Forklift Stability and the Stability Triangle Flashcards

What is the 'stability triangle' on a standard counterbalanced forklift?

Answer: The three-point suspension formed by the two front wheels and the rear axle pivot point

The stability triangle is the three-point support system created by the two front drive wheels and the single pivot point of the rear steering axle, defining the area within which the forklift's combined centre of gravity must remain.

On a counterbalanced forklift, where is the fulcrum point located?

Answer: At the front axle between the two drive wheels

The fulcrum point is at the front axle (between the two drive wheels), and it is the pivot point over which the forklift can tip forward if the combined centre of gravity moves in front of it.

What happens if the combined centre of gravity moves outside the stability triangle?

Answer: The forklift will tip over in the direction the centre of gravity has moved

If the combined centre of gravity moves outside the stability triangle, the forklift will tip over in that direction because there is no longer a support point to counteract the overturning force.

What is the 'combined centre of gravity' on a forklift?

Answer: The single point representing the combined weight distribution of both the forklift and its load

The combined centre of gravity is the single resultant point that represents the combined weight distribution of the forklift and the load it is carrying, and it must remain within the stability triangle for safe operation.

Which type of stability refers to the risk of a forklift tipping sideways?

Answer: Lateral stability

Lateral stability refers to the resistance to sideways tipping, which is primarily affected by the width of the rear axle, cornering speed, uneven surfaces, and off-centre loading.

Which factor directly reduces a forklift's longitudinal (forward/backward) stability?

Answer: Raising the load to a greater height while stationary

Raising the load to a greater height shifts the combined centre of gravity upward and forward, moving it closer to or beyond the fulcrum point and reducing longitudinal stability.

What is the primary purpose of the counterweight on a counterbalanced forklift?

Answer: To offset the weight of the load being carried and keep the combined centre of gravity within the stability triangle

The counterweight is positioned at the rear of the forklift to offset the weight of the load on the forks, preventing the forklift from tipping forward and keeping the combined centre of gravity within the stability triangle.

How does raising a load to a greater height affect forklift stability?

Answer: It reduces stability by raising the combined centre of gravity and increasing tip-over risk

Raising a load elevates the combined centre of gravity, making the forklift more susceptible to tipping in all directions, which is why loads must be lowered to the travel position before moving.

What effect does cornering at excessive speed have on a forklift's lateral stability?

Answer: It increases dynamic forces, shifting the combined centre of gravity outward and increasing tip-over risk

Cornering at excessive speed generates centrifugal forces that shift the combined centre of gravity outward toward the edge of the stability triangle, significantly increasing the risk of lateral tip-over.

How does operating on an uneven or sloped surface affect forklift stability?

Answer: It shifts the effective stability triangle and can cause tipping even with a correctly loaded forklift

Uneven or sloped surfaces tilt the entire forklift, shifting the effective position of the combined centre of gravity relative to the stability triangle and increasing the risk of tip-over.

What effect does under-inflation of forklift tyres have on stability?

Answer: It can cause uneven load bearing, reducing stability and causing premature tyre failure

Under-inflated tyres cause uneven load bearing across the tyre surface, which reduces the effective support base, increases rolling resistance, and can compromise the forklift's stability triangle.

When carrying an asymmetric or off-centre load, what stability risk is increased?

Answer: Lateral (sideways) tip-over risk, as the combined centre of gravity shifts to one side

An off-centre load shifts the combined centre of gravity to one side of the forklift, moving it closer to the edge of the stability triangle and increasing the risk of lateral tip-over.

Which condition MOST significantly reduces the stability of a forklift travelling with a raised load?

Answer: Travelling over a small raised edge such as a door threshold

Travelling over a raised edge or bump with a load at height causes a sudden jolt that can dramatically shift the combined centre of gravity, greatly increasing the risk of tip-over when compared to smooth, flat surfaces.

Why does adding an attachment (such as a side-shifter or extension) to a forklift reduce its rated capacity?

Answer: The weight and extended load centre of the attachment moves the combined centre of gravity forward, reducing stability and capacity

An attachment adds weight and extends the effective load centre distance, moving the combined centre of gravity further forward toward the fulcrum, which reduces the load the forklift can safely carry.

An operator is transporting a load and needs to turn a corner. What is the safest action regarding load height and speed?

Answer: Lower the load to travel height and reduce speed before entering the turn

Lowering the load to travel height and reducing speed before turning minimises the combined centre of gravity height and reduces centrifugal forces, keeping the centre of gravity well within the stability triangle.

What is the correct mast tilt position when travelling with a loaded forklift on level ground?

Answer: Mast tilted slightly back to secure the load against the backrest

Tilting the mast slightly back when travelling secures the load against the load backrest extension, preventing it from sliding forward and maintaining stability.

A forklift operator notices that the rear wheels are lifting off the ground during operation. What does this indicate?

Answer: The combined centre of gravity has moved in front of the front axle, indicating a forward tip-over risk

Rear wheels lifting off the ground means the combined centre of gravity has passed the front axle (fulcrum), and the forklift is on the verge of tipping forward — the operator must immediately lower the load.

Why should a forklift always carry loads as low as safely possible during travel?

Answer: To lower the combined centre of gravity and maximise stability within the stability triangle

Carrying loads as low as possible during travel lowers the combined centre of gravity, keeping it well within the stability triangle and significantly reducing the risk of tip-over.

What is the effect of driving a loaded forklift down a ramp with the load leading (forks facing downhill)?

Answer: It causes the combined centre of gravity to shift severely forward, greatly increasing forward tip-over risk

Driving down a ramp with the load leading causes the combined centre of gravity to shift significantly forward due to both the slope and the load position, creating a high risk of the forklift tipping forward over the front axle.

Which of the following actions would MOST improve forklift stability when operating on a slope?

Answer: Travelling with the heavy end (load or counterweight) facing uphill

Travelling with the heavy end facing uphill keeps the combined centre of gravity toward the uphill side of the stability triangle, reducing the risk of the forklift tipping forward or backward on the slope.