A 14-metre, 4-tonne telehandler cannot lift 4 tonnes to 14 metres. This is the most common, and most dangerous, misconception on construction sites. Understanding how to read the load capacity chart (load graph) in the cab is the fundamental difference between a safe lift and a catastrophic tip-over.
The three variables of a lift
Every load chart relies on three intersecting data points:
- Operating weight — the exact weight of the load being lifted.
- Lift height — how high the boom needs to extend vertically.
- Forward reach — how far the boom needs to extend horizontally away from the front tyres. This is usually the limiting factor.
What the side of the boom is telling you
Every telehandler carries a model designation that compresses two of the most important specifications into a short string: the maximum lift capacity in tonnes and the maximum lift height in metres.
- JCB 540-180 — 4.0 t maximum lift capacity, 18.0 m maximum lift height
- Manitou MT 1840 — 4.0 t / 18.0 m
- Merlo P40.13 — 4.0 t / 13 m
- CAT TH417D — 4.0 t / 17.0 m
- Bobcat T40.180SLP — 4.0 t / 18.0 m
Those two numbers describe the corners of the load chart, not the centre. They tell you: at zero forward reach with the boom retracted, you can lift 4 tonnes; at zero load you can extend the boom to 18 metres. You cannot do both at the same time.
How to read the chart
The load chart illustrates the machine's safe working envelope.
- The sweet spot — the maximum rated capacity (e.g. 4,000 kg) can only be lifted when the boom is fully retracted and raised to a specific, steep angle.
- Maximum reach — as you extend the boom horizontally, the machine's centre of gravity shifts forward. At maximum forward reach, that same 4-tonne machine might only be rated to safely lift 1,200 kg.
- Tyres vs stabilisers — most mid-to-large telehandlers have two separate load charts. One for lifting "on tyres" (free on wheels) and one for lifting "on stabilisers" (outriggers deployed). Stabilisers significantly increase the forward-reach capacity by anchoring the machine's centre of gravity.
A typical envelope for a 4 t / 18 m fixed-frame telehandler at the extremes:
| Configuration | Approximate safe lift |
|---|---|
| Boom retracted, 1 m reach, 1.5 m height | 4,000 kg (max rated) |
| 6 m reach, 6 m height | ~2,500 kg |
| 12 m reach, 14 m height | ~1,000 kg |
| Full 14 m reach, 18 m height | ~250 kg |
Those numbers come straight from a published JCB 540-180 load chart and are typical of every comparable 4 t / 18 m fixed-frame telehandler in the market.
Why capacity falls with reach
Telehandlers are essentially mobile cantilevers. As the boom extends forward and upward, the moment-arm increases — the load is now further from the rear axle and further from the boom-base pivot. The machine's stability is governed by the tipping line: when the moment of the load exceeds the moment of the machine's mass, the rear wheels lift.
The load chart is a simplified representation of the manufacturer's stability calculation under the standard conditions defined in EN 1459 (Rough-Terrain Trucks) — level ground, hard surface, forks at the standard load centre (500 mm), tyres at the specified pressure, and the operator seated. Any deviation from those conditions reduces real-world capacity.
Attachment de-rating
Site managers must ensure operators account for the weight of the attachment itself. If you attach a 300 kg concrete skip or a heavy-duty sweeper brush, that 300 kg must be deducted from the machine's overall lifting capacity for that specific boom position.
A 500 kg sweeper brush sitting at the end of the boom shifts the centre of gravity drastically. The load chart printed in the cab assumes a standard pair of forks at the standard load centre — anything else is a de-rated lift, and the operator must consult the attachment-specific load chart (which we supply with every hire that includes a non-standard attachment).
The LMI: traffic-light protection
Modern telehandlers (every machine manufactured since 2010 under EU Stage IIIA and later regulations) carry a Load-Moment Indicator (LMI). The LMI continuously calculates the load on the boom and compares it against the load chart for the current reach and height. The output is a three-state indicator:
- Green — within safe envelope; full motion available.
- Amber — approaching the safe envelope (typically 90% of capacity for that reach/height combination). An audible buzzer sounds.
- Red — at or beyond the safe envelope. Boom-out and lift functions are inhibited; only retract and lower remain available. The buzzer is continuous.
The LMI is a regulatory safety device, not an operator aid. Bypassing or disabling the LMI is a criminal offence under the Health and Safety at Work etc. Act 1974 and is treated as a Major Incident on every Tier-1 site we operate on. Any machine arriving on site with a sealed LMI override switch should be refused and reported.
Rotating telehandlers: the chart gets more complex
A fixed-frame telehandler has one load chart. A rotating telehandler — Manitou MRT, Merlo Roto, JCB 555-210R, Bobcat TR, Dieci Pegasus — has at least four:
- On wheels, no stabilisers — the most restrictive chart. Used for travelling and pick-and-carry.
- On stabilisers, slew limited to ±15° from front — the standard "construction" chart.
- On stabilisers, full 360° slew — the most permissive chart, but requires correct stabiliser deployment.
- In MEWP (man basket) mode — derated chart with hard limits on basket weight, and full LMI inhibition above the MEWP limit.
The LMI on a rotating telehandler senses the slew angle and dynamically swaps load charts as the turret rotates. It also senses stabiliser deployment via pressure switches on the outrigger jacks: if a single stabiliser is not fully on the ground at the manufacturer's specified pressure, the chart reverts to the most restrictive on-wheels chart.
This is why CPCS A77E (or NPORS N139D) is a separate ticket from the fixed-frame A77 / N139. The interaction between slew, stabilisers, and the four load charts is materially more complex than fixed-frame operation, and the consequences of getting it wrong are materially more serious.
Three rules for the operator
If you are reading this as a non-operator (a site manager spec'ing the right machine, or a foreman new to telehandlers), these are the three rules every operator we dispatch is trained to:
- Plan the lift, not the machine. The lift radius and height come first. Pick the smallest machine on whose load chart that lift sits in the green zone with at least 25% headroom.
- The chart is for new tyres on flat ground. Add a working safety factor. Wet ground, gradients, side-slope, gusty wind — every condition that deviates from "EN 1459 standard" reduces real-world capacity by 5-30%.
- Trust the LMI buzzer. When it sounds amber, retract the boom or lower the load before the next move. The LMI's response time is well under one second; the operator's response time is not.
In summary
The two numbers on the boom — capacity and height — describe the extreme corners of the load chart, not the working envelope. Real-world capacity at full reach and full height is typically 5-10% of the rated maximum. The LMI is a regulatory safety device, not an aid; it must never be bypassed. And on rotating telehandlers, stabiliser deployment is what unlocks the permissive load charts.
If you are unsure which chart applies to your specific lift, our regional operators are CPCS / NPORS-ticketed to plan the lift with you on the day. Get a quote [blocked] or browse our fleet [blocked] to pick the right machine for the radius.
This article is reviewed against the current EN 1459-3:2015+A1:2018 (Rough-Terrain Trucks — Variable-Reach) and HSE PM28 (Working Platforms on Telehandlers). Last review: 23 May 2026.
