you can also jack the rear up, count the number of times the tire spins to one pinion rotation, that will give you a ball park. 6 cyl ax 15 yj's had 3.07:1 but there were a few with 3.54:1
so if the tire spins 3 revolutions, 307's spinds 3 1/2 times 354's
thats not backwards is it.. crap brain hurts..