Gearbox calculations simplified
To calculate the gearbox final drive gear ratio you
divide loose gear teeth by cluster teeth.
To calculate the gearbox primary gear ratio (the sprockets) you divide the
clutch sprocket by the front sprocket.
To calculate the overall ratio you multiply the two together
To calculate the percentage drop from gear to gear you get the ratio of
the gear you are in (IN) and the gear you are changing to (TO). The
formula is ((TO-IN)/IN)*100.
Subtract IN from TO then divide it by IN, then multiply it by 100. This
will give a negative percent i.e. pacemaker is 19.65% (good), nice. SX 150
is 29%, (not good)
Developments gearbox information
Lambretta gearing calculator
Finding Neutral Hint: Position the selector arm
to point to the "X" of the SX engine number or the "I" on the LI casing.