Gearing
As a rule just remember the following when making any changes to gear ratios:
Gearing a bike up to produce higher top speed with less acceleration is done using a larger front sprocket or a smaller rear sprocket.
Gearing a bike down giving it more acceleration with lower top speed is done using a smaller front sprocket or a larger rear sprocket.
Generally speaking changing one tooth on the front sprocket has a significantly larger effect on the gearing than changing one tooth on the rear sprocket. To make only a small change in gearing it is therefore necessary to change the rear sprocket size by one tooth, as changing the front sprocket makes a far larger difference in gearing.