Truck mounted crane installation starts long before the first bolt goes in. The truck has to carry the crane’s own weight, keep its axle loads legal, give the crane a strong frame and enough length behind the cab, and drive its hydraulics through a power take-off (PTO). Only then is the crane fitted on a subframe, connected, and tested. Get the chassis wrong and no amount of careful fitting will fix it.
This truck crane installation guide sets out the truck chassis requirements for a crane first, using the real figures from the technical drawings of ten current BOB-LIFT cranes from 3.2 t to 12 t, then walks through the installation step by step. Every crane figure was read from the original drawings by Achord Chan, Product Operations Director at BOB-LIFT. The worked examples use stated assumptions.
Key takeaways
- Match the crane to the truck before you buy either. Our 3.2 t to 12 t cranes weigh 1,350 kg to 4,600 kg before oil, subframe and body are added.
- A crane mounted behind the cab puts most of its weight on the front axle. Check the front axle rating, not only the gross vehicle weight.
- Each crane needs a set length of chassis behind the cab. On the drawings below it runs from 750 mm to 1,400 mm.
- The PTO and pump must deliver the crane’s rated oil flow at its working pressure: 25 to 75 L/min at 20 to 30 MPa across these models.
- Finish with function, stability and load tests, and keep the records with the crane.
Can a truck mounted crane be installed on any truck?
No. A truck mounted crane, also called a loader crane or boom truck crane, can be fitted to many makes of truck, but only to a chassis that meets five conditions. The truck must have spare payload for the crane, axle ratings that can take its weight where it sits, a frame strong enough for the lifting forces, free frame length behind the cab, and a PTO that can drive the crane’s pump. A truck that fails any one of these is the wrong truck for that crane, even if the crane physically fits.
The table shows what each crane asks of the truck. All figures come from our technical department’s dimension drawings. A dash means the drawing does not give that value.
| Model | Boom | Max. capacity | Self weight | Installation space | Oil flow | Pressure | Recommended power | Oil tank | Outrigger span |
|---|---|---|---|---|---|---|---|---|---|
| SQ3.2ZA4 | Knuckle | 3,200 kg | 1,450 kg | 850 mm | 25 L/min | 25 MPa | 14 kW | 60 L | 2,250–3,513 mm |
| SQ3.2SA4 | Telescopic | 3,200 kg | 1,350 kg | 750 mm | 25 L/min | 20 MPa | 14 kW | 60 L | 1,720–3,120 mm |
| SQ5ZA4 | Knuckle | 5,000 kg | 2,386 kg | 1,050 mm | 35 L/min | 28 MPa | 22 kW | 100 L | 2,272–5,122 mm |
| SQ5SA4 | Telescopic | 5,000 kg | 2,400 kg | 800 mm | 32 L/min | 21 MPa | 18 kW | 100 L | 2,293–5,593 mm |
| SQ8ZA4 | Knuckle | 8,000 kg | 3,050 kg | – | 40 L/min | 28 MPa | 25 kW | 160 L | 2,310–5,610 mm |
| SQ8SA4 | Telescopic | 8,000 kg | 3,600 kg | 1,100 mm | 55 L/min | 26 MPa | 30 kW | 160 L | 2,290–5,990 mm |
| SQ10ZA6 | Knuckle | 10,000 kg | 3,700 kg | – | 40 L/min | 30 MPa | 30 kW | 160 L | 2,310–5,610 mm |
| SQ10SA4 | Telescopic | 10,000 kg | 3,800 kg | 1,100 mm | 63 L/min | 26 MPa | 37 kW | 200 L | 2,290–5,990 mm |
| SQ12ZA4 | Knuckle | 12,000 kg | 4,480 kg | 1,400 mm | 55 L/min | 28 MPa | 30 kW | 160 L | 2,316–5,706 mm |
| SQ12SA4 | Telescopic | 12,000 kg | 4,600 kg | 1,100 mm | 75 L/min | 26 MPa | 45 kW | 200 L | 2,300–7,500 mm |
Truck chassis requirements for a crane
Check these five requirements in order. The first two are about weight, the third is about strength, and the last two are about the space and power the crane needs.
1. Payload: the crane comes out of the truck’s carrying capacity
Everything you add to the chassis reduces what the truck can carry. Start with the truck’s gross vehicle weight rating (GVWR), subtract the chassis-cab weight, and then subtract the crane, its hydraulic oil, the subframe and the body. What is left is your real payload.
The crane is the biggest item. The SQ10SA4 10-ton telescopic crane weighs 3,800 kg on its drawing, and its 200 L oil tank adds roughly 175 kg more when full, since typical mineral hydraulic oil weighs about 0.87 kg per litre. The subframe and body depend on the build, so weigh them or take them from the body builder’s drawing rather than guessing.
2. Axle loads: check the front axle, not just the total
Most truck mounted cranes sit directly behind the cab, close to the front axle. That puts most of the crane’s weight on the steering axle, and the front axle rating is often the first limit a build hits, even when the total weight is well inside the GVWR.
