The doorway problem, stated plainly
A truck that lifts 6,000 mm is useless inside a container with 2,300 mm of headroom unless the forks can rise without the mast growing. That pre-growth travel is free lift, and it is the most under-asked question in truck selection after load center. Buyers who discover it late do so at the dock, with a container waiting; buyers who ask early get the mast specified around their doorways — the same ordering our aisle-width guide applies to width, applied here to height.
Duplex and triplex, in working terms
A duplex mast has two stages: one fixed outer rail and one sliding inner. A triplex has three, letting the forks travel further while the collapsed mast stays shorter. The trade is mechanical, not marketing: more stages mean more channels, more chains and more height per stage, at slightly more complexity and cost.
- Duplex, limited free lift: simplest and most robust; the mast grows almost immediately. Suits open warehouses with high doors.
- Duplex with full free lift: the forks reach a large fraction of the first stage before anything moves above the truck — the container and trailer configuration.
- Triplex: maximum lift from the shortest collapsed height; the choice when racking is tall and doors are low — a combination that arrives more often than buyers expect.
| Factor | Duplex (limited free lift) | Duplex (full free lift) | Triplex |
|---|---|---|---|
| Collapsed height | Lowest | Low to moderate | Low relative to reach |
| Maximum lift | Moderate | Moderate | Highest per collapsed height |
| Work under low heads | No | Yes — the container spec | Yes, plus tall racking after exit |
| Complexity | Minimal | Moderate | Highest of the three |
How the Granvolt line is specified
Our counterbalance line quotes 3,000 mm standard lift with maximum options of 4,500 mm on the EP18 and EP25 and 6,000 mm on the EP30; the DF line matches the 6,000 mm ceiling for yard stacking. The mast stage and free-lift configuration for each of those figures is stated per quotation, because the same model number can carry different masts — exactly why the RFQ asks for doorway and container headroom alongside racking heights. The mast types guide covers the 2-stage versus 3-stage basics; this article adds the free-lift dimension that the stage count alone hides.
Specifying free lift in an RFQ
- Measure the tightest headroom the truck must work under, loaded: container internal height, trailer nose, mezzanine soffits, door frames.
- State whether lifting happens under that headroom or only travel. Travel-under is the easier spec; lifting-under needs free lift plus derated capacity at height.
- Give the racking heights after exit. The triplex case exists precisely because both numbers are real on the same site.
- Confirm collapsed height against the doorway, including any beacon, camera or cab fittings that add to the truck's tallest point.
Four lines in the RFQ close the height question the way the load chart closes capacity: with numbers instead of surprises, and with the derated chart reading that the chart guide describes once the mast is chosen.
The container test, run in the yard
Whatever the specification says, run the container test before the truck is accepted: drive the truck into a container or trailer of the worst headroom you actually receive, lift a pallet to transfer height, and travel out. The test takes ten minutes and validates every number in this guide at once — collapsed height under the real head, free lift under the real ceiling, and visibility with the mast configured as it will actually work. If a mast option change falls out of the test, it falls out while the order is still a quotation rather than after the truck is yours, which is the whole reason the RFQ asks for doorway measurements alongside racking heights. Buyers who run the test never think about free lift again; buyers who skip it think about it every loading day.
Service life notes for taller masts
More stages mean more channels, chains and rollers, and the maintenance schedule should say so. Taller masts want chain inspection and lubrication on a shorter cycle, closer attention to channel wear where the stages run, and a hydraulic check that includes the extra lift circuit. None of this argues against the triplex; it argues for writing the taller mast’s extra care into the fleet’s maintenance schedule at delivery rather than discovering it as a pattern of small delays. The mast is the truck’s tallest wearing assembly, and on triplex configurations it repays scheduled attention with years of exactly-on-specification work at height — the same trade every component in this guide makes, priced honestly up front.
Frequently asked questions
What is free lift on a forklift?
The fork travel available before the mast channels begin to rise — the height you can lift inside a container, trailer or doorway without the truck getting taller.
Which mast works in a shipping container?
A full-free-lift configuration is the container specification: forks rise to roughly rack-beam height while the mast stays at its collapsed height.
Is a triplex mast better than a duplex?
Neither universally. Triplex reaches higher from a shorter collapsed height at more complexity; duplex is simpler and suits sites with generous doors.
What mast heights does Granvolt offer?
The EP line quotes 3,000 mm standard with up to 4,500 mm (EP18/EP25) and 6,000 mm (EP30) options; DF lines up to 6,000 mm. Stage and free-lift configuration are confirmed per quotation.
Does free lift change capacity?
Height derates capacity on the load chart regardless of mast type — read the derated figure at your working height, as the load chart guide describes.