The center of gravity (CG) is the theoretical point on an object where all of its weight is concentrated. For a symmetrical load, this point is at its geometric middle.
For a forklift, the center of gravity is a dynamic point that shifts as the machine operates, lifts a load, or moves. When empty, a forklift's center of gravity is typically located between the rear wheels, toward the counterweight. When a load is lifted, the combined center of gravity of the forklift and its load shifts forward toward the front axle.
The Stability Triangle: Where the Center of Gravity Must Stay
For a forklift to remain stable, its combined center of gravity must always stay within an imaginary area called the stability triangle. This triangle is formed by drawing lines between three points:
The center of the rear axle (the pivot point).
The left front wheel.
The right front wheel.
If the center of gravity moves outside this triangle, the forklift will tip over.
Load Center and Its Impact on Capacity
The load center is the distance from the face of the forks to the load's center of gravity. Most forklifts are rated at a standard load center of 24 inches (for a standard 48-inch pallet).
If the load center increases (e.g., the load extends further forward on the forks), the forklift's maximum lifting capacity is reduced.
This is because the load's center of gravity is farther from the front axle, creating a greater load moment (weight x distance) that the counterweight must overcome.
Key Factors That Shift the Center of Gravity
The following factors can cause the center of gravity to shift, potentially moving it outside the stability triangle:
Load Weight and Distribution: An overloaded or unevenly loaded pallet shifts the center of gravity forward or sideways.
Lift Height: Raising the load higher raises the center of gravity, making the forklift more unstable and prone to tipping.
Mast Tilt: Tilting the mast forward or backward shifts the center of gravity.
Speed and Maneuvers: Sharp turns, sudden stops, or excessive speed can cause the center of gravity to shift dynamically.
Attachments: Adding an attachment (like a clamp or side-shifter) can add weight to the front and shift the center of gravity forward. This effectively de-rates the forklift's capacity. The manufacturer must be notified and a new data plate issued.
In summary: The forklift center of gravity is the balance point of the machine and its load. For safe operation, this point must always remain within the stability triangle. Factors like load center, lift height, and attachments all shift the center of gravity, affecting stability and reducing the safe lifting capacity.