Truck Crane

What is a Truck Crane

A truck crane, more precisely a truck-mounted telescopic crane, is a mobile lifting machine that bolts a rotating crane superstructure onto a wheeled road chassis. The superstructure carries a hydraulically extended telescopic boom, a hoist winch and wire rope, the slewing bearing that lets it rotate 360 degrees, and an operator cab. The carrier underneath has its own driving cab and engine for highway travel. This two-cab arrangement is the visual signature that distinguishes a classic truck crane from a single-cab rough-terrain crane or a small boom truck. Capacities in this class commonly run from about 30 tonnes to 160 tonnes.

The defining engineering trait of any mobile crane, the truck crane included, is that it lifts from wheels rather than from a fixed foundation. That means its safe load is limited by tipping stability as much as by steel strength. The machine must deploy outriggers to create a wide, rigid support footprint, then read its lifting limit from a load chart that changes with every radius, boom length, and outrigger setting. A pressure transmitter or a load cell can be sized once and forgotten, but a crane's rated capacity is a moving target that the lift planner recomputes for each pick.

The history of the mobile crane traces to the early twentieth century, when steam and then internal-combustion shovels and derricks were placed on truck and rail carriers to follow construction and railway work. The decisive modern shift was the hydraulic telescopic boom, which spread in the 1950s and 1960s and replaced the bolt-together lattice boom for medium-capacity road cranes, because a telescopic boom can be extended in minutes by the operator instead of assembled by a crew. The all-terrain crane, combining highway speed with all-wheel drive and steering, emerged in the 1980s from German makers and now anchors the high-capacity wheeled segment.

In application scale, the mobile crane family spans an enormous range. At the small end, a boom truck or knuckle-boom loader crane handles a few tonnes for delivery and utility work. In the middle, truck cranes and rough-terrain cranes of 30 to 160 tonnes do the daily work of steel erection, precast setting, mechanical installation, and tree and tank work. At the top, all-terrain cranes such as the Liebherr LTM 11200-9.1 reach 1,200 tonnes and hoist heights near 188 metres, tall enough to erect wind-turbine nacelles. No single crane covers this span; selection is the act of matching a duty profile to a capacity class and chassis type.

Four engineering metrics dominate truck-crane quality and total cost of ownership: rated capacity at the working radius (not just the headline maximum at minimum radius), system load chart strength across the radius envelope, road mobility and axle compliance, and serviceability of the boom, slew, and hydraulic system over a fifteen-to-twenty-year life. A crane chosen on headline tonnage alone, without checking capacity at the radius the job actually needs, is the most common and most expensive selection error in the field.

Mobile Crane Types

The mobile crane family divides into several distinct chassis types, each tuned to a different trade-off between road travel, off-road mobility, capacity, and setup time. Choosing the wrong type is a costly mistake: a rough-terrain crane cannot legally drive to a downtown site, and a truck crane cannot cross soft ground a rough-terrain crane handles easily. The table below compares the main mobile crane types across the parameters that drive the choice.

Truck crane (truck-mounted telescopic, often the TMS designation): a slewing telescopic crane on a commercial or purpose-built two-to-four-axle road chassis with a separate carrier cab. It travels at full highway speed and is the default choice when a single machine must drive itself between urban and suburban job sites without a transport convoy. The Grove TMS9000E, for example, is a four-axle, 110 US ton (99.8 tonne) truck crane with a five-section main boom reaching about 43.3 metres. Tadano's GT series covers the same role, with the GT-1200XL-2 rated 120 US tons.

All-terrain crane (AT): a multi-axle crane with all-wheel drive and all-wheel steering, built to travel highways at speed and then crawl across rough sites. ATs span the widest capacity band, from compact 40-tonne two-axle machines to the nine-axle, 1,200-tonne Liebherr LTM 11200-9.1. Multi-axle steering gives surprising maneuverability for the size, and the type dominates wind energy, refinery, and infrastructure work where the crane must both cover distance and lift heavy.

Rough-terrain crane (RT): a single-engine, single-cab crane on four large flotation tires, designed only for off-road job sites. Its compact wheelbase and four-wheel steering, including crab and coordinated steering, make it ideal for confined and uneven ground, and capacities reach roughly 150 tonnes. Because it has one engine sized for site work rather than highway cruising, an RT is not road legal and must be hauled to site on a trailer, which is the trade-off for its off-road agility.

Boom truck and loader crane: a smaller articulating or telescopic crane mounted behind the cab of a commercial flatbed truck, used to load and unload its own cargo and for utility and service lifts. Crawler crane: not a wheeled mobile crane at all but a tracked machine; it cannot drive on roads and is transported in pieces, yet it earns a place in the comparison because it competes directly with large all-terrain cranes on heavy lifts and offers true pick-and-carry capability under load. SpecForge catalogs the crawler crane and truck-mounted crane as separate leaf entries.

