hey i was just lurking about and saw no one has responded to you. what a shame. i have seen some post using all types of technical talk and nothin here . well i am no smart guy but i think (and i'll bet some one will correct me) it can be explained simply, like if you look at the circumfrence (tooth count is used) of your gears. think about two gears meshing (not much difference for this example) a little one driving a big one, little one might do several rpm before big one does even one rpm. changing the ratio (tooth count)of one (or both)gear(s) can give you more max speed but strain the motor
or it can lower the maxspeed and let you climb a wall. that probably confused you more but hey i tried
on my bike stock gears i think are 15/45, 15 being the drive front gear and 45 being the rear. i changed the front to a 16 so with that you could sort of say i gained 1 more chain link per revolution meaning the rear wheel is moving 1 link faster (sorta of) making the bike go faster at the same rpm. or you could look at it as i can slow down rpm's to maintain same speed as before. i am looking at lowering the tooth count in the rear which is like raising the tooth count in the front. ok i give up now
by the way tire size has to be looked at too to understand more in depth the "big picture"