Above is a chart which indicates many combinations of front and rear sprocket teeth count for the desired gear ratio.
Keep in mind that this chart excludes the effect of tire diameter changes.
In general, increasing the diameter of the rear tire and keeping the gear ratio the same will increase your ratio.
In other words, make your quad have more top end and less low end power. It will be slower to get up to speed but when its reached, it'll fly!
Keeping your tire diameter the same (as before), and decreasing the rear sprocket teeth count will also have the same effect.
It'll fly on top, but take longer to get there.
Reducing the teeth count on the front counter shaft sprocket will provide tons of low end power, but the motor will rev quickly.
Reducing the front sprocket teeth count is preferred by most hill climbers, assuming no increase in displacement was performed on their motors to get them to the top of the hill.
OK, use the chart to figure out which combination best fits your quad with the typical load (with your fat ass on it). The GOAL is to utilize all of the power band of the motor without bogging it down to quickly.
Thanks to www.pinnedoutracing.com