The scope of Vespa gearing is less broad than Lambrettas but still complicated. There are 2 things that can be changed to result in higher or lower than standard gearing. The primary drive consists of a smaller helical gear that is integral with the clutch assembly and a larger helical gear riveted to a cluster of 4 toothed gears.

These must be installed as a matched pair on small frames. Lastly the tire size can changed.

Below are calculators for the two main small frame Vespa gearbox options that will give gearing for a range of standard Vespa gearboxes without mixing separate gears from different models.

• The helical primary gear - "Primary Gear"
• The gearbox group (from a standard Vespa model) - "Gearbox Type"
• The tire size used - "Tire Size"

I have included some primary drives kits by Malossi and Polini. The resulting page will show gear ratios for each of the 3 or 4 gears and show an RPM to speed analysis at various engine revolutions.