Included with this extensive documentation is a dynamic spreadsheet that can be used to determine your COG and Roll-Over angles.  Please read the documentation below to understand how the spreadsheet does it's job.  You can download it HERE.

Feel free to use the Table Of Contents below, or simply scroll down to view the entire document.

Table of Contents. 2

Introduction.. 4

Capturing Weights and Measures. 5

Tools Needed. 5

Measured Values. 5

Calculated Values. 6

Jeep Setup. 7

Off-Scale Measurements. 8

Length of Wheelbase - LWB. 8

Width of Wheel Track Base - LTB. 9

Front Axle Height – HF1. 9

Weighing Your Jeep. 11

Front Axle Weight - WF.. 11

Rear Axle Weight – WR1. 12

Rear Axle Weight Modified – WR2. 12

Front Axle Elevated – HF2. 13

Passenger Side Weight – WP.. 13

Calculating the Centers of Gravity.. 14

“X” The Wheelbase Center of Gravity (WBCG) 14

“Y” The Wheel Track Center of Gravity (WTCG) 15

“Z” The Center of Gravity Height (HTCG) 16

Roll Over Angles. 18

The CG “Balancing Point”. 18

Anatomy of a Roll Over.. 20

Calculating Roll Over Angles. 24

Side Roll Over Angle - WARNING!!! 26

Driver Side Roll Over Angle “DSROA”. 28

Passenger Side Roll Over Angle “PSROA”. 29

Rearward Roll Over Angle “RWROA”. 30

Forward Roll Over Angle “FWROA”. 31

Summary of Roll Over Angles. 32

Tuning your Jeep’s Roll Over Angles. 34

Gravity Support Structure. 34

Lengthen the Wheel Base or Widen the Wheel Track. 34

Weight Tuning.. 34

Redistribute Physical Weight 35

Lower the Physical Location of Weight 35

Remove Unneeded Weight 36

Apply or Remove Cantilevered Weight 36

ROA Alarm System... 39

Wilson Instruments. 39

C of G / ROA Spreadsheet.. 41

Worksheets. 44

Measured Values. 44

Calculated Values. 44

Roll Over Angles. 45

Addendum: Second Edition.. 47

Force and its effects on our Jeeps. 47

What is a force?. 47

Describing Force. 48

Why all the emphasis on this?. 51

Force Descriptions. 51

Introduction

So often in our trail side conversations we talk about the CG (Center of Gravity) of one Jeep being higher or lower than the CG of another Jeep, and we relate this not only to the ability to get up or down a slope, but also to the dreaded thought of rolling over.

Yet most of us have never really figured out where the Center of Gravity is actually located on our own Jeep and similarly what the Rollover Angles are.

Why haven’t we done this?  Well to be honest, probably because it isn’t so easy to do.

This write-up is an effort to provide a process that most folks can follow to determine, with a reasonable degree of accuracy, the Center of Gravity and Rollover Angles for their own Jeep.

There is some mathematics involved here, Algebra, Geometry and Trigonometry.

However, if you are like me and not a math wiz kid, don’t let that scare you away.  I have automated all the math via an Excel spreadsheet. 

All that is really required is that you follow some simple directions, take some accurate weight and distance measurements, and then just plug the numbers into the spreadsheet.

If you hang in here with me and follow this process through you will be rewarded with the locations of the following values for your Jeep.

If you can use a tape measure, get a few minutes access to a truck “weighing scale” and you can type some numbers into a spreadsheet you can do this.

Capturing Weights and Measures

In this section you will take some specific measurements of your Jeep following these three process steps.

*       Preparing your Jeep for off-road use

*       Measuring lengths and heights in your driveway

*       Measuring weights at a truck stop scale

Tools Needed

You will need the following tools.

*       Tape Measure

*       Access to a truck weighing scale for approximately 5 minutes

*       A means to elevate the front tires of your Jeep at least 24 inches off the ground (Ramps, blocks, a trailer with car ramps on it, etc.)

*       A Helper

Measured Values

During this process you will measure and record the values shown in the table below.  Each will be explained in detail within this document.

Please note I have put fictitious numbers in this table to use in the examples throughout this document.  You will need to record your own Jeep’s data in this table for use in the formulas and spreadsheet.  I have provided a blank table at the end of this document for you to use for this.

Convert any fractions to decimal values.  For example, a wheelbase measurement of 92 and 5/16-inchs would be converted to 92.3125 inches.  LWB = 92.3125

Here is a table to assist you in converting fractions to decimal format.

Fractions to Decimal Conversion Chart

Calculated Values

Using the data values you recorded above, the following values will be calculated and used in your efforts to determine the Center of Gravity and Rollover angles.

If you would like, you can calculate these values yourself.  I have provided a blank table for you to record these values in at the end of this document.  However the Excel spreadsheet will perform this for you automagically!

Jeep Setup

Before you begin to make any measurements you will need to set your Jeep up just as if you were ready to take it off road.  This setup vital to accurately determine the Off-Road Center of Gravity and Roll Over Angles of your Jeep.

Please do not skip this step.

Whatever you do to prepare your Jeep for an off road trip, do the same now. 

Pack that toolbox, spare parts, Hi-Lift Jack and anything else that you would normally bring.  Make sure everything is safely anchored down.

If you have two sets of tires, one for the street and another set for off road, put the off road tires on and air them down to the level you would use off road.

Fill your gas tank.

If you would normally off road with someone in the passenger seat, or any other seats for that matter, make sure this folks are available to keep these seats warm when you are taking the weight measurements.

I cannot overemphasize the importance of weight and weight distribution in and on your Jeep to accurately determine the Center of Gravity.  Your efforts in setting your Jeep up now will be rewarded in accuracy later.

Off-Scale Measurements

These measurements should be taken away from the weight scale so the scale is not tied up when it isn’t necessary.

With a friend, measure and record the following values.

Length of Wheelbase - LWB

Measure your Jeep’s wheelbase length while it is sitting on level ground and fully prepared for an off road trip.

Your Jeep’s wheelbase is the distance between the centers of the front tire footprint on the ground and the rear tire footprint on the ground.  This is a bit difficult to measure accurately, however we can get it by measuring the distance between the axle hubs.

With a friend, measure the distance between the center of the front axle hub and the center of the rear axle hub.  This will be equal to the length of your Jeep’s wheelbase.

Make all measurements accurate to a 1/16 of an inch.

Here is a drawing of what you will need to measure to capture the wheelbase length.

Remember to convert fractions to decimal values. 

Width of Wheel Track Base - LTB

Measure the distance between the outer edges of your rear tires.  This is the Track Width of your Jeep.  Convert any fractions to decimal values and record this measurement in inches as LTB.

Here is a drawing of the measurement you need to take.

Front Axle Height – HF1

Measure the distance from the center of your front hub to the ground and record this as HF1.

Be sure your Jeep is sitting on level ground when you do this.

Weighing Your Jeep

Drive your Jeep over to the local friendly neighborhood weigh station. 

Be sure to bring whatever means you will use to elevate the front axle with you, and remember to take whatever this is out of your Jeep before you weigh your Jeep.

Also remember to put those other warm bodies in their seats before you take any weight measurement.  This includes you too!

Potential Scale Locations

*       Major Truck Stops

*       Highway Roadside Weigh Stations

*       Agricultural Centers (Bulk Grain Sales)

*       Salvage Yards