Could somebody explain gearing in the rear end for me. I'm lost when poeple keep saying 4.11 and 3.08 rear ends. How do I know what my truck has in it?

 

If someone has 4.11 gears, that means that your driveshaft has to turn 4.11 times per one revolution of your tire. AFAIK, almost all broncos came from the factory with 3.55 gears. If you post your vin, Im pretty sure we can tell for certain.


Rich

 

So what is a good ratio to have depending on tire size and engine power?

 

What size tires are you running? What do you do with your bronco? All highway miles? Tow? Personally, I like to have a low end grunt more than a highway runner. Plus, selecting the proper gearing can make your around town mpg possibly increase because your motor will not have to search to find the correct rpm by up and downshifting.


Rich

 

rpm = mph x gear ratio x 336 / tire diameter

This is the formula for calculating gear ratios based on tire size. The idea with this formula is to keep the engine spinning at or near its power band...(most productive rpm range). If you have a transmission with an overdrive gear, you can factor in the overdrive ratio as well...

rpm = mpg x gear ratio x overdrive ratio x 336 / tire diameter

By way of example:
2349 = 65 x 3.55 x 336 / 33 <----not so bad!

2720 = 65 x 4.11 x 336 / 33 <----gettin' a little wound up!

1762 = 65 x 3.55 x .75 x 336 / 33 <----ouch! low! (trust me this is where I am right now)

2040 = 65 x 4.11 x .75 x 336 / 33 <----now thats better!

This is where having overdrive can be helpful because you can gear up without sacrificing as much power and MPG. With the OD setup you could even go up again and still be under the rpm you'd be turning without the OD.

 

http://www.4lo.com/4LoCalc.htm

 

The ratio is not encoded in the VIN - only on the axle tag and the AXLE code on the door sticker.