count each tooth as a percentage... the smaller the gear, the bigger the percentage. of you add a tooth to a 3 gear cog (i know, impossible, just an example)... you are adding 25% surface area. if you add a tooth to a 9 tooth sprocket, you are adding 10% surface area. say you are running 3-9... you would end up running a lower ratio if you added a tooth on front and rear cogs. kinda buzzed off martinis right now, so its hard to go in depth, but thats the basic concept i leard from my peewee motocross days.