Absolutely two in the back, because while accelerating load shifts from the front axle to the rear axle, so at the rear is where the traction is. In a Tesla Model S Performance Dual Motor, the larger motor is in the rear and the smaller motor is in the front.I'm currently working on designing an '82 Corvette high performance conversion, and have found the specs I want using 3 AMR racing 250-90 motors. This isn't ideal, because I would need to do a conversion on the front axis, but what is the general consensus on the best configuration for 3 motors of equal power in an electric car: is it 2 in the front and one in the back, as they have on some Tesla models, or would 2 in the back and 1 in the front be better because the motors are equal: unlike in the Tesla.
There is no existing Tesla model with three motors. If the proposed Tesla Model S Plaid variant has the dual motors at the front, then like existing cars with two motors at the front (so that different torque can be applied to each front wheel) the front motors will be much smaller than the rear motor. There are no real specs available for the Model S Plaid, but if the model is eventually built there will presumably be specs showing the motor power distribution. In the graphic in the Tesla website, it appears that switching between Dual Motor and Tri Motor (Plaid) changes between one and two motors at the rear (to the right in the image), not the front.