Gear Ratio Calculator

This form allows you to calculate final drive ratios as well as see a comparison of speeds and RPMs within operating ranges of the vehicle. This calculator is useful for planning your rig, allowing you to see what kind of performance to expect from different combinations.

Disclaimer: This form is only to be used for estimation purposes. Exact results of combining equipment may vary from the estimates provided in this form. The data provided here is done so as-is with no warranty expressed or implied.

Note: This calculator is continually being updated. The lists of available equipment will probably never be complete. If you find that the parts you would like to use are not yet listed, please send the information to me and I will do my best to include it as quickly as possible. It has come to my attention that my grimmjeeper.com email address doesn't always forward mails to my real address. So here's one that hopefully works a little better: grimmjeeper@gmail.com

Detailed Instructions Here

If you're going to regear your 4x4 it's a good idea to consider adding a locker or limited slip differential at the same time. If you're having trouble figuring out which one is for you, I've written an introdution to differentials and lockers to help you decide.

If you are wondering what all of this gearing talk is all about, I've written up an introduction that walks you through The basics of gears and why you would want to change them.

BETA: Calculate your new mechanical speedometer gear here

There are two copies of the form so that you can do a side-by-side comparison of two combinations.

Step 1: Select transmission from the drop down list or, if it's not in the list and you know the gear ratios of your transmission, enter them below.

Number of forward gears
1st Gear
2nd Gear
3rd Gear
4th Gear
5th Gear
6th Gear
7th Gear
8th Gear
9th Gear
10th Gear
Reverse
Manual or Auto with lockup torque converter
Automatic without lockup toque converter

Step 2: Select transfer case from the drop down list or, if it's not in the list and you know the gear ratios of your transfer case, enter them below.

High Range
Low Range
STaK 3rd Range

Step 3: Select underdrive.

High Range
Low Range

Step 4: Select axle gear ratio.

Ratio

Step 5: Select tire size.

Inch
Metric /R

The following chart lists the final drive ratio of all combined gears (transmission, transfer case, underdrive, axle) in all possible combinations

Final Drive Ratio
Gear	Underdrive High Range			Underdrive Low Range
Gear	Transfer Case High Range	Transfer Case Low Range	Transfer Case STaK Range	Transfer Case High Range	Transfer Case Low Range	Transfer Case STaK Range
1
2
3
4
5
6
7
8
9
10
R

The following chart lists the crawl speed you will be going while the engine is at a given RPM. Crawl speed is calculated based on the lowest low range (transfer case and underdrive in low range) available in your rig.

Crawl Speed at Given RPM in Feet Per Minute
Gear	RPM	RPM	RPM
1
2
3
4
5
6
7
8
9
10
R

The following chart lists the road speed you will be going while the engine is at a given RPM. Road speed is calculated based on the transfer case and underdrive being in high range.

Road Speed at Given RPM in Miles Per Hour
Gear	RPM	RPM	RPM
1
2
3
4
5
6
7
8
9
10
R

The following chart lists the RPMs your engine will be turning while driving at a given speed in MPH.

Road RPMs at Given Speed
Gear	MPH	MPH	MPH
1
2
3
4
5
6
7
8
9
10
R