How does Tesla's transmission gear work?
There is no transmission, the motor is directly connected to the axle, although there is a differential box present.
That is what gives the Tesla amazing acceleration that blows away other higher-powered vehicles in the 1/4 mile or 0–60... there is no delay for shifting,,,just raw direct power.
The Model S has a single-speed transmission. There is no clutch or gear-shifting involved. Because of the wide power band of an electric motor, and its ability to produce torque at zero rpm, a simple fixed-ratio transmission is all that's needed. When you 'shift' into reverse, all that happens is the direction of rotation of the electric motor is reversed.
Early prototypes of the Roadster did use a 2-speed transmission. This has potential efficiency benefits (every motor has an optimum point for efficiency) but was deemed to be too complex for the gains and the simpler, more robust single speed gearbox was settled upon.
The basic version uses a single electric motor, located at the rear, to drive the rear wheels. All-wheel drive versions are available, which have a second motor which drives the front axle completely independently- there is no mechanical connection between the front and rear wheels. The front motor generates less power than the rear.