The scope of Lambretta gearing is very broad. There are 3 things that can be changed to result in higher or lower than standard gearing. The primary drive consists of a smaller sprocket which attaches to the end of the crank and a larger sprocket which also acts as a basket for the clutch. A duplex chain links the two. The gearbox itself is made up of 4 free gears on an output shaft and a matched 1 piece cluster of 4 toothed gears. These must be installed as a matched pair except in some cases where a free gear with one less tooth can be added to the output shaft and still mate with the cast gear cluster. Lastly the tire size can be adjusted with slight modification to fit a nonstandard 4.00x10 tire.

Below is a calculator that will give gearing for a range of standard Lambretta gearboxes without mixing separate gears from different models. These are currently only for bikes after the LDs and not including the J range. The following choices will have to be made:

• The primary smaller toothed gear at the crank - "Crank Sprocket"
• The clutch bell toothed housing - "Clutch Bell Sprocket"
• The gearbox group (from a standard Lambretta model) - "Gearbox Type"
• The tire size used - "Tire Size"

Be aware that the chain length will have to be modified if not using a standard (shown by the letter 'S') Lambretta primary drive combinations. The resulting page will show gear ratios for each of the 4 gears and show an RPM to speed analysis at various engine revolutions.