[NHRABill]

Figuring your gear ratio is easy.

Jack the complete rear axle off the ground

Mark a tire with a line

Mark the drive shaft with a line

have one person turn the tire a complete revolution

while the other person counts how many times the drive shaft turns.
for example if you follow the above instructions and your 1 tire revolution may = 4.10 turns on the drive shaft and there is your answer.

a 3.73 rear gear is a nice truck gear for people that haul with a 3 speed trans. Swapping the rear gear is not difficult at least the ones that I have done.

The ford 9" is by far the easiest of all rear gear swaps but I am sure you have the big boy rear on those heavy duty trucks. I have swapped many ring and pinion gears on GM cars 10 bolt 12 bolt cars as well as corvette centers. from the 2.73 to a 5.13 gear it is a CHEAP and easy mod to do yourself or get done for you. Changing the rear gear means a WORLD of difference in engine RPMs do your math tons of online calculators out there check out Hot rod sites for one If you have a truck with decent power and torque you should have no problem if you are an average driver with a weekly load in a non mountain area