A car's transmission typically serves two purposes - to change the gearing of the car and to allow the left and right wheels to move at different speeds, which is necessary for maximum grip in the corners (read about differentials.)
Because electric motors spin VERY fast, a transmission typically is necessary to reduce the gearing of the car, so that the wheels rotate fewer times than the motor, making the car drivable.
Most cars do not have many options in terms of types of transmissions, however, 2WD off-road cars do have some - they allow you to change the number of gears in the transmissions and the layout of their transmission.
The number of gears imn a transmission may vary. Sometimes this will change the weight distribution of the car, or it can also allow you to run the motor with reverse rotation, which will change the car’s weight distribution on acceleration and braking.
Mostly applicable to 2WD 1/10 scale off-road cars:
Stand-up transmission case
- More rear traction
- Moves weight to rear of the car
- Generally suited for low-grip conditions
Laydown transmission case
- More on-power steering
- Moves weight forward
- Generally suited for high-grip conditions