The easiest and cheapest way to affect the ratio's is quite simply your rear tyre, 4.00x10 will raise the overall ratios, 300x10 will lower them. (The use of a 4.00x10 tyre will need the bump stop of the engine casing grinding off!)

A more efficient and controlable way to adjust the way your gearbox works by lowering or raising the ratios by means of fitting different front or rear sprockets.

Front sprockets.
These raise the gearing the more number of teeth it has, and it quite a high percentage. Sizes available are :-
14T** 15, 16, 17, 18, 19, 20, 21.

Rear sprockets
These lower the gearing the more number of teeth it has, but in lower percentage then the front. :-
44, 45, 46, 47, 48, 49, 50.

By choosing different geaboxes and or the large number of variation on sprockets, you can alter your ratios to suit you and the conditions you use your scooter, as well as power made. It does'nt always equate that bolting on a performance kits will need the raito to be raised to gain more speed. In fact the opposite can be found in sme cases, in that lowering your gearing will give you more top speed in certan curcumstances. For example a scooter with a bolt on kit and expansions made to rev harder, may well require lower gearing in order to rev out in top gear. The extra speed will come from the engine revving harder. If the gearing is to tall, the scooter may well not rev as hard, thus a lower top speed is seen. On scooters with a lower revving kit / exhaust combination, higher gearing can be used as the scooter will make its power lower down, and probably will not be cable of "reving out" to to the restriction of how it works. In this case the higher top speed is gained by the torque of the set up.

** (we would recommend having a 14T machined with the front collet other wise the sprocket can spin round.)

The trouble with fitting different sprockets is then finding a chain that will fit the combination used can be tricky. Where we have quoted a stretched chain, this is a worn chain that normally would be to large to use on standard set ups due to it being to long for tensioner adjustment. Geniune Innocenti chains are actually very good quality, so as long as all links look secure, all rollers have no damage, it is more then likely quite safe to use. Beware of new pattern chains on the market, some are not very good quality at all, ask your supplier for more details.

All gearboxes between series three Lambretta machines are interchangeable, they should really be changed as complete units though, even in most cases down to the endplate that holds them in place. You cannot unfortunately change one gear at a time (except in some rare cases), i.e. if you want a higher forth gear you cannot just take that from a different set up to gain more speed. Even though many gears may share the same number of teeth, they (again rarely) are not interchangeable one at a time, for example a GT 2nd gear has the same amount of teeth as the SX150 3rd gear, but the actual gears are not the same.

In the tables below you will find listed gearboxes as per each machine, these are as would have been fitted to the scooter leaving the Innocenti factory. Many racers and tuners swap gearboxes with modified machines to gain the best from their set ups, and it is fair to say unless you have modified you machine is some big way, you will gain nothing from changing the gearbox to a different type. There are some exceptions to this last statement, but it all depends on your individual machine.

For you to want to change the ratio, you would have had to have some sort of conversion to your machine, i.e. not just a new carb, racy exhaust and a bit of a tune. Capacity changes (i.e. 125 to 150cc) Imola and TS1 conversions (amongst the two more popular ones) and the fitting of a side car would probably be the main reasons for changing gearboxes. Even then it is not absolutely necessary to change the whole gearbox itself, many different overall ratios can be affected by simply changing the front or rear sprockets, again it depends on your machine and the reason for the need to change.

OK in the explanations below you will see the primary drive listed, this is your front and rear sprocket, the smaller the front the larger number the rear. The four (in most case) gears and ratios are then inside tables, the group teeth is some times refereed to as the cluster or Xmas tree.