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

If you have not read the REC booklet, Guidelines for Designing Wildland Fire Engines, please do so before calculating. An on-line version is available by clicking here. Guidelines provides background information and definitions that will aid the user.

If you are utilizing a bare truck chassis, the vehicle manufacturer will give you the Gross Vehicle Weight Rating (GVWR) and each Gross Axle Weight Rating (GAWR) on the Incomplete Vehicle Document. If you do not have an Incomplete Vehicle Document, check the door area for a data plate that lists this information. Military vehicles will have this data on a dash plate.

This section asks for three items necessary to do the calculations. To determine the bare truck weight, remove any chassis item that will not be on the complete vehicle. Example: If you will not use the truck’s original bumper, remove it. If you have a military vehicle and will not use the payload bed, remove it. Take the vehicle to some scales. Weigh the vehicle to get a total weight and the weight on the rear axle. Also enter the wheelbase. If you are using a vehicle with a tandem rear axle click here for a illustrated definition of the wheelbase. A list of common component weights is available. Estimates include weights of water tanks, pumps, winches and various other items.

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. Click here to see a diagram that helps describe how this can be done.

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

In this section, you will continue to enter weights of major objects that you place in the vehicle. Again, estimate the horizontal distance between the object’s CG and the center line of the front axle. Click here to see a diagram that helps describe this.

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

After checking 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 better the information you enter, the better your estimate. However, it is your responsibility to determine the accuracy of the results. Your final check for accuracy should be to weigh the completed vehicle with water, all equipment and occupants to see that it does not exceed the manufacturer’s GVWR or GAWRs.

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 asked. The interpretation of the results and decisions about their accuracy are my responsibility. I am willing to take this responsibility and use the "Wildland Fire Engine Weight Calculator".