I mean: electric motors can rotate at very high speeds. Do it even need a gearset? Or can it just rotate from 0 RPM to say, 15k RPM? Or there is a torque curve or efficiency issues involved?
AC motors (like the ones Tesla use), work by pushing a sinusoidal wave around the "outside" of the stator, while a similar sinusoidal wave (at a retarded phase) is run inside the stator. This creates a magnetic field which is "ahead" of the stator's field (well in forward mode) which "pulls" it toward the field. The torque curve is "constant" and the speed is limited only by how well you can modulate that voltage. (and of course the mechanical construction)
Source: http://www.teslamotors.com/support/model-s-specifications