Secondary gears -MALOSSI- Piaggio 50cc (1998-)- 14/47 = 1:3.36

Extending the gear ratio is useful if the engine performance has been increased by successful tuning measures. With the extended gear ratio you can convert your extra power into more speed.
In addition, the cylinder and the rest of the engine are spared, because they don't have to be revved up as much.
In series engines a longer gear ratio is usually not useful, because in most cases the power is not sufficient to convert the extra gear ratio into top speed.
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