Higher or lower gear ratio might be the deciding factor in how your scooter will perform. A higher ratio (shorter transmission) will make the engine reach maximum horsepower more quickly, meaning acceleration will be improved, sacrificing a bit of top speed. A lower gear ratio (longer transmission) has the opposite effect - higher top speed and slower acceleration.

This is the Malossi Secondary Transmission 15/47 (gear ratio = 3.13) Vespa ET4 / LX / S 2V / LX / S 4V 50cc with straight teeth for reducing friction and heat.

15/47 -> gear ratio: 3.13 = +17% for 2V / +25% for 4V