If I recall right......
both wheels off the ground, spin one wheel, count rev's of yoke....
if both wheels spin in opposite directions X2 your count (open),
if only one wheel is spinning use that (open),
if both wheels turn same direction
use that number (suregrip).
helps to mark both the tire and yoke....

3 and 1/4 turns will be around a 3.23
2 and 3/4 turns will be around a 2.76

So with both wheels turning opposite a 1 and 1/2 spin
will be a 3.00 something, 1 and 5/8 turn will be close
to a 3.23, ect.......

course you can always look for that tag on the rear
cover, but there often missing and sometimes even wrong
if the rear has been opened......
or pull the rear cover (8.25, 9.25 rears)and look for the stamp on the
ring gear