Divide the number of teeth on your rear sprocket with the number of teeth on your front to get your ratio.

The lower the ratio, the better your top speed but it reduces your acceleration. The higher the ratio, vice versa.

So the trick is, to get better top speed you must increase the size of your rear sprocket by 1-2 teeth.

Or if you want a more dramatic difference, the math says decrease the front sprocket size by 1 tooth. You'll be able to cruise at higher speeds at lower RPM at the expense of acceleration.

Beware that in the end, the final result is always influenced by how much power the engine makes in the first place. So if ur engine is small, don't expect miracles.

Try out small changes in ratio first until u get a feel for where you are in relation to the performance you want.

My TNT600 would rev past the redline, indicating it was under-geared from the factory. When my chain wore out, I increased the gearing by lowering the sprocket ratio. Now it does 150km/h at just 7000rpm, which is better for my highway commute.

Good luck.