Choose in this order: load and lifting points, then the route clearances, then the ground, then capacity, then duty class, then drive. Capacity is a result of those five inputs, not a starting point. A machine specified from the capacity column alone usually ends up either too wide for the aisle or too heavy for the slab.
Most straddle carrier enquiries arrive as a single number: “we need a 60-tonner” or “something for 40-foot containers”. That number is useful, but it hides the four or five constraints that actually determine the machine. Two carriers with the same rated capacity can differ by several metres in turning radius, by tonnes in unladen weight, and by a factor in cost.
The sequence below is the one we use in technical review. It is deliberately not the sequence in which buyers usually think, because the expensive mistakes happen early and only show up at the end.
1. Start with the load, not the capacity
Rated capacity is defined at a specific load centre. Move the centre of gravity away from that point — a 30 m precast beam, a coil on a saddle, an unbalanced module — and the usable capacity falls. The load diagram, not the headline figure, tells you what the machine can actually lift in your configuration.
Three load questions decide more than any other:
- What is the heaviest single lift? Not the average, and not the design load of the structure. The heaviest unit that will ever go on the machine, including lifting gear, spreader beam and any temporary bracing.
- Where is the centre of gravity? For a symmetric container it is the geometric centre. For a precast beam with one heavy end, or a tank with nozzles, it is not — and the frame has to be designed around the real position.
- How many lifting points, and are they synchronised? Long or flexible loads usually need four or more points with controlled synchronisation, otherwise the load twists as it is picked.
If the load is a standard container, the interface is already defined by ISO 668 and ISO 1496-1: 20 ft, 40 ft and 45 ft corner castings with known gross masses, so the spreader can be specified from a catalogue. If the load is not a container, the drawing replaces the standard, and the spreader or frame becomes part of the design rather than an accessory.
2. The eight numbers
Every straddle carrier specification reduces to these eight figures. Each one closes off some of the yard before you have chosen anything else.
| Number | What it decides | What it costs you if wrong |
|---|---|---|
| Rated capacity at load centre | The heaviest lift the machine can make in your configuration | Derating, a larger frame, or a redesign after the order |
| Portal clear width | Load width and the aisle the machine can enter | A machine that cannot pass between storage rows |
| Lift height | Stacking levels and clearance under conveyors or roofs | One stacking level fewer than planned |
| Wheelbase | Stability with long loads and the turning envelope | Tail swing that clips racks, columns or drainage |
| Turning radius | Whether corners and dead ends are usable | Reversing manoeuvres, lost cycle time, or a yard redesign |
| Maximum wheel load | The slab, joints and buried services | Slab failure, or reinforcement works nobody budgeted |
| Travel speed | Cycle time over the real route length | An extra machine to cover the throughput |
| Duty class | Structure, mechanism sizing and service life | Fatigue damage, or a machine built heavier than needed |
Published dimensions for the 35 t, 60 t and 80 t configurations are on the specifications page. Machines from 100 t to 500 t are engineered around the load and are not selected from a dimension table.
3. Clearance is a route question, not a machine question
Buyers compare overall width and height. The yard imposes something harder: the swept envelope of the machine with the load on.
- Height under load. A 35 t carrier is 5,450 mm high with a 1,550 mm lift, so the working height is around 7 m before the load is added. A machine that passes under a conveyor empty may not pass with a beam on board.
- Width on the move. The portal may be 5,100 mm wide while the load overhangs it. Loads wider than the portal need a wider frame, not a bigger crane.
- Corners. A long load turns a corner on a wider path than the machine. Measure the inside and outside sweep, not the aisle centreline.
- Doors, gates and ramps. Gate posts, cable trays, fire mains and lighting columns are the obstacles that appear late in the survey and are expensive to move.
The practical fix is a route drawing: a plan view of the yard with the machine outline, the load outline and the swept path at every turn. We ask for it on every project above 80 t, and it is worth drawing even for a standard 35 t machine.
4. The slab decides more than the catalogue
Ground pressure is not the laden weight divided by four. The number that matters to a structural engineer is the maximum wheel load, which depends on where the load sits, how many tyres carry it and how the suspension distributes it.
A 60 t machine on four solid tyres can impose a higher point load than an 80 t machine on eight tyres. The published 80 t configuration runs eight tyres, which spreads the load over more contact points instead of concentrating it.
- Joints, not just thickness. A slab that carries a forklift can still fail at a joint under a loaded carrier wheel. Edge distance and joint spacing matter as much as the design thickness.
- Buried services. Drainage runs, service trenches and duct banks are the usual failure points. The route should avoid them or be reinforced over them.
- Dynamic effects. Braking, steering and lifting add to the static wheel load, particularly on a semi-rough precast yard.
