Understanding Load Center Balance
Two boys walk onto a playground—Jim, who is a bit burly and Tom, who is scrawny survey the mulched area. Tom eyes the vacant see-saw and sees an opportunity.
“Hey,” Tom said to Jim. “I betcha if we both sit on that see-saw, I’ll lift you off the ground without jumping.”
“You kiddin’?” Jim snorted. “I’m way bigger than you; no way.”
“I’ll bet you a Coke I’m right,” Tom says confidently.
“You’re on,” Jim challenged.
Tom mounted one side of the see-saw. Jim effortlessly sat a third of the way in from the end and raised Tom high into the air. “Your move,” Jim said smugly, picturing the cold soda he’d be drinking soon.
Letting go of the handles and scooting backward. Tom scoots further and further off the edge of the see-saw. Then, it happened. Ever so slowly, Tom’s side began to dip, and Jim began to ascend. As he did, Jim was perplexed, leaving the ground and realizing he’d lost the bet.
“Hey, what gives?” Jim queried. “How did you do that? Tom smiled.
“Brains are better than brawn,” Tom replied. Jim frowned and quickly dismounted the see-saw causing Tom to crash to the ground.
“You win this time,” Jim said. “But remember, I can still beat you up.”
A Forklift Load Center
While it’s likely more than one moral can be derived from the story above, there’s an applicable forklift-related physics lesson. The idea of load center balance, crucial to understand when operating a forklift, closely parallels what was demonstrated above. Counterbalanced lift trucks may not look like it, but they act a lot like seesaws. The front axle is the fulcrum, the forks are one side of the see-saw, and the main body of the truck (complete with a heavy counterbalance weight) is the other side of the see-saw.
As you add weight to the forks in the form of carried objects, you exert downward pressure on that “half of the see-saw”. Jim in the example above learned the object being carried doesn’t have to outweigh the truck to tip it over. Position of the weight makes all the difference in the equation. Even movement of a few inches away from the front axle can mean hundreds of pounds of pressure change. It’s very important to understand the principles of load centering in order to avoid tipping, accidents or falling loads.
Every forklift has a manufacturer-provided data tag or “nameplate” installed that explains the maximum load capacity deemed safe for the forklift to carry (though specialized attachments can affect load capacity, so be sure to know what modifications may have been made to the lift truck). This weight capacity rating, typically listed as “Dimension B”, is based on a balanced load with a center of gravity. A balanced 48” x 48” cube of material with a center of gravity 24” out from the vertical part of the forks is probably not what you’re moving much of the time. Since the position and distribution of weight make a major difference. How do you know how much can really be carried?
It’s not too tough to estimate, thankfully there are calculations.
Two Load Center Calculations to Know
The standard load center is 24” out from the vertical face of the forks. Let’s say we want to know how much weight we can carry with a load center of 30. we divide 24” (standard load center) by 30” (actual load center) and then multiply it by the standard rated capacity of the forklift (let’s say 6,000 lbs.). We have calculated the new safe capacity. In this case, it was 4,800 lbs. So the equation is:
(standard load center / actual load center) x rated capacity ≈ safe capacity.
A load moment is when a load center’s distance from a fulcrum increase. This determines how much overturning force is being applied to the forklift, and is a product of load weight times distance from the fulcrum (i.e., load moment = weight x distance). For example, a forklift rated to carry 6,000 lbs at a 24″ would have a maximum load moment of 144,000 lbs.
This equation is useful for determining if an unusual load (e.g., one longer than 48” or with uneven weight distribution) can be handled safely. The weight in the example above has a maximum load moment of 144,000 lbs. Let’s determine how heavy a load would be with a 30” load center. Divide 144,000 lbs. by 30”. You soon realize the forklift can safely carry 4,800 lbs. at a 30” load center.
These examples showcase the insights you need to ensure safe loads without engaging in dangerous trial and error.
A Few More Tips to Remember
Load center balance may involve a little math from time to time, but it certainly requires no physics degree. Understanding the basic calculations above will get you most of the way to safe load balancing, and it is always advised that you estimate safe load capacity with an oversized load. Here are a few other pointers to keep in mind for safe operation, as well:
- Always distribute weight as evenly as possible, and move the center of gravity as far back on the forks as possible to maximize control and load capacity
- Load balance does not assure dynamic stability: Accelerating or stopping quickly, making turns too quickly or making them on inclines, and driving with raised forks are all recipes for trouble
- Never exceed safe capacity estimates, and play it safe if weight is close to capacity—it is better to decrease weight than tip over a truck, injure a driver or lose a load
They may be heavy and strong, but forklifts are still bound by the laws of gravity. Load or use them incorrectly and the consequences could be disastrous. Be smart, know your load center balance, and you should be in good shape!
Have questions about load center balance or other forklift-related matters? Contact us at (614) 896-2360.