Hydraulic Multi-Axle Trailers & SPMT: When Are They Mandatory?

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Hydraulic multi-axle trailers are trailers made of coupled axle modules with self-levelling hydraulic suspension, pulled by a tractor unit. SPMTs are self-propelled modules. Both are needed when an indivisible package exceeds the axle-load limits of a lowbed trailer, or when precise positioning over short distances is required.

When to use hydraulic multi-axle trailers and SPMTs: a tarpaulin-covered project package on a trailer deck, hydraulic modules and an SPMT — *Hydraulic multi-axle trailers spread heavy loads over many axles for road transport; SPMTs handle short, precise moves in ports, plants and project sites.*

Table of contents:

I. How do hydraulic multi-axle trailers and SPMTs differ?

II. When is a standard lowbed trailer no longer enough?

III. 4 situations that call for hydraulic trailers or SPMTs

IV. How much can an 8-axle module trailer carry, and how many axles does a 300-tonne load need?

V. What permits are needed for a hydraulic trailer to operate?

VI. Frequently asked questions

VII. Conclusion

I. How do hydraulic multi-axle trailers and SPMTs differ?

The core difference is the power source: a hydraulic multi-axle trailer needs a tractor unit, while an SPMT drives itself using a power pack unit (PPU) mounted on the module.

Comparison of a tractor-pulled hydraulic module with a power pack and a self-propelled SPMT with numbered axles — *Hydraulic modules need a tractor or pusher and suit long-distance road moves. SPMTs have their own power pack and steer each axle, suiting short moves and manoeuvring in tight spaces.*

Both use hydraulic axle compensation: each axle rises and lowers independently to keep the deck level and spread the load evenly (Goldhofer THP/SL compensates 600 mm, Scheuerle SPMT 700 mm).

Criteria	Hydraulic multi-axle trailer (towed module)	SPMT (self-propelled module)
Power	Tractor unit at the front, optionally with a pusher	Diesel or electric PPU mounted on the module
Steering	Axle steering, large turning radius	All-direction steering: sideways, turning on the spot, diagonal
Positioning accuracy	Depends on the tractor driver	To the millimetre (Scheuerle states ±1–2 mm)
Rated load per axle (by manufacturer)	Goldhofer THP/SL: up to 45 t	Scheuerle SPMT: up to 60 t
Typical jobs	Moving transformers, boilers and tanks from port to plant	Roll-on onto barges, setting equipment on foundations, relocating cranes in a shipyard

Bottom line: for long road moves use towed modules; to turn, move sideways or place cargo precisely, use SPMTs. Many projects use both.

II. When is a standard lowbed trailer no longer enough?

A lowbed stops being viable when the load on each axle or axle group exceeds road limits, not just when the cargo is "very heavy".

Wind turbine tower section on cradles, carried by a hydraulic multi-axle trailer at a cargo yard — Long, heavy packages are spread evenly over many hydraulic axles to stay within permitted axle loads.

Under Circular 12/2025/TT-BXD (amended by Circular 19/2026/TT-BXD, consolidated text 26/VBHN-BXD):

Overweight cargo: when loaded, the gross weight of the vehicle or vehicle combination (including cargo) exceeds 48 tonnes (Article 10).
Axle limits: single axle ≤ 10 tonnes; tri-axle group ≤ 21–24 tonnes depending on axle spacing (Article 14).
Each vehicle may carry only 1 overweight unit (Article 12). Indivisible cargo cannot be split across two vehicles.

When a package is heavy enough to push each lowbed axle group over the limit, the practical solution is usually to add axles (or move part of the route to barge) - something hydraulic modules can do and a fixed lowbed cannot.

III. 4 situations that call for hydraulic trailers or SPMTs

Situation	Why a standard trailer cannot do it	Suitable equipment
1. An indivisible package too heavy for the lowbed's number of axles	Axle loads exceed limits, no circulation permit can be obtained, or bridge strengthening is too costly	Towed modules with added axles
2. Route with weak bridges or weak road foundations	The load must be spread over more axles, longer and wider	Towed modules coupled in 2 parallel lines
3. Roll-on/roll-off onto barges or pontoons	The barge deck rises and falls with the tide, misaligned with the quay level	SPMT (real-time hydraulic axle compensation)
4. Moves inside a plant, setting cargo on foundations	Tight space, turning on the spot, precise placement	SPMT

A public example in Vietnam: in 2022, Hyundai Vietnam Shipbuilding relocated two cranes weighing about 2,950 tonnes and 1,750 tonnes using 144 SPMT axle lines and 8 PPUs (Nha Dau Tu newspaper, 28/09/2022).

Have an indivisible package and not sure a lowbed is enough? Send H-Cargo the dimensions, weight and planned route, and we will analyse the options before