The stock gearing of your bike is likely to have been determined by choosing a compromise ratio based on what worked best for test riders in "average" conditions.
When we talk about gearing, we're referring to the final-drive ratio, which you get by dividing the number of teeth on the rear sprocket by the number of teeth on the front, or counter shaft (gearbox) sprocket. This figure represents the number of times the front sprocket has to rotate to turn the rear sprocket, and ultimately, it determines how engine rpm translates to road speed and how much torque there is at the rear wheel.
Setting up the gearing of any vehicle is a trade-off between acceleration and top speed.
Gearing a bike up to produce higher top speed with less acceleration is done using a larger counter shaft (gearbox) sprocket or a smaller rear sprocket.
Gearing a bike down giving it more acceleration with lower top speed is done using a smaller counter shaft (gearbox) sprocket or a larger rear sprocket.
(If you want better fuel consumption and net lower rpm, you’ll need to either add teeth to the front or subtract them from the rear)
A larger gear ratio (eg: 3.10) correlates to shorter gearing, while a low number( eg: 2.70) represents taller gearing.
All you really need to know is what your bike’s current gearing is (it’s printed right on the side of the sprockets) and then figure out how you’ll need to adjust the tooth count to change your bike’s performance.
It all goes back to how many times that front sprocket has to rotate to turn the rear sprocket and the wheel.