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The Stability Triangle Prevents Telehandler Tip-Overs

The JLG equipment All Access Services provides uses a 4-step approach to teaching accident avoidance on telehandlers.  Here 4 important questions to ask for each:

Workplace Inspection: Is the workplace safe? What are the hazards?
Pre-Start Inspection: Is the machine safe visually? Is the machine safe functionally?
Proper operation: Am I operating safely? Do I have 360◦ awareness?
Proper shutdown: Is this a safe and secure location?

prevent telehandler accidents

The core to these 4 steps is a machine that remains balanced on a triangular footprint and lifts heavy weights to varying levels of height.  There are potential other dangers, but the key goal is to keep the telehandler upright.


The 2 front wheels and the rear-axle pivot point create a telehandler's triangular base.  The rear wheels are separate from the base because the near axle usually oscillates.  As long as the equipment's center of gravity (the point in the 3 dimensions around which the machine's weight is balanced) remains oriented inside the "stability triangle", the telehandler will remain upright.


stability triangle telehandler

While the boom is down, adding a load to the forks moves the center of gravity forward and down.  Lifting the load will move the center of gravity up and to the rear, and the same time causes the stability triange to minimize.  The hight you lift a load, the less margin of error the operator has because the stability triangle becomes smaller.  


A smaller stability triangle leaves little room for the center of gravity to move left or right if the frame is not perfectly level.  As an example, picture the center of gravity as a plumb bob hanging from the boom, you'll always have the center of gravity somewhere on a perfectly vertical line between a point on the boom and the center of the Earth.  If the telehandler frame's not level, the center of gravity will not be created over the machine's centerline.  But the stability triangle IS ALWAYS aligned with the telehandler centerline.

When the boom is raised and extended, the stability triangle is very small, the frame only has to be barely out of level to make the center of gravity drift to the other side of the triangle.  The "Laws of Physics" are as certain as gravity.  When the machine's center of gravity moves beyond the boundaries of the stability triangle, the telehandler will begin to tip.


On any job site, there are potential things and terrains that can affect the stability of a telehandler other than where you put the boom.  The operator may be on a 1-degree side slope, in a 5 MPH wind.  There may be icy roads under the wheels and 1 tire is a little low on air pressure.  If the telehandler goes over, there may not be a single cause.  It was a combination of factors that are all things that can be caught and corrected when you follow the Four Steps above.

A safe lift starts before putting the boom in motion, or even before the operator evalutes the job site for hazards.  Today's telehandlers are designed with a quick-attach coupler at the end of the boom.  Before installing an attachment, you need to make sure it's approved by the telehandler manufacturer and that it's capacity charge is in the cab of the telehandler for that particular model.  

 It's a violation with OSHA to run a machine if the proper load chart for that particular combination of machine and attachment isn't in the machine.  

It's also important to make sure forks haven't been tampered with, other than block forks, all forks need to be used in matched pairs.  Blocked forks are used in matched sets.
stability triange

The max capacity of a telehandler + attachment combination will be the lighest of these:  capacity stamped on teh attachment ID plate, the fork capacities stamped on the side of each fork (fork capacity X the number of forks on teh attachment), not to exceed the maximum on the attachment ID plate, maximum capacity indicated on the proper load chart, or the load rating of the telehandler.

When you test the limits of the load chart, it's important to do a test without a load on the forks; position the telehandler as you plan for the actual lift and run the forks up to the level of height the load needs to be placed.  By making a note of the boom extension and the boom angle at the extreme point of the lift, this will confirm the vertical height from ground level where the load is to be placed, and the horizontal distances from the front tires to where the load will be placed.

On the capacity chart, there is a horizontal line for the height of the lift and follow it over to where it intersects the line for the distance.  The point where the 2 lines meet should be within a load zone marked on the chart.  If it doesn't, the telehandler and attachment can't complete the lift.  The weight shown in the zone where the height and distance lines meet is the maximum capacity for this lift.  If the 2 lines meet on a boundary between zones, use the lighterof the 2 weights for this lift's limit.

