I/ll give it a try.

A differential is basically a gearbox with different size meshing gears where the input shaft [ drive shaft ] has to
turn a certain number of revolutions in order to turn the output shaft [ axle/tire ] one rev.
Now, if the drive shaft has to turn, let's say, 3 and 1/4
turns to make the wheel turn 1 turn, we have a ratio factor of 3.25 to 1. This would be referered to as a 3.25 ratio differential.
From here you can see how tire size and different types of transmissions affect engine RPM's at given speeds.

The basics, anyway.