gear ratio

If buying used...the previous owner(s) might have changed the diff gear set. This is from an old thread on HOW2 without lifting the vehicle


2500 Suburban - How to determine ratio?

Best to then tie/tape a length of string on the drive shaft. Note a
datum.

Then roll the vehicle one tire rev using the valve stem as a datum

Count the full turns and the fraction left. That is the diff ratio
and makes no matter what size tire or suspension lift, etc.

Remove the string.