Mechanical Stepped Transmissions
Torque conversion of mechanical transmissions is determined by the effective radii of the point of application of forces.
In case of mechanical stepped transmissions, a positively-engaged force or torque conversion normally takes place over gear wheels. The conversion characteristic hence depends on the gear ratio of the gears engaged together. As a result of the positively-engaged transmission, a conversion of the torque is only possible at definite levels. Each level represents a definite transmission ratio i which is the ratio of input speed to output speed

Eq. 3-23

Figure shows the conversion characteristic of a 4-speed transmission.
In this case four output maps emerge from the engine's delivery map. At the same time gaps remain between the transmission maps and the power hyperbola for P = const. which cannot be driven.
A stepped transmission should be designed in such a way that these transmission gaps have nearly no disturbing effect on driving. This can be achieved by increasing the number of gear levels or an appropriate choice of the individual ratios.