#1-You can pull off your diff cover and count the teeth on the ring and pinion gears,divide the ring gear count by the pinion gear count and carry 2 decimal points and you have your ratio.Example is 41 tooth ring gear divided by 10 tooth pinion = 4.1=4.10's.
#2-Axle ratio may also be determined by counting the wheel and drive shaft rotations -Select a level surface -Mark the tire edge (bottom) and a spot on the drive shaft so you can see it as it rotates -Roll the tire until the tire rotates exactly one rotation -Count drive line turns as the tire moves.
Example-Driveline turns 3 3/4 revolutions indicate your ratio is probably 3.73
4 revolutions 4:10
4 1/2 revolutions 4.56
5 1/3 revolutions 5.38

 

yea that sounds alot easier!

 

i have 38's on my truck and i have ordered 4.56 gears..i want more take off acceleration and power to also tow...
i have stock engine 318
just really opened up exhaust and gutted cat

will 4.56 be too big, and not allow much accleration?

 

4.56's should be fine.
In the Jeep world at least 4.88's would be the norm for 38's. Granted that unless you get back into the CJ's you're running 6 cyls or even 4's so you'll need more gearing. However, I would think that you'd want at the very least 4.10's and 4.56's would be better for 38's and the 318.

Here's a pretty good chart, you can use it to compare your stock specs to what it'd be with larger tires:


So, for example, if you had 31" tires approximately with 3.55 gears stock and then went to 38's with 4.56's you'd be staying about the same powerband wise and cruising RPM. Of course, that's before factoring in wind resistance and the extra weight of the tires.

 

lawlz

 

Somewhere I saw a way to approximate your gear ratio. It had something to do with your RPM's at a given speed and your tire size. I'll see if I can find it.

Heres what I was talking about: http://www.drivetraindirect.com/t_gear_calculator.htm

When you figure your tire size you need to actually measure the tire diameter, not just say 33 because your tires are 33's. It should give you a pretty good idea of what your current gearing is without tearing the whole rear-end apart.

 

i got 37s on my dodge and my 4.88s should be in on thursday and i got the 5.9 360

 

I think you'll be happier with the 4.10's. But, don't worry about it too much. If you find the "right" truck, buy it. When you're looking for a used truck, it's hard to get exactly every option you want.
I wanted a '98-'01 too, because I wanted a club cab with rear doors. When I found an unbelievably sweet '96 with 14K miles, I bought it. I love it. It has every feature I wanted except those rear doors. I don't really miss them.
Gears can be swapped, if you want to. Most folks swap to a lower (higher number) gear. Pay more attention to things that can't be changed easily, like body type, engine, trans, general condition, miles, etc.

 

Well - as it turns out, I did find a 2000 Sport Quad Cab 2500 back in January, and it's great - it's got the 5.9, with 4.10's, and it's a great rig! thanks for all the input!

YB

 

$.88s would be the best choice. 4:56 gears are what are used with 35s. I had 4:56s and 35s and wished I had 4:88s. But they werent available when I did my gears