4. Conclusion

A vehicle with an internal combustion engine needs a transmission to adapt the available engine power to the power demand at the axle.

The power required by the axle depends on the driving conditions encountered. These vary, which is why a gearbox needs to have several ratios.

This article sets out the basis on which gear ratios can be objectively determined at first glance. In fact, other constraints, which are not driveability or traction constraints, can influence or modify the basic gear ratios, the number of ratios, or even the type of transmission chosen.

We're thinking in particular of environmental and energy constraints (pollutant emissions, CO ₂ ) on which the transmission plays a role, through its own efficiency or the engine's operating point.

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