- Slope. Our 35–80 t models are rated at 3% gradeability laden and 5% unladen. A yard with a steeper ramp changes the machine or the route.
Send the slab drawing, joint layout and route and the wheel loads can be checked against the actual yard rather than a rule of thumb.
5. Duty class: the number nobody asks about
Duty class describes how hard the machine will work — hours per day, lifts per hour, and how often it lifts near its rated load. It is the difference between a machine sized for occasional yard moves and one sized for a three-shift production line.
The classification framework is set out in ISO 4301-1, with bridge and gantry cranes covered separately in ISO 4301-5, and the equivalent European design rules in FEM 1.001 and EN 15011. The output is a crane group and a mechanism group, which then drive plate thickness, bearing selection, brake sizing and gearbox rating.
Two failure modes follow from getting this wrong:
- Underspecified. A machine designed for light intermittent duty, run on a two-shift schedule, shows fatigue cracking at frame connections and premature gearbox wear within a few years.
- Overspecified. A machine designed for continuous heavy duty, used for a few moves a day, is heavier, slower and more expensive than the duty justifies — and the extra weight goes straight into the slab.
Give us the shift pattern, the lifts per hour and the share of lifts near rated load. That is enough to place the machine in the right group.
6. Diesel, lithium battery or hybrid
Three questions usually settle the drive choice:
- Is the machine indoors or in a confined area? If yes, exhaust emissions and ventilation become the deciding constraint, and battery or hybrid moves to the front.
- What is the shift pattern and the charging window? Battery drive needs a charging plan that fits the operating schedule, not a plan that assumes the machine can stop whenever the charger is free.
- Who maintains it? Diesel is the simplest option for remote sites with limited electrical support. Battery and hybrid need someone who can work safely on the pack and the inverter.
All three options are available across the 35–80 t configurations. The engine rating on the datasheet is the least important part of the decision; the duty cycle and the maintenance capability matter more.
7. Standards and documentation
A straddle carrier is a lifting machine, and the documentation matters as much as the steel. These are the standards that normally appear in a technical submission. Editions change, so we confirm the edition in force for the destination market at contract stage rather than quoting a year that may already be superseded.
| Standard | What it covers |
|---|---|
| ISO 4301-1 | Classification of cranes and mechanisms by utilisation and load spectrum |
| ISO 4301-5 | Classification of bridge and gantry cranes and their mechanisms |
| FEM 1.001 | Design rules for hoisting appliances, used where the customer's market requires it |
| EN 15011 | Bridge and gantry cranes: design, testing and marking for the European market |
| IEC 60204-32 | Electrical equipment of machines, hoisting-machine requirements |
| ISO 12488-1 | Tolerances for wheels and travel and traversing tracks |
| ISO 668 / ISO 1496-1 | Container dimensions, ratings and the corner-casting interface |
This table lists the standards normally referenced in a straddle carrier submission. It is not a claim of certification for any particular machine; the applicable set is agreed per project and per market.
8. The enquiry that gets a usable answer
Most quotation delays are not commercial. They are missing inputs. An enquiry that contains the following usually gets a dimensional proposal and a price in one round instead of three.
The load
Weight, dimensions, centre of gravity, lifting points and a drawing. Include the lifting gear if it travels with the load.
The route
Plan view, aisle widths, turning points, door and portal clearances, travel distance and surface type.
The ground
Slab thickness, joint spacing, drains, slopes and any posted weight limits along the route.
The duty
Shifts per day, lifts per hour, share of lifts near rated load and the expected service life.
With those four, the rest follows: capacity, portal width, lift height, wheel count, drive and duty group. Without them, any quotation is an assumption written down as a price.
Selection FAQ
Should I choose capacity first or the yard first?
The yard and the route come first, because they are the hardest to change. Capacity follows from the load. A machine that is right on capacity but too wide for the aisle is not a solution.
How much capacity margin should I allow?
Enough to cover the heaviest lift with its gear, at the real load centre — not a blanket percentage. Margin added for comfort becomes weight, cost and ground pressure, so it should be justified by a known future load.
Can one straddle carrier handle containers and precast?
Often yes, with two interchangeable lifting attachments: a telescopic spreader for containers and a frame or saddle for the precast units. The frame and the load diagram have to suit both, so tell us both duties from the start.
How long does a custom machine take?
It depends on the frame, the lifting gear and the testing programme. We confirm the schedule with the drawing package rather than quoting a lead time before the design is agreed.
Do you provide the wheel load calculation for our structural engineer?
Yes. Send the slab drawing and route and we return wheel loads per configuration, including the loaded and unladen cases, so the slab can be checked against the real machine.