Originally Posted by Large
What exactly is your advice ??
My advice for anyone wanting or wondering to regear is to determine first the size of tire desired, then the top speed that the truck needs to comfortably cruise, then the desired engine rpm of the actual engine in use, AT that hwy top speed.
THEN, find out what the top gear ratio is of YOUR transmission and with this data you will determine the axle ratio that will give you THAT rpm at THAT speed.
This is for a mixed use truck. If it's a crawler that don't care about hwy then adjust this data to fit your needs, but really this is the only way to determine your needed ratio. It has everything to do with how your engine likes to sing at that hwy speed. A V8 will lumber along the hwy at 1300 rpm all day, my 4 cyl prefers to be at more like 2600 rpm at that speed. So, even with the same transmission you can see that I will still want a drastically different ratio on the rear end. And the same is true of two trucks with the SAME engine and tires, but running different transmissions. They will also want different axle ratio.
So, since you know what engine you have, and what tire you want, all you need to find out is what your 6th gear output ratio is, and ask yourself what your hwy cruise speed will be. Then go to grimmjeeper's page to calculate the diff ratio.