Forklift Stability

It is not a mystery why forklifts tip over. It’s the result of gravity, weight, and motion. So, once you understand the principle, then you can do what is necessary to prevent it.

Forklifts are designed to avoid tip overs by counterbalance. As a result, they include the

following safety features:

· In order to create a counter balance, the body and cage of the lift are attached to the front or drive axle.
· The mast is allowed to pivot at or near the front axle.
· The steer axle is allowed to pivot at its center so the steer tires are always in contact with the ground.
· The brakes are located to the front drive axle.

A forklift can be fitted with different masts, wheels, tires, and fork tines to assist in stabilizing it.

A counterbalance forklift can tip only forward or sideways. When it tips forward the contact point of the drive axle tires and the ground serve as the pivot; when it tips toward the left side it pivots along a line from the left front tire contact point and the pivot point of the rear steer axle; when it tips toward the right it pivots along a line through the right front tire contact point and the pivot point of the rear steer axle. This defines the stability triangle.

The forklift center point (or center of mass) is where all its mass is located in three dimensions. When the forklift is stationary, the force of gravity is acting upon this point. So the lift will neither tip forward or toward its sides.

When weight is put on to the forklift tines, the center point and the load combines to move forward. If the load is too great, the lift will tip forward and the steer axle will lift off the ground.

As the forklift operator drives the forklift on a slope, or around a corner at some speed, or if he applies the brakes or accelerates the lift, gravity forces are generated that move the lift sideways, toward the front, or toward the rear. If the sum of all the forces acting on the center point is beyond the stability triangle of the lift, then the forklift will tip forward or sideways.

If a load that is too heavy is placed on the fork tines, then the center point of the forklift and the load combines to move forward, the lift will tip forward, and the steer axle lifts off the ground. However, if the center point is moving away from the two other tipping axis, then the forklift stabilizes as far as tipping sideways is concerned. So forklifts are more likely to tip sideways when they are empty.

If the forklift is loaded and heavy braking occurs, then the load will commonly fall off the tines. However, if the load is attached to the lift, then heavy braking will cause the lift to tip forward.

Tipping can be prevented if the forklift operator does not brake heavily, but rather regulates brake pedal pressure. Be aware that this will lead to increases in stopping distances.

Finally, there are four ways to test the counterbalance capability of a forklift.

1. Stacking with the mast set vertically and forks at maximum height.
2. Stacking with the mast at full rearward tilt and forks at maximum height.
3. Traveling with the mast at full rearward tilt and the forks lowered.
4. Traveling with mast at full rearward tilt and forks lowered.

Tests 1 and 3 help determine forward tip over stability, test 2 determines side tip over stability when the lift is loaded, and test 4 verifies side tip over stability when the lift is empty.