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Determining Truck Capacity Requirement

Determining what size (capacity rating) forklift truck is required for handling your materials may require the assistance of a material handling professional. Basic information and principles of lift truck design are offered here to get you started.

The net capacity rating and type of lift truck that is required for the safe handling of your materials will take a number of factors into consideration.


The Counterbalance Principle

Forklift trucks work on the principle of a load counterbalanced over a fulcrum; the same principle as a seesaw.

The weight of the forklift truck counterbalances the load on the forks.

The fulcrum or pivot point of the "seesaw" is the centerline of the front wheels of the truck.


The Truck Capacity Rating defines the Maximum Load

The capacity rating of a forklift truck that is shown on the capacity rating nameplate defines the maximum load that the truck can safely handle.

The capacity rating of a forklift truck has two components: Weight and Load Center

The weight is simply the weight of the load.

The load center of the load is also known as the horizontal center of gravity of the load.

For uniform loads which have uniform weight distribution from one end to the other, the load center is in the middle or center of the load; i.e. at that point that is 1/2 of its length.

Since the standard pallet in North America is a 48" long pallet, most forklift trucks are rated to carry a load that has a given weight at a 24" load center on the pallet.


Too Much Moment Tips the Truck Forward

If a truck is loaded such that the combination of Load Weight and Load Center distance from the front of the truck creates more downward force than the truck is designed to handle, the truck will tip over forward.

This downward force in physics is termed moment.

For example, if a truck has a capacity rating of 4000 lbs. @ 24" Load Center, the maximum standard uniform load that the truck can handle is a standard 48" long pallet of material that has uniform weight distribution from one end to the other, and weighs 4000 lbs.

The moment of the maximum load that the truck can handle is 4000 lbs. x 24" = 96,000 inch-pounds.


Too Much Weight Tips Truck Over

If you pick up a load that weighs too much, it will create more downward force (moment) and cause the truck to tip over.

A truck with capacity rating of of 4000 lbs. @ 24" Load Center can handle a load that will create a maximum moment of 4000 lbs. x 24" = 96,000 inch-pounds.

Picking up a load that weighs 5000 lbs. and has a 24" Load Center will create a moment of 5000 lbs. x 24" = 120,000 inch-pounds.


Extended Load Center Tips Truck Over

If you pick up a load that has a load center that is longer than 24", the combination of weight and extended load center distance of the load can create a greater moment than the truck can handle and the truck will tip over forward.

If your truck capacity rating is 4000 lbs. @ 24" Load Center and you pick up a 4000 lbs. load that is 60" long and has uniform weight distribution from one end to the other, you are attempting to handle 4000 lbs. at a 30" load center:

Truck capacity rating = 4000 lbs. x 24" Load Center = 96,000 inch-pounds moment.

Moment of load = 4000 lbs. x 30" load center = 120,000 inch-pounds.


First, Determine Weights and Load Centers of Loads

In order to determine the correct capacity rating of lift truck that is required for moving your materials, you must know the weight and horizontal center of gravity of the loads that you must handle.

Given this information, you (we) can determine your forklift truck requirements.

For example:

If you want to handle rolls of carpet that are 12' long and weigh 1500 lbs., since a roll of carpet is a "uniform load"; i.e., it has uniform weight distribution from one end to the other, you would need a truck capable of handling a load that weighs 1500 lbs. and has a 72" load center.

A roll of carpet that weighs 1500 lbs. and has a 72" load center will generate a moment of 1500 lbs. x 72" = 108,000 inch-pounds.

Since forklift trucks are rated at 24" load center, in order to handle a load with 108,000 inch-pounds of moment, you will need a forklift truck with a capacity rating of 108,000 / 24 = 4500 lbs. @ 24" load center.

Moment of load = 1500 lbs. x 72" load center = 108,000 inch-pounds
Truck Capacity = 4500 lbs. x 24" load center = 108,000 inch-pounds


Other Factors

This method will get you to a good approximation of the size or capacity rating of the forklift truck that you will need.

However, there are other factors that must be taken into consideration in order to "fine tune" this calculation and insure that you purchase the correct truck.

It will be best to call us for consultation but here are some of the factors that must also be considered:

Lifting Height - The higher you must lift a load in order to stack or rack it, the higher the base capacity rating your truck must have, because the capacity rating of most trucks is reduced at higher lift heights. If you are going to lift your loads up to 20' (240") for storage in racks, you will usually need a higher capacity truck than if you are going to lift the loads up to 10' (120").

Attachments - If you want or need your truck to be equipped with an attachment such as side shifter, paper roll clamp, fork rotator, drum grab, or anything other than standard forks 48" or shorter, you will usually need a higher capacity truck because adding any attachment to a truck including long forks, can reduce its capacity rating. Adding an attachment is like adding a partial load to the truck. The attachment has weight and a horizontal center of gravity and thus it has a moment of its own which must be deducted from the basic moment capacity of the truck. Adding an attachment also often adds to the effective load center at which the loads will be handled.

Vertical Center of Gravity of Load - Handling loads that are taller than 48" and have a vertical center of gravity that is higher than 24" above the top surface of the forks, can also require more base capacity of truck in order to provide sufficient net capacity rating for handling the loads.

Configuration or Nature of Loads - Regardless of load weight, the size, configuration, or nature of the materials to be handled may dictate using a larger truck than otherwise may be needed for handling a standard pallet of similar weight.

Floor or Surface Conditions - Regardless of load weight, the floor or operating surface conditions may dictate using a larger truck.

Call us for expert advice and assistance in determining the correct truck for your needs.