (Nm) × Gear ratio

For a typical tyre that’s about 2 m around, wheel speed in rpm is roughly the speed in km/h multiplied by 8.3. The table shows what that means for the motor.

Illustration with a 2 m tyre circumference and a 9 to 1 ratio.

Torque gets multiplied by the same ratio, so a motor making 300 Nm puts roughly 2,700 Nm through the wheels. That’s why a motor torque figure and the torque at the wheels are two different numbers, and I’d only compare cars that quote the same one.

What surprised me most when I started driving EVs was the acceleration. Picture an EV crawling along at about 20 km/h, where the table puts the motor at roughly 1,500 rpm, and you press the pedal. The motor can deliver a lot of torque almost immediately, without waiting to rev up and without the pauses of gear changes, as long as the tyres can put it on the road, so the car shoots forward like an arrow. A petrol car in the same spot needs the revs to climb first, because an engine typically makes its best torque well above idle, and that takes time. When the rev counter nears the red zone you have to shift up, the pull is interrupted and the revs fall back before they start climbing again. An EV skips all of that, which is why even a modest one feels quick away from the lights.

The kW on the spec sheet is also usually the peak. A motor makes heat, and cooling can only deal with so much, so after a short burst the software pulls the power back. The continuous power is what the system can sustain under given conditions, and cooling, ambient temperature, load and the carmaker’s control strategy all play a part. Few carmakers publish it, and BMW is one that gives a related number: its official technical data lists the iX3 50 xDrive at 345 kW (469 PS) rated and 170 kW (231 PS) as the 30-minute output. That figure describes the whole drive system and not the motor on its own, and every maker measures it in its own way. For a more extreme case, YASA, the motor maker owned by Mercedes, estimates that its 750 kW prototype could hold 350 to 400 kW, so roughly half. It matters on long motorway runs, steep climbs and when towing.

Permanent Magnet Motors Are the Default for Good Reasons

A permanent magnet motor has strong magnets, usually made with the rare earth metal neodymium, built into the rotor. The rotor spins in step with the stator’s rotating field, which is what the word synchronous in PMSM refers to. Adamas Intelligence, a market research firm, counted nearly 91% of the motor power in new passenger cars during the first half of 2025 as permanent magnet.

Adamas Intelligence, first half of 2025, weighted by motor power and including hybrids.

An earlier Adamas snapshot from June 2023 pointed the same way, with nine out of ten traction motors deployed that month using permanent magnets, although that counts motors and not motor power.

Carmakers weigh efficiency, size, cost, supply and coasting losses, and magnets win on the first two. Adamas says they’re up to 15% more efficient than alternative motor types and the most power-dense traction motors commercially available, so the same battery goes further, or a smaller and cheaper one does the same job, and the compact motor leaves more room in the cabin and boot. Cost and supply are where magnets lose points, which I come back to further down. Coasting losses depend on the design and the control strategy, and carmakers have several ways to reduce them.

Induction and Wound Rotor Motors Skip the Magnets

An induction motor has no magnets at all. The stator’s rotating field induces an electric current in the rotor, and that current makes the rotor magnetic and makes it chase the field. It costs less to build and it can spin with low losses when it isn’t driving the car, which is why you find it on the front axle of so many all-wheel-drive cars. The rear motor does the daily work, and the front motor only joins in for traction or hard acceleration. The all-wheel-drive Tesla Model 3 does this, and so does the Audi Q6 e-tron. My BYD Seal vs Tesla Model 3 comparison covers two cars built around that idea.

On its own an induction motor loses a few percentage points of efficiency in gentle driving, because the current that magnetises the rotor also heats it, and it’s usually bigger and heavier for the same output. That makes it a useful extra motor that steps in when you need more traction or power, because in a suitable design it can spin with low losses while it isn’t being driven.

A wound rotor motor, the EESM from the table, replaces the magnets with copper coils on the rotor. Current has to get into the spinning rotor somehow, and the common solution is slip rings, which are metal rings on the shaft that carbon brushes press against. Some designs transfer the energy contactlessly instead, using a rotating transformer, but that adds extra electronics. Where brushes are used they aren’t the worn brushes of an old 1980s power drill, since BMW says the brushes in its fifth-generation motor sit in a sealed space so the dust can’t escape, and carmakers design the assembly for long service life. A sliding contact is still a part that can wear, so I’d ask about it when checking the motor warranty. Because the car controls that current, it can adjust the strength of the field on the move or switch it off, which removes coasting drag. Renault is the most committed user, and Renault Group says it started selling them in volume in 2012. BMW says the iX3 50 xDrive uses an upgraded wound rotor motor at the rear and a new asynchronous motor at the front, and the Renault 5 sticks with the technology in all three of its power ratings, from 70 to 110 kW. The advantage is that the motor needs no permanent magnets, and the price is a more complex rotor excitation system and a rotor current that is a loss of its own, so efficiency depends on how well the carmaker manages it.

Axial Flux and Other Exotic Motors

The three motor types in the table differ in how the rotor gets its magnetism. Axial flux is a separate question: it describes the shape of the motor and the direction of the magnetic flux. Instead of the usual cylindrical design, where the rotor spins inside a ring, an axial flux motor is shaped like a flat disc, with the magnetic flux running parallel to the shaft. The axial flux motors Mercedes builds with YASA use permanent magnets.