Boom, Stability, and Load Charts

Three coupled mechanics decide what a truck crane can lift: the boom that sets reach and height, the stability that resists tipping, and the load chart that encodes both into a usable limit. Understanding these is the difference between reading a tonnage number and planning a safe lift. The single governing equation is the lifting moment: load multiplied by load radius. Capacity falls as the load moves out because the same tipping moment is reached with a smaller load at a longer arm.

Telescopic boom: most truck and all-terrain cranes use a multi-section hydraulic telescopic boom of high-strength steel, with three to as many as eight nested sections that extend by cylinder and rope-reeving systems. A truck crane boom typically extends from roughly 10 metres retracted to 40 to 50 metres fully out; large all-terrain booms go much further, with the LTM 11200-9.1 telescopic boom running from 18.3 to 100 metres. Lattice extensions, swing-away jibs, and luffing jibs bolt onto the boom head to add reach and tip height, and luffing or fixed jibs let the crane clear an obstruction or reach over a structure.

Stability and the tipping fulcrum: a lifting crane tips about a line through its support points, the outrigger floats or the tire contact patches. The load chart capacity where stability governs is set as a fixed percentage of the load that would just begin to tip, the tipping load, providing a safety margin against the unknowns of ground, wind, and dynamics. The table below summarizes how the standards set those stability margins.

The stability margin is not arbitrary. Stability-governed ratings are determined under the SAE J765 Crane Load Stability Test Code, which defines how the tipping load is measured and how the percentage rating is applied. Note that not every cell on a load chart is stability-limited: at short radius and high boom angle, the boom steel or the hoist line strength becomes the limit, so those cells are structurally governed and the percentage margin does not apply. Many charts print stability-governed and structurally-governed cells in different weights so the planner can see which limit is active.

Reading the load chart: the chart is a grid of load radius against boom length, returning rated capacity in tonnes. It is specific to one counterweight configuration and one outrigger spread; a crane with several counterweight and spread combinations carries a separate chart for each. The capacity printed is gross, so the planner must deduct the weight of the hook block, slings, jib, and any auxiliary rigging to find the net load that can be hung. Capacity also splits by working area, over-front, over-side, and over-rear, because outrigger geometry makes the machine stronger in some directions than others. Never interpolate past the printed points, and never lift a load whose radius will grow during the pick beyond the charted limit.

Counterweight, Outriggers, and Standards

If the boom and load chart describe what a crane can reach, counterweight and outriggers describe what makes that reach safe, and the governing standards describe how both are verified. These three subjects are where most field incidents originate, because they involve setup choices the operator makes on the day rather than fixed design.

Counterweight: the slab or block ballast carried at the rear of the superstructure balances the load moment about the slew bearing, letting the crane use its structural strength instead of tipping. Each capacity and radius on the load chart is tied to a specific counterweight mass; lifting with less than the charted counterweight invalidates the chart. Counterweight scales with capacity: a 100-tonne truck crane may use 20 to 30 tonnes of ballast, while the Liebherr LTM 11200-9.1 carries up to 202 tonnes. Because that mass would breach axle-load limits on the road, large-crane counterweight is removed and hauled on a separate support truck, then reinstalled and pinned on site. A backward tip-over during boom-down or load-release is the classic symptom of lifting with too little counterweight, or releasing a load the ballast was sized to balance.

Outriggers: hydraulically extended beams with floats that transfer crane and load weight to the ground at a wide footprint, pushing the tipping fulcrum outward. Outrigger spread is the single biggest operator-controlled variable in capacity: going from fully extended to intermediate or retracted spread can cut over-side and over-rear capacity by 30 to 60 percent, and each spread has its own chart. The float sits on a pad or mat sized so that ground bearing pressure stays below the allowable soil capacity, because ground failure, not crane strength, causes the majority of mobile crane tip-overs. Outrigger setup, ground assessment, and pad sizing are therefore a core part of lift planning, not an afterthought.

The table below maps the principal standards that govern mobile and truck crane design, rating, and operation across regions. Cross-region projects often need conformity to more than one.

The rated capacity limiter: required by EN 13000 and by ASME B30.5 on most new mobile cranes, the rated capacity limiter (RCL), also called the load moment indicator (LMI), continuously computes the actual lifting moment from sensed load, boom length, and boom angle, compares it against the active load chart, and warns the operator and then stops aggravating motions before the rated moment is exceeded. The 2010 amendment to EN 13000 removed the simple master override key, capped override-mode motion at 15 percent of normal speed, and required a data logger to record operating data for incident analysis. The RCL is a protective backstop, not a planning tool: it cannot substitute for selecting the right crane, counterweight, and outrigger spread before the lift.

Key Specification Parameters

Comparing truck cranes on a spec sheet means reading past the single headline capacity to the parameters that decide whether the machine fits the job and the road. The same crane may publish dozens of figures, but a manageable set truly drives selection: rated capacity at radius, boom length and system length, hoist height, counterweight, outrigger spread, axle configuration and gross weight, and crane class. Each is explained below.

