Rear ratios explained

Very generic here as transmission ratios, motor torque and tire size have alot to do with this as well...generally the higher the numerical ratio the more torque will be applied to the wheels.
So :
3.77 = higher ratio = more torque, less speed
3.31 = mid ratio = bit less torque than 3.77 but a bit more speed
3.08 = lower ratio = bit less torque again over 3.31, alot less that 3.77 but more speed than both others

Ideally you have to look at what you plan for loads, average road speeds, hill sizes etc and purchase the best for that type of driving.....here in Canada they govern road speeds to approx 100km or 62.5mph and mountains at one end of the country verses flat through the middle to rolling hills......not much point running a low ratio [like 3.08 as you would suffer on the hills and there is no place to run 80mph/130km]. So get everything right and you will be rewarded with great MPG, get it wrong and you will hate your truck big time.

Keep in mind this is a very none engineered response ....if you want that i can provide it as well....lol.

 

It really depends what kind of work you're doing and what part of the country you're traveling through.

A lot of this equation is how much torque your engine has in a given truck. If you are geared High, which is numerically low, like say a 3.08 rear, it takes an engine with more torque to be able to turn that versus turning rears that are say 3.77 or 3.9.

Basically lower numerical number gives you a higher gearing, which gives you a higher top speed, gives you a lower cruising RPM at 65 or 70 or whatever, but also is not going to give you as much power in the Hills. And the opposite is true.

One thing I've always been curious about is backing up or pulling out on a steep hill when you have a 2.63 gear ratio.

Unless the truck has a super deep low gear and reverse gear that's got to be tough.

 

High reverse would even be useless on flat ground for sure. My guess is you wouldn't be able to let out the clutch.
Certainly with all the stunts performed nowadays someone has tried to go up a grade backwards

 

I wonder about pulling out even on a reasonable grade or backing into a dock.

I have 390 Rears and I can let my clutch fully out and back into a dock.

It's just a guess but with 263 rears you've got to be doing like 10 or 15 mile an hour! Not really but I can't see how you could let your clutch fully out you must be moving at a pretty quick rate of speed.

I'm sure someone can answer it but it can't be easy to pull out on an uphill grade when you have that kind of gearing.

 

Juat a little fun with the gearing caliculator.

 

3.90 is good. My Fl 60 has them with a spicer 6 speed and it works well. My ‘72 with 3.55’s is a little too fast when light. Have to slip the clutch. My ‘67 with 4.11’s is just right and comfortable to maneuver even without power steering. The ‘51 in reverse under is a slooooow creeper
High rears is why I think that so many auto trucks nowadays get that uncontrollable jumpyness when backing up.with manual can slip the clutch a little with anything higher than 3.90’s to keep it rolling smooth and steady controlled by your left leg and the pedal. Bad for clutch but easier on the truck and your mental stress.