Budman what gear did you have and what did you replace it with? And what tire and ring and pinion did you have versus what you put in?

 

Mine has 235/70/16 tires.
Had a 3:55 with a 21 tooth.
Went to a 3:08 with an 18 tooth.

I am sure if you doodle a bit you might be able to figure your out.
I am thinking I had a 15% change in ratios so if you figure yours there you go.
Or use the 3mph per tooth.
Smaller driven gear increases the spedo reading, larger slows it.