Rated capacity: the headline maximum capacity is quoted at the minimum radius (typically 2.5 to 3 metres) with full counterweight and fully extended outriggers, which is rarely the working condition. The LTM 11200-9.1, for instance, is rated 1,200 tonnes at 2.5 metre radius. The number that matters is capacity at the actual lift radius and height, read from the load chart, which can be a small fraction of the headline. Always compare cranes at the radius the job needs, not at minimum radius.

Boom and reach: two figures matter, the telescopic main boom length and the maximum system length with lattice extensions and jibs. A truck crane boom may run 11 to 50 metres telescopic; a large AT main boom reaches 100 metres, as on the LTM 11200-9.1, and over 180 metres of hoist height with extensions. Maximum hoist height (lift height) and maximum radius define the working envelope; a tall reach at long radius almost always carries a low capacity.

Counterweight and outrigger spread: total ballast mass and the available counterweight combinations, plus the maximum and intermediate outrigger spreads, determine which load charts the crane can use. More counterweight and wider spread mean stronger charts but heavier transport and a larger ground footprint.

Axle configuration, gross weight, and drive: for road-legal cranes the axle count, axle loads, and gross vehicle weight govern which roads and bridges the crane can travel and whether ballast must be removed for transport. The Grove TMS9000E sits on four axles at a gross vehicle weight near 86,056 lb (about 39 tonnes), while the LTM 11200-9.1 uses a nine-axle chassis with an 18 x 8 x 18 drive and steer configuration and active rear-axle steering. Engine power matters for gradeability and travel speed: the LTM 11200-9.1 carrier engine is rated 500 kW with a separate 270 kW crane engine.

Crane class and duty: under ISO 4301-1 a crane is classified by combining its class of utilization with its state of loading (load spectrum) into a group classification, and the hoist mechanism is rated M1 through M8. The class drives fatigue life, rope and bearing sizing, and inspection intervals. A general-duty truck crane that occasionally lifts near capacity is a lower class than a crane run in continuous heavy production, and running a crane above its design class shortens its safe life. Other parameters to confirm include line pull and rope speed, slewing speed, telescoping time, tail swing radius, and the protection rating of the control system.

Selection Decision Factors

To turn the preceding chapters into a specific crane choice, work the decision sequence below in order. Most selection mistakes come not from one wrong answer but from deciding capacity before the radius and ground are known. These steps double as an RFQ template for a purchase or a heavy rental.

1. Define the governing lift: establish the heaviest load, its radius from the crane center, and the required hoist height for the critical pick, including the worst case where the radius grows during the lift. Capacity at that radius, not headline tonnage, is the selection target.
2. Choose the chassis type: truck crane for road-mobile general lifting, all-terrain for long road moves plus heavy or off-road lifts, rough-terrain for confined off-road sites, boom truck for delivery and utility work. The road-versus-site trade-off usually decides this before capacity does.
3. Size capacity from the load chart: select a crane whose load chart at the working radius, boom length, counterweight, and outrigger spread covers the net load with margin, after deducting hook block, slings, and jib. Treat lifts above 75 percent of chart capacity as critical lifts needing a written plan.
4. Verify ground and outrigger setup: confirm allowable ground bearing pressure, size outrigger pads or mats accordingly, and check that the available outrigger spread supports the needed chart in the required working area (over-front, over-side, over-rear).
5. Check road and transport compliance: for road-legal cranes confirm axle loads, gross weight, height, and width against the route and bridge limits, and plan counterweight and jib removal and the support-truck convoy if required.
6. Confirm safety systems and certification: rated capacity limiter or load moment indicator per EN 13000 or ASME B30.5, anti-two-block, level indicators, and the regional conformity the project requires (CE and EN 13000 in Europe, ASME B30.5 and OSHA Subpart CC in the United States).
7. Match crane class to duty cycle: select an ISO 4301-1 group classification and mechanism class that fit the expected utilization and load spectrum, so a crane bought for occasional peaks is not run in continuous heavy production beyond its design group.
8. Total cost of ownership: purchase or rental rate plus mobilization and transport, setup labor, fuel, periodic inspection and load testing, wire-rope and component replacement, and resale value. A cheaper crane that is undersized at the working radius forces a second machine or a larger rental and quickly erases the saving.

One frequently overlooked dimension is manufacturer serviceability: parts availability for boom wear pads, slew bearings, hydraulic cylinders, and the RCL electronics; field service and load-test support; and software and load-chart updates over a fifteen-to-twenty-year life. Liebherr, the Tadano Group (including the Demag all-terrain line), and Manitowoc (Grove) maintain wide service and parts networks, while XCMG, SANY, and Zoomlion offer broad capacity ranges at lower price points with rapidly expanding international support. For a long-lived capital asset, service reach and resale value often outweigh a small difference in purchase price.