Gear kits are typically used when trying to gain more top speed.
As gearing ratio’s are usually well set from the factory, in almost all cases the installation of a gear ‘up’ kit (lowering the ratio for more top speed) should not be used in an otherwise standard scooter. The beneficial use of gearing up a scooter is on a motor which has been modified to produce more power (performance exhaust, cylinder, carb, ect). In almost all cases, a lower gearing ratio is what a scooter tuner would aim for, to achieve more top speed and give the motor more gearing to appropriately match the higher power output.
Within a scooter diff gear there are 2 sets of gears, the primary and secondary drives. Both are made up of 2 gears each. The Primary drive is made up of the Primary Drive Shaft (shaft that the clutch and rear torque pulley sit on inside the CVT transmission) and the outer gear of the idle gear. The secondary drive is made up of the pressed shaft gear inside the outer gear of the idle gear and the final drive gear which is pressed onto the drive shaft (which the rear wheel bolts to).
Working out the amount of difference is done by calculating how many rotations of the primary drive shaft (CVT side of the diff) equate to one rotation of the drive shaft (and therefore the rear wheel). An average 50cc scooter will have somewhere between 11 – 13 rotations of the primary shaft to the drive shaft as a very generalised rule.
for instance, if the standard gears are:
Primary – 13 / 46 Secondary 15 / 48
To work out the gearing ratio: Primary large gear ÷ small gear, secondary large gear ÷ small gear. Then multiply both results for the overall ratio of number of Primary shaft rotations to every single wheel rotation. In this instance with the gear ratios listed above the result is 11.2/1. When working out the difference with the installation of a gear up kit, simply substitute the gearing ratio of the gear kit to plan to install (whether primary or secondary) and see what the difference is compared to the standard.
It is important to note that not all Malossi gear kits will lower the gearing ratio! Please use the information above to make an informed decision.