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BMW has started teasing a 4-Motor M-3 variant of their hot sports sedan. Most high-performance cars currently for sale are 2-motor, with the fastest Tesla standing out as a 3-motor variant. With Gas, other than some interesting prototypes like the two-engine Oldsmobile Toronado (one of which I’d have loved to own, I owned the single-engine version years ago).
Why 4-Motors
We currently have 4-wheel drive and all-wheel-drive when talking about cars with 4-wheels each of which is powered. 4-wheel drive vehicles typically have ways to lock the wheel hubs and differentials so that you can better operate off-road, but the downside is you can damage your drive shafts because the wheels when locked up, don’t spin independently. Great for traction, but not great for longevity. All-wheel-drive vehicles typically don’t have lock up anything and use various methods to shift power from the wheels that don’t have traction to those that do.
4-motor electric cars are called “individual wheel drive” cars because each wheel has its motor. This is a more efficient way to get power to the ground. Still, you can also control each motor individually, applying different degrees of action control as needed to each wheel. Electric motors can be altered thousands of times a second, while gas motors are far less flexible. This means these four motors can be individually tuned for whatever traction they have and can be much more effective at torque vectoring, which can significantly improve cornering. You can also have the left and right-side motors go in different directions, allowing the car to pivot on its axis. This last is incredibly useful when parking in a tight parking garage.
Off-road and in snow or sand, this is also incredibly helpful because, coupled with the EV motor’s instant torque, you can much more easily keep from getting stuck.
The Downside To 4-Motors
Many of the 4-Motor concepts I’ve seen have had wheel-mounted motors, which have the advantage of easy maintenance of the motors and lower build cost but the disadvantage of significantly increased unsprung weight. Unsprung weight lowers traction, reduces ride quality, and can be hard on the components in the wheel. BMW appears to be planning to mount the motors in the car's body and then connect them with shafts to the wheels, which increases costs but should significantly improve handling for the car.
And speaking of costs, four motors, even though they’d be smaller, are still four motors, which increases the cost of assembly and maintenance and makes the cars more complicated and more complex to service. However, electric motors, compared to gas engines, are massively more reliable (the weak link in the EV is the battery, not the motor), offsetting this cost compared to a gas car.
Smaller, less powerful EV motors aren’t much smaller than their more powerful counterparts, so the adverse impact is less interior space. However, EV motors have been getting smaller over time, which means that by the time this car is ready, the negative impact of those four motors should largely be mitigated.
Wrapping Up: This Is A Great Move For BMW
The power, especially the torque of EVs, is incredible, and the ability to alter the output of electric motors thousands of times a second means you can put that power down. Still, if you can do this for every wheel instead of two or three of them, you should get even better traction and control. This means the quad motor BMW M-series car if released out of testing, could be the quickest car in its class and potentially like the E-Tron GT performance is for Audi, the quickest car BMW has ever made.
That would be a fantastic car worth owning, potentially ending my decades-long dislike of BMWs.
Rob Enderle is a technology analyst at Torque News who covers automotive technology and battery development. You can learn more about Rob on Wikipedia and follow his articles on Forbes, X, and LinkedIn.
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