Wildfire Equipment Research & Development

Roscommon Equipment Center


Calculating the Load on a Fire Engine

This calculator was developed to estimate the total load on fire truck prior to fabrication. It requires the input of accurate information that you, the designer, must obtain. Your reward for doing your "homework" will be the reduction of costly design errors and the likelihood of a well balanced truck. You will need to enter accurate numbers into the calculator. The following discussion will help you determine the numbers to use.

If you have not read the REC booklet, Newsnote #3: Guidelines for Designing Wildland Fire Engines, please do so before calculating.  Newsnote #3 provides background information and definitions that will aid you in your fire engine design.

Vehicle Manufacturer’s Weight Ratings

If you are utilizing a bare truck chassis, the vehicle manufacturer or dealer can provide you with the chassis’ Gross Vehicle Weight Rating (GVWR) and each Gross Axle Weight Rating (GAWR) on the Incomplete Vehicle Document. This information is often found on a data plate on a door or door jam. Military vehicles will have this data on a dash plate.

Bare Chassis Weights and Wheelbase

This section asks for three items that are necessary for the calculations. Determine the bare truck weight by filling the truck full of fuel and taking the vehicle to a set of scales. Without occupants, weigh the vehicle to get a total weight and the weight on the rear axle. Also enter the wheelbase. You may refer to REC’s Weights of Common Components for calculating your load. Estimates include weights of water tanks, pumps, winches, and various other items.

Forward of the Front Axle

In this section, you must enter the weight of major items that will be placed on the vehicle during modification. Additionally, you must estimate the horizontal distance between the object’s Center of Gravity (CG) and the centerline of the front axle. The CG is the "balance point" of the object’s weight. In many cases the CG can be estimated as the center point of the object.  Refer to REC’s Center of Gravity Diagram for assistance.

Important: In this section of the calculator, only consider items that will be installed in front of the front axle.

Behind the Front Axle

In this section, you will enter weights of major objects that you place in the vehicle. Estimate the horizontal distance between the object’s CG and the center line of the front axle. Refer to REC’s Center of Gravity Diagram for assistance.

Important: In this section of the calculator, only consider items that will be installed behind the front axle.


After verifying that your entries are correct, click the "Calculate" button. The estimated weight of the completed truck and the weight on each axle will appear.  The results will also display the estimated percentage of the weight on each axle and the percentage of the payload on each axle.  A dialog box will give a general statement of what the results mean.  It might recommend that you make some changes.  Use "Reset" to start over.


Considerable effort has been made to make this calculator accurate and easy to use. The more accurate information you enter, the more accurate your estimate will be.  It is your responsibility to determine the accuracy of the results. Your final check for accuracy should be to weigh the completed vehicle with a full load of occupants, water, fuel, and equipment to verify that it does not exceed the manufacturer’s GVWR or GAWRs.

Tips & FAQs

Please refer to Tips & FAQs for more information about the calculator.

User's Pledge: I have read the instructions and understand that the calculator’s accuracy depends on my understanding of vehicle design principles and accurate input of the data requested. The interpretation of the results and decisions about their accuracy are my responsibility. By clicking the calculator link below, I accept this responsibility:

Detailed Calculator - Truck Chassis