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So they added the Switched Reluctance Motor technology used in the Model 3 for the front motor, improving efficiency.

It's a permanent magnet motor. It's an IPM design so some amount of the torque comes from reluctance, but the majority of the efficiency is from the permanent magnets providing the field rather than having to burn energy through the induction motor's copper bars to provide it.

Which is interesting. I wonder what the math looks like, since induction motors (without the heavy magnets) tend to be lighter. I can see why they'd avoid a rotor-coiled motor, since that comes with lifetime constraints.

As I understand it, the permanent magnet motor is more efficient at low fractions of maximum torque/power output. So, when cruising, the rear motor will be powered down. When accelerating heavily, the rear motor can kick in.

Induction motors are worse at regeneration at low speeds, but as poster below said, their advantage is that they can be powered down and not impede coasting.

I think they hope to be able to match power requirements of highway cruising using a PM motor, so they don't take losses spinning AC motor way below its power rating.

Will it deteriorate?

With adequate cooling, permanent magnet motors can last a decade or more, even in the most demanding applications

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