common knowledge, by going smaller you are changing the rear ratio to a lower gear when going taller you are raising it to a taller gear.

when i had my 69 coronet i was running a 3.91 sure grip but with a 29.1" tall street
my final drive was approximately 3.45 and allowed me to take the car on the highway
and run at 70 with out over revving the engine.
at the track i would swap out to a 26" tall drag radial which was the factory tire size
giving me back my out of the hole grunt