TLILIC0003 Forklift Stability and the Stability Triangle — Questions and Answers

Question 1: What is the 'stability triangle' on a standard counterbalanced forklift?

The three-point suspension formed by the two front wheels and the rear axle pivot point (Correct answer)
The triangular shape formed by the mast, forks, and counterweight
The area between the load, the operator, and the rear axle
The three contact points between the forks and the load

Correct 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.

Question 2: On a counterbalanced forklift, where is the fulcrum point located?

At the centre of the rear axle
At the tips of the forks
At the front axle between the two drive wheels (Correct answer)
At the base of the mast

Correct 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.

Question 3: What happens if the combined centre of gravity moves outside the stability triangle?

The forklift's speed automatically reduces
The forklift will tip over in the direction the centre of gravity has moved (Correct answer)
The load capacity indicator will sound an alarm
The rear wheels will lift, but the forklift remains balanced

Correct 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.

Question 4: What is the 'combined centre of gravity' on a forklift?

The centre of gravity of the load alone
The centre of gravity of the empty forklift alone
The single point representing the combined weight distribution of both the forklift and its load (Correct answer)
The midpoint between the front and rear axles

Correct 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.

Question 5: Which type of stability refers to the risk of a forklift tipping sideways?

Longitudinal stability
Lateral stability (Correct answer)
Rotational stability
Dynamic stability

Correct 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.

Question 6: Which factor directly reduces a forklift's longitudinal (forward/backward) stability?

Using pneumatic tyres instead of solid tyres
Carrying a heavy load with the mast tilted fully back
Raising the load to a greater height while stationary (Correct answer)
Operating at low speed on a flat surface

Correct 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.

Question 7: What is the primary purpose of the counterweight on a counterbalanced forklift?

To increase the speed of the forklift when travelling without a load
To offset the weight of the load being carried and keep the combined centre of gravity within the stability triangle (Correct answer)
To provide additional braking force when descending ramps
To protect the engine from damage during collisions

Correct 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.

Question 8: How does raising a load to a greater height affect forklift stability?

It improves stability by raising the centre of gravity above obstacles
It has no effect on stability provided the load is within the rated capacity
It reduces stability by raising the combined centre of gravity and increasing tip-over risk (Correct answer)
It only affects stability if the load exceeds 500 kg

Correct 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.

Question 9: What effect does cornering at excessive speed have on a forklift's lateral stability?

No effect — forklifts are designed to corner safely at any speed
It increases dynamic forces, shifting the combined centre of gravity outward and increasing tip-over risk (Correct answer)
It reduces wear on the tyres and improves grip
It causes only the load to shift, not the forklift itself

Correct 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.

Question 10: How does operating on an uneven or sloped surface affect forklift stability?

It has no effect if the load is carried low
It shifts the effective stability triangle and can cause tipping even with a correctly loaded forklift (Correct answer)
It only affects stability when the load exceeds the rated capacity
Slopes improve stability by lowering the rear of the forklift

Correct 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.

Question 11: What effect does under-inflation of forklift tyres have on stability?

It improves cushioning and increases stability on rough surfaces
It has no effect on stability as long as the tyres are not flat
It can cause uneven load bearing, reducing stability and causing premature tyre failure (Correct answer)
It only affects steering, not stability

Correct 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.

Question 12: When carrying an asymmetric or off-centre load, what stability risk is increased?

Longitudinal (forward/backward) tip-over risk only
Lateral (sideways) tip-over risk, as the combined centre of gravity shifts to one side (Correct answer)
The risk of the mast collapsing under uneven stress
No additional risk, provided the total weight is within rated capacity

Correct 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.

Question 13: Which condition MOST significantly reduces the stability of a forklift travelling with a raised load?

Travelling slowly in a straight line on a flat, smooth floor
Travelling over a small raised edge such as a door threshold (Correct answer)
Having the mast tilted fully back while the load is at travel height
Operating in a well-lit, dry warehouse environment

Correct 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.

Question 14: Why does adding an attachment (such as a side-shifter or extension) to a forklift reduce its rated capacity?

Attachments increase the hydraulic pressure required, weakening the mast
The weight and extended load centre of the attachment moves the combined centre of gravity forward, reducing stability and capacity (Correct answer)
Attachments are not permitted in Australia and always void the rated capacity entirely
Attachments only reduce capacity if they weigh more than 50 kg

Correct 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.

Question 15: An operator is transporting a load and needs to turn a corner. What is the safest action regarding load height and speed?

Raise the load slightly before turning to clear any obstacles
Lower the load to travel height and reduce speed before entering the turn (Correct answer)
Maintain current speed to keep the load stable through momentum
Tilt the mast forward during the turn to lower the centre of gravity

Correct 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.

Question 16: What is the correct mast tilt position when travelling with a loaded forklift on level ground?

Mast tilted fully forward to keep the load low
Mast vertical (upright) with no tilt
Mast tilted slightly back to secure the load against the backrest (Correct answer)
Mast tilt is irrelevant provided the load is within capacity

Correct 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.

Question 17: A forklift operator notices that the rear wheels are lifting off the ground during operation. What does this indicate?

The rear tyres are under-inflated and need to be checked
The combined centre of gravity has moved in front of the front axle, indicating a forward tip-over risk (Correct answer)
The forklift's suspension system is functioning correctly
The load is correctly balanced on the forks

Correct 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.

Question 18: Why should a forklift always carry loads as low as safely possible during travel?

To reduce fuel consumption and wear on the hydraulic system
To lower the combined centre of gravity and maximise stability within the stability triangle (Correct answer)
To comply with road rules that restrict vehicle height
To prevent the load from blocking the operator's forward vision only

Correct 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.

Question 19: What is the effect of driving a loaded forklift down a ramp with the load leading (forks facing downhill)?

It is the safest method as the load acts as a brake
It causes the combined centre of gravity to shift severely forward, greatly increasing forward tip-over risk (Correct answer)
There is no difference in stability whether the load leads or trails on a ramp
It is only dangerous if the ramp exceeds a 10% gradient

Correct 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.

Question 20: Which of the following actions would MOST improve forklift stability when operating on a slope?

Increasing travel speed to reduce the time spent on the slope
Raising the forks to clear any surface irregularities on the slope
Travelling with the heavy end (load or counterweight) facing uphill (Correct answer)
Tilting the mast fully forward to keep the load near the ground

Correct 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.

Question 21: An operator picks up a load and finds the forklift feels very unstable and the rear begins to lift. What is the FIRST action they should take?

Accelerate forward quickly to redistribute the weight
Raise the load higher to clear the ground and then reverse slowly
Immediately lower the load to the ground without moving forward (Correct answer)
Apply the park brake and exit the forklift to inspect the load

Correct answer: Immediately lower the load to the ground without moving forward

Immediately lowering the load to the ground is the correct first action because it brings the combined centre of gravity back within the stability triangle, restoring stability before any further movement.

TLILIC0003 Forklift Stability and the Stability Triangle

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

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Sources & references

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