The split follows simple leverage. With a wheelbase L and the crane’s centre of gravity a distance a behind the front axle, the front axle carries the crane weight × (L − a) ÷ L, and the rear axle carries the rest.
Worked example (assumed truck dimensions). Take the SQ10SA4 at 3,800 kg on a two-axle truck with a 4,700 mm wheelbase, and assume the crane’s centre of gravity sits 1,700 mm behind the front axle. The front axle takes 3,800 × 3,000 ÷ 4,700 ≈ 2,430 kg and the rear axle about 1,370 kg. Almost two thirds of the crane, about 64%, lands on the steering axle. Add that to the chassis-cab’s own front axle weight and compare the total with the front axle rating on the truck’s plate. Use your truck’s real dimensions, and ask us for the crane’s centre of gravity, when you do this for your build.
Mounting the crane at the rear of the body moves its weight onto the rear axle instead, but it can leave the steering axle too light when the truck is empty. Truck makers set a minimum front axle load for safe steering and braking, so check both the loaded and the empty case.
This calculation is a first estimate to see whether a crane and a truck can work together. It does not replace the full weight calculation by the body builder, with the crane, oil, subframe, body, outriggers, fuel and crew included, checked against the truck maker’s body builder guidelines and the vehicle approval required where the truck is registered.
3. Frame strength and the subframe
When the crane lifts, the slewing torque and the lifting moment go into the truck frame through the crane base and outriggers. On their drawings, the ten cranes above are rated from 6.8 t·m (SQ3.2ZA4) to 33 t·m (SQ12SA4). The chassis frame rails, on their own, are not designed to take that twist.
A subframe, a steel frame between the crane and the chassis rails, spreads the crane’s loads along the frame and stiffens it against twisting. Whether you need one, and how long and how strong it must be, depends on the crane’s moment and the truck’s frame section. Two sources decide it: the crane maker’s mounting drawing and the truck maker’s body builder guidelines. The body builder guidelines also say where you may drill the frame and which fasteners to use. As a rule, never weld to or drill the chassis frame flanges unless the truck maker allows it.
4. Installation space behind the cab
Each crane needs a clear length of frame for its base and outrigger box. Our drawings call this the installation space: 750 mm for the SQ3.2SA4, 800 mm for the SQ5SA4, 1,100 mm for the 8 to 12 t telescopic models, and 850 mm to 1,400 mm for the knuckle boom models that list it. Measure the free frame length behind the cab, allowing for the cab’s tilt clearance, the exhaust, the fuel and air tanks, and the battery box, which often have to move.
Everything behind the crane is your body length. Subtract the installation space and any gap you need from the frame length behind the cab to see how long a deck you can still fit.
5. PTO and hydraulics: flow, pressure and power
The crane runs on hydraulic oil from a pump driven by the truck’s PTO. The pump must deliver the crane’s rated flow at its working pressure, and the PTO must handle the torque. Our drawings give three figures for this: oil flow, system pressure and a recommended power.
The recommended power includes a margin. Hydraulic power in kilowatts is pressure in MPa × flow in L/min ÷ 60. For the SQ10SA4 that is 26 × 63 ÷ 60 ≈ 27 kW of oil power, against a recommended 37 kW. For the SQ10ZA6 10-ton knuckle boom crane it is 30 × 40 ÷ 60 = 20 kW against a recommended 30 kW. The gap covers pump and PTO losses, so size the PTO to the recommended figure.
Flow sets the pump size. Flow equals pump displacement × pump speed. If the PTO turns the pump at 1,000 rpm, the SQ10SA4’s 63 L/min needs a pump of about 63 cm³ per revolution, plus a little for the pump’s own losses. A different PTO ratio or engine speed changes that number, which is why we ask for the PTO data before we confirm a match.
Outriggers and ground space
The crane’s load chart assumes its outriggers are fully extended and on firm, level ground. The span on our drawings goes from about 1.7 m retracted on the SQ3.2SA4 to 7.5 m fully extended on the SQ12SA4. Check that your usual job sites have that width, and that the body and fuel tanks do not block the outrigger legs. Our guide on how to read a crane load chart explains why the chart only applies in the set-up it was drawn for.
Crane installation on a truck, step by step
Once the chassis matches, the installation follows six steps. It should be done by a qualified body builder or crane installer working from the crane maker’s mounting drawing and the truck maker’s body builder guidelines.
Step 1: Confirm the crane and truck match
Collect the truck’s data: make and model, wheelbase, GVWR, front and rear axle ratings, chassis-cab weight on each axle, frame rail section, free frame length behind the cab, and the PTO options with their output ratio and torque rating. Run the payload and axle load checks above with the crane’s figures. If the numbers do not work, change the crane or the truck now, not after the crane arrives.
Step 2: Prepare the chassis
Clear the mounting area. Move the fuel tank, air tanks, battery box or exhaust where they are in the way of the crane base or outriggers, following the truck maker’s rules for relocating them. Check the frame for damage or old repairs.