Here the stator sits between two rotors, which gives more torque from the same amount of magnet and copper. YASA, which Mercedes-Benz has owned since 2021, built a prototype that shows how far the shape can go, and its numbers are in the table further down. Mercedes has started series production of an axial flux motor for the AMG GT 4-Door Coupé, which has three of them, and it lists the GT 63 at 860 kW (1,169 PS) with launch control active. Mercedes says one weighs around a third of a conventional motor with the same output. Unless your commute includes a launch control button, this stays a spectator sport for now, and my overview of EVs above €100,000 lists the alternatives at that price level.

Spinning faster is another way to get more power from a small motor, and BYD says its Super e-Platform motor, the one I mentioned for its revs earlier, is the first mass-produced design to go this fast. A high top speed lets a smaller motor deliver the same power, but it demands stronger bearings, careful balancing, good cooling and precise control, and the rev figure alone says nothing about efficiency. It runs on a 1,000-volt system, a step beyond the cars in my 800-volt EV overview. Two other designs are mostly a curiosity for buyers. In-wheel motors sit inside the wheel hub, which removes the driveshafts and gearbox but adds unsprung weight, the weight the suspension doesn’t carry, and in theory that can hurt ride and handling. Switched reluctance motors have no magnets and no coils on the rotor and are simple and tough, but they’ve historically been too noisy for passenger cars.

Power density, meaning kW per kilogram, is one way to compare these designs:

Power density (kW/kg) = Power (kW) ÷ Weight (kg)

Manufacturer figures that aren’t necessarily directly comparable, since the weight of a motor can be counted with or without parts such as the inverter, cooling and gearing. The YASA motor is a prototype and the BYD motor is in mass production.

A high figure suits a performance car. For a city car, cost, everyday efficiency, durability and size matter more.

What Real Cars Deliver and Why Rare Earths Matter

The table below puts five cars side by side to show how little the motor type says about output.

Peak figures from Renault, BMW and Audi for their own cars and from the evspecifications.com database for the two BYD models. Audi lists 350 Nm for the updated Q4 e-tron 40. The single-motor cars show one motor, while the BMW figures are the combined output of both motors, as listed on BMW’s technical data page.

The BYD Atto 3 and the Audi Q4 e-tron 40 have the same 150 kW and 310 Nm from the same type of motor, while the Renault 5 has a wound rotor motor rated lower at 110 kW and 245 Nm. Output comes from motor size, cooling, voltage and the limits in the software. The type decides other things, such as how the car coasts, what the motor costs and where its materials come from. The small BYD Dolphin Surf sits at one end of the table and the two-motor iX3 at the other, a car whose Gen6 drivetrain I went through in my BMW Neue Klasse deep dive.

Materials are where the story gets political. Rare earth metals such as neodymium and praseodymium go into the magnets, with dysprosium and terbium added to keep them strong when hot, and IEEE Spectrum, citing Adamas, puts the average at 1.2 kg of magnets per 100 kW of peak power. The metals, the alloys and the finished magnets are different steps in the chain, and China is strong in all of them. In June 2025 AlixPartners put its share at about 90% of rare earth metal alloy and magnet production, and Motor Finance Online reported that Europe sources 98% of its rare earth magnets from China. In April 2025 Beijing placed seven medium and heavy rare earths on its export restriction list, and by June the supplier association CLEPA said several European supplier plants had already shut down. Reducing that dependence is one of the main reasons for developing and using wound rotor motors.

What I’d Check Before Buying an EV

I’d start with kWh/100 km, because it reflects the whole drive unit and the car around it, and I’d treat the motor type as a tiebreaker. A permanent magnet motor is a safe default and a wound rotor is a perfectly good alternative. An induction motor on the front axle is a common way to add traction without a second magnet motor.

That number turns directly into distance, and motor efficiency is one of the things that moves it:

Range (km) = Battery capacity (kWh) ÷ Consumption (kWh/100 km) × 100

Illustration. It assumes all 60 kWh are usable, while real range depends on the usable capacity, temperature, speed and route.

One kWh/100 km looks like a rounding error, yet in this example it costs roughly 20 to 30 km of range.

I’d only pay extra for a second motor if I needed all-wheel drive or wanted the extra performance, and otherwise I’d compare the real range, price and performance of the single-motor version first. If I towed a caravan or drove long stretches at high speed, I’d ask about continuous power and cooling. 150 kW is enough for many family cars, such as the Audi Q4 e-tron and the Atto 3 in the table, but how a car feels also depends on its weight, gearing and the power available at the speeds you drive, so I’d take a test drive.

I’d also check how the warranty covers the motor and inverter and not only the battery, and my comparison of EV warranties in Europe is a good starting point, while the European reliability data shows how brands compare on faults. I wouldn’t pay extra for a magnet-free motor, because the supply security benefits the carmaker first, but I’d happily buy one if the rest of the car suits me. The motor type doesn’t decide consumption on its own either. The efficiency of the whole drivetrain counts, and so do weight, aerodynamics, tyres, speed and driving conditions, so a car with a magnet motor won’t automatically use less than one with a wound rotor. For most buyers, the motor type is less important than the car’s real-world efficiency, performance, warranty and price. Knowing the difference helps explain why two EVs with similar specifications can have different strengths. Battery chemistry deserves the same attention, and my LFP vs NMC guide covers that side while my ranking of electric SUVs by Euro NCAP child safety covers that part of the checklist.