[George16]

You can change the ratio by changing the pinion and/or ring gear.

Issues, only if the spiral cut ones were not cut at the same angle.

Both ring gear and pinion determines the pitch.

Either pinion or ring gear gear setermines the gear ratio.

For example:
43/10 = 4.3:1
42/10 = 4.2:1
43/11 = 3.9:1
43/13 = 3.3:1

Anytime you change the number of teeth on either pinion or ring gear, the ratio changes correspondingly.