with bigger tires, it just sort of cancels out, unless you got the 4.636/5.429 x new tire diameter/stock tire diameter x 100 = % of speedometer variation.

I think.... I tried reversing it and it seems right this way...

32.7/29.5 = 1.051
4.636/5.429 = 0.854

1.051 (difference in tire size (increase in distance traveled per revolution)

0.854 (reduction of tire revolutions)

1.051 x .854 = 0.8974 reduction in tire revolution over stock gearing and tire size.

this is with 31 inch tires.

with 32.7 inch tires (about the biggest I have seen on an Xterra) it is .9466 or 94.66% of the original gearing. Not a huge difference. but a difference compared to the 110% that the 32.7" tires gives you.

This is making my brain hurt. you put the bigger tires on, and your speedometer slows down, but your crawl ratio goes up, meaning, you go farther for every revoution of the engine. With the gearing change, you effectively get to use bigger tires, and a 5%-11% reduction in gearing. 31" tires are a good thing in this instance. they allow you to crawl slower.