That really depends on what gear set your truck has in the differential and what diamter rear tires you are running.

Use this chart:

http://www.sierrabronco.com/TireGearRatio.htm

and the following:

Pulling the rear differential cover (& counting the teeth) is the most accurate method to determine gear ratio but another way to check the rear end ratio is to jack up one tire if you have an open diff, or both tires if you have a working posi or locking differential. Rotate the tire one full revolution for posis and lockers -or- 2 full revolutions for open diffs. Carefully count the number of full revolutions the driveshaft makes. This is your gear ratio. In other words, if the drive shaft turns 3 ¾ turns, you probably have a 3.73 gear ratio. Turning the tire for twice the number of full revolutions and dividing the drive shaft revolutions by two will give you a more accurate reading.


Last edited by Hot Rod John; 08/08/2011 12:44 PM.
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