Step 3: Fit the subframe and the crane
Fit the subframe to the chassis rails with the clamps, brackets or shear plates the mounting drawing specifies. Lift the crane onto the subframe with a lifting device rated for its weight, line it up with the truck’s centre line, and fasten it with the specified bolts tightened to the specified torque. Keep a written torque record, because the crane manual sets when these bolts must be re-checked after the first period of use.
Step 4: Connect the PTO, pump and hydraulics
Install the PTO and pump, then run the suction, pressure and return lines to the crane and the oil tank. Keep hoses away from the exhaust and sharp edges, and clamp them so they cannot rub. Fill the tank with the hydraulic oil grade the crane manual specifies, and bleed the air from the system.
Step 5: Wire the controls and safety devices
Connect the PTO switch in the cab, the crane’s control circuits, the overload protection and any indicators, such as a warning that the outriggers or boom are not stowed. Fit an interlock that stops the truck being driven, or at least a cab warning, when the outriggers or boom are out of their stowed position, and follow the truck maker’s rules on driving with the PTO engaged.
Step 6: Test, inspect and record
Run every crane function without load: slewing, boom up and down, extension and outriggers. Check for leaks and confirm the safety devices work. Then carry out the stability and load tests required by the standard you build to and by the crane manual. In Europe, loader cranes are built and tested to EN 12999. In Great Britain, LOLER 1998 regulation 9 requires lifting equipment whose safety depends on its installation to be thoroughly examined after installation and before it is first put into service. In the United States, articulating boom cranes follow ASME B30.22 and telescopic boom cranes on trucks fall under ASME B30.5, and where OSHA’s construction crane rules apply, 29 CFR 1926.1412(c) requires a qualified person to inspect the equipment after assembly. Re-weigh the finished truck on each axle and keep the weight, torque and test records with the crane.
Do not apply a fixed rule to the crane’s working area. Some guides say, for example, that a crane can lift only about half its rated capacity over the cab, or that the full load chart always applies behind the truck. There is no general percentage: what a crane may lift in each slewing sector depends on that crane, its outrigger setup and the truck it is mounted on. Use the crane’s own load chart and the working-area limits in its manual, and confirm them in the stability test after installation.
A truck mounted crane is built for vertical lifting. Some sources present side loading as a strength of knuckle boom cranes and give dragging a load as an example. Dragging a load or pulling sideways puts forces on the boom, the slewing gear and the truck frame that the load chart does not cover, so do not do it unless the crane manual specifically allows it.
What BOB-LIFT checks before a crane ships
We test our cranes at the Xuzhou factory before delivery, and our product pages show a video of how we test them. When you send an enquiry, our form asks whether you already have a truck and for the truck model and chassis specifications. We use those to check payload, installation space and the PTO’s flow and pressure against the crane’s drawing, and we confirm the match when we quote. If the numbers do not work, we tell you before you order.
Frequently asked questions
How much payload does a truck mounted crane take?
Its self weight plus its oil, the subframe and any changes to the body. On our drawings, self weight runs from 1,350 kg for the 3.2 t SQ3.2SA4 to 4,600 kg for the 12 t SQ12SA4. A full 200 L oil tank adds roughly 175 kg on top.
Does every truck crane need a subframe?
Almost every crane of this size needs one, because the chassis rails alone are not built to resist the crane’s lifting moment and slewing torque. The crane maker’s mounting drawing and the truck maker’s body builder guidelines set its size. Do not leave it out to save weight.
Where should the crane be mounted on the truck?
Behind the cab is the most common position. It keeps the deck free and the crane can reach over the whole body, but it loads the front axle. A rear mount loads the rear axle and suits jobs where the crane works off the back of the truck. Choose the position from the axle load calculation and the way you unload.
What PTO does a truck crane need?
One that can drive a pump giving the crane’s rated flow at its working pressure, with power to spare. On our drawings that runs from 25 L/min at 20 MPa with 14 kW recommended for the SQ3.2SA4, up to 75 L/min at 26 MPa with 45 kW recommended for the SQ12SA4.
Can I do the crane truck installation myself?
Only if you are a qualified installer with the right lifting equipment and the mounting documents. Mistakes in fastening, hydraulics or stability show up under load, when they are most dangerous. Many buyers have the crane fitted by a local body builder, who also handles registration or inspection where the law requires it.
Crane installation checklist
- Payload left after crane, oil, subframe and body is enough for your loads.
- Front and rear axle loads stay within their ratings, loaded and empty.
- Subframe designed to the crane’s mounting drawing and the truck’s body builder guidelines.
- Free frame length behind the cab covers the crane’s installation space.
- PTO and pump give the rated flow and pressure, with the recommended power.
- Outriggers can deploy fully on your usual sites.
- Function, stability and load tests done and recorded, axles re-weighed.
The main drawing figures for each model are listed on its product page in our truck mounted crane range. To compare the two boom types for your truck, read our guide to knuckle boom vs telescopic boom truck cranes. Send us your truck’s data and we will check the match with you.
