One gear speed more can have various advantages: - better acceleration (figure 1), - more tractive power on hills (figure 1), - lower engine RPMs (figure 2), - Protection of the engine (figure 2), - lower noise development (figure 2), - lower consumption (figure 2).
These are two completely different approaches. In both cases the starting point is a four-speed transmission. We assume that this gearbox is combined with an engine with a nominal speed (RPMs at the maximum performance) of 5600 RPMs. The vehicle, in this case, should also be designed so that it reaches its maximum speed at these RPMs in fifth gear.
Now, in the left figure, the first - and the last gear are maintained and instead of two gears in between, there are now three. If the driver can change gear relatively quickly, the torque of the engine will be better applicable with this change. The maximum speed, and on level roads does not change much.
The right solution with a longer gear ratio in the highest gear helps a great deal here, now one can decide between using torque and performance, or for the protection of gears, engine and the saving of fuel by opting for a conservative driving manner.
There is another small advantage. Under favorable conditions, namely downhill highway driving without headwind, the maximum speed in the new fifth gear can be even higher than it was before. In general however, one must shift down into fourth gear to achieve the maximum speed. A different gear ratio simply cannot bring any more performance. 06/10