Dual Motors - Different Rear and Front Motors?

[JSWE]

I was just looking over my invoice, and I noticed that the rear motor is described as a three phase, six pole, internal permanent magnet motor and the front motor is described as a three phase, four pole, induction motor. Can someone simplify this description for me and explain why the two motors aren't the same?

 

[MP3Mike]

The difference is that the induction motor can be put to sleep when not need for efficiency purposes. the PM, permanent magnet, motors have to have power applied to them any time they are turning, so while they are more efficient when making the car move, they are less efficient if they aren't needed.

Normally Tesla has the gearing slightly different between front and rear so one is more efficient at cruising while the other has more power for take-offs.

 

[chillaban]

Additionally having two motors of different designs is supposed to improve reliability since it means the same design defect is unlikely to affect both.
From an engineering standpoint promoting some internal competition between two top runner designs results on a stronger product too.