A truck-mounted crane load chart at full outreach is a set of paired values where each cell expresses a maximum load at a stated horizontal radius, with the chart rated for a specific boom length, outrigger position and counterweight configuration that must be matched on the machine before any lift is attempted [S1][S3].
Operators should treat the chart as four intersecting variables: boom length, boom elevation angle, working radius and capacity, with gross capacity reduced by hook block, stowed jib, headache ball and rigging weight to arrive at the net capacity that the load must not exceed [S2][S3].
Chart structure: rows, columns and the loaded boom angle
On a typical truck-mounted crane sheet the boom lengths run across the top row and the working radius runs down the left column, with each intersecting cell giving the gross capacity for that combination, and the corresponding loaded boom angle stated in degrees so the operator can cross-check the value without measuring radius by hand [S2][S3].
Stowed jib deductions are listed as a separate row of values indexed against boom length, because a pinned boom or fly stowed on the base section still counts as parasitic weight at the boom tip and must be subtracted before the gross figure is compared to the load [S2].
Why capacity falls sharply at full outreach
Capacity and radius have an inverse relationship driven by load moment about the slewing centre, so on a 25 tm class boom truck a load of roughly 5,000 kg close in can collapse to around 1,200 kg once the boom is extended to its maximum reach, as documented for the HLM 25-5S configuration at 14.72 m [S4].
Gross versus net capacity: the deduction checklist
Capacity deductions that must be subtracted from the chart's gross value before comparing to the load include the main load block, the full lifting hook weight, jib weight whether stowed, erected or unused, the headache or overhaul ball, all rigging gear, and the hanging cable weight, and the manufacturer's own list on the specific chart always governs over generic guidance [S2].
With hook block, slings and a stowed jib typically totalling 200 to 600 kg on a mid-size boom truck, a chart line that reads 4,200 kg at full outreach can drop to a net capacity near 3,700 kg, which is the number that has to clear the actual load plus rigging [S2][S3].
Outrigger, counterweight and on-tyres configurations
Truck-mounted crane charts publish separate curves for stabiliser extended and set, for partial extension and for working on tyres only, and the legal stability margin built into each line is set by regulation: in California Title 8 Section 4923, for example, a commercial truck vehicle mounted crane with stabiliser extended and set is rated at 85% of tipping load, against 75% on tyres without outrigger support [S1].
Stability is the governing limit at long radius, not structural strength, so the operator should confirm the least stable direction is stated on the chart and that the stabiliser pads are bearing on a surface rated for the reaction load the chart implies, since a 50 tm lift at full outreach on soft ground can push pad pressure past 8 bar and punch through asphalt [S1][S3].
Reading at full outreach: a 60-second method
Step one is to identify the load weight including all rigging, then step two is to measure the horizontal radius from the slewing centre or outrigger centre to the hook, then step three is to select the chart line for the actual boom length and the outrigger or tyre configuration the truck is set up on [S5].
Step four is to read the gross capacity at that radius on the chosen line, subtract the deductions to get net capacity, and step five is to confirm the loaded boom angle printed in that cell matches the angle shown on the crane's inclinometer within roughly 1 degree, because a 2 degree discrepancy at long radius is enough to take the lift out of the chart envelope [S3][S5].
Comparing like-for-like between crane offers
When two crane offers are compared on paper, the comparison should be made at the same boom extension count and the same outrigger state, because a 2S boom and a 5S boom on the same base model produce different capacity curves across the full radius sweep, not just at the maximum outreach point [S4].
For marine and offshore variants the same rule applies, and the catalogue value quoted as a tonne-metre rating is a tilting moment, not a maximum load, so a 1,500 tm crane such as the HLRM 1500-2S is rated at 83,000 kg at 11.00 m, a figure that is meaningless without its paired radius [S4].
Failure modes and limits operators actually trip
The most common misreads at full outreach are using a chart line for stabilisers fully extended when only partial jacks are set, neglecting the stowed jib deduction on a truck with a folded fly, and trusting a one-degree angle readout when the boom is flexing under load, each of which can put the lift 5 to 15% over the charted net capacity [S1][S2][S3].
Wind, side load and dynamic factors are usually printed as notes rather than rows, and on most boom-truck charts a 30 km/h gust applies a multiplier that can shave another 10% off net capacity, so the verified pass is to keep net capacity above the rigged load by at least the margin the chart's notes require [S3][S5].
Verification signals to track on the next lift
For a follow-on audit the two verifiable signals are the chart revision date stamped on the cab-mounted plate and the serialised boom length printed in the chassis plate, both of which must match the chart booklet in the operator's station, and the on-site inclinometer reading compared to the loaded boom angle in the chart cell chosen for the lift [S1][S3].
Where the lift sits within 10% of the charted net capacity at full outreach, a third signal worth recording is the stabiliser pad pressure read on each jack, because a divergence of more than roughly 15% between pads usually indicates ground yield or partial extension and invalidates the chart line used [S1][S5].
For the relevant spec sheets and selection criteria, see truck mounted crane, truck mounted concrete pump, and electronic load.
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