The main functions which are performed by the transmission are :-

1. At low speeds, the torque produced by an IC engine is very small, which increases with increase of speed, peaks at some optimum speed and starts decreasing beyond that. This would mean that :-

(i) If the engine is directly connected to road wheels, it may not have enough tractive effort to start the vehicle from rest.

(ii) The practical considerations for the running of automobile under different conditions demands a large variation of torque at the road wheels, which would mean that it would not be possible to always run the engine at the optimum speed. Besides, the bigger engine would be required to cater to the torque requirement under most difficult conditions.

Thus, the main purpose of the transmission is to provide a means to vary the leverage or torque ratio between the engine and the road wheels as required.

2. The transmission also provides a neutral position so that the engine and the road wheels are disconnected even with the clutch in the engaged position.

3. A means to back the car by reversing the direction of rotation of the drive is also provided by the transmission.