Check the boom-extension and the boom-angle limits of the load zone on the capacity chart, when the load is in the air, no matter what happens, do not exceed those limits or the machine will tip.

All of the loads shown on capacity charts are assigned with the assumption that the machine is on firm ground with the frame level; forks positioned evenly on the carriage; load centered on the forks; proper size tires properly inflated, and the telehandler in good operating condition. Failing to comply with any of these conditions could tip the machine over.

Once you've determined that the lift is within the telehandler's and attachment's capabilities, it's time to set up the machine. Never engage a load or lift a load more than four feet above ground unless the telehandler is level.

Stop the machine on a stable surface in the best place to lift and place the load, set the parking brake, and shift the transmission into neutral. Before raising the boom, check the level indicator to see if the frame needs to be leveled from side to side. Many telehandlers have hydraulically tilting main frames that allow you to compensate for uneven terrain. Some have outriggers. Set the boom in the "carry" position — forks less than four feet off the ground — and level the machine. The machine should be ready to make the lift.

Never use the leveling system (sometimes called "frame level") or outriggers to level the telehandler after the load is more than four feet off the ground. After the load is in the air, if you discover that the telehandler is not level, bring the load back down before leveling the frame.

The higher up you go, the closer the sides of the stability triangle are — you don't have to go very far to move the center of gravity outside the triangle. If you use the frame level with a load high in the air, the boom only has to move a couple of degrees right or left and the machine may tip over.

If the telehandler isn't level when you reach the limits of the frame-leveling system, don't attempt the lift until the problem is solved. Reposition the telehandler on more-level ground or have the surface where it is standing leveled.

Always lift the load slowly, watching closely for changes in the footing or other conditions that could cause the frame to shift out of level. Don't move the machine once the load is more than four feet off the ground.

Placing a load at height requires a careful combination of multiple functions — boom down, boom out, while holding the forks level.

Once the lift is complete, the boom should be retracted and lowered to the carry position before the telehandler is moved.

Telehandlers are designed to handle rough terrain, but that doesn't mean they can be driven without regard for the terrain. Risk of tipping or load loss is much greater when traveling on slopes. If you must drive on a slope, keep the load low, tilted back, and proceed slowly with care. If the load exceeds the height of the carriage, a backrest extension will be needed. Before you get on the slope, downshift to a lower gear as engine braking will help control the telehandler's speed. Avoid turning on a slope.

Never drive across excessively steep slopes under any circumstances. Ascend and descend slopes with the heavy end of the telehandler pointing up the incline. When there's no load on the forks, the counterweighted rear of the machine is the heavy end, so you should back up slopes. When the telehandler is loaded, the front of the machine is the heavy end, so you should back down slopes.

The load or the forks cut the widest swath in a tight turn on a four-wheel-steer machine. But on the rear-pivot machine, it's the counterweight or the outermost rear wheel that's at the edge of the turning radius. In either case, the operator must look in the direction of travel to be sure the path is clear. But in cases where the operator is using a machine with rear-pivot steering, it's especially important to be aware of the counterweight.

It is vital that the operator maintain safe use of a telehandler. Accidents tend to happen when people neglect basic safety requirements in the name of speed.


Industry-leading training programs from the access industry leaders, bringing safety and confidence to your team: All Access Training Programs. Make sure you are compliant with the most up-to-date ANSI and OSHA regulations with expert-designed training plans. Telehandler operator and equipment service training, All Access offers comprehensive training to fit your telehandler needs.

About All Access Services

Serving construction projects throughout Southern California with heavy equipment rentals, we have 3 locations in San Diego, Orange County, and Riverside to serve our clients. Each location carries a fleet of scissor liftstelehandlersboom lifts, and forklifts available for rent at affordable rates. We strive to provide the best customer service in the industry and hope to earn your trust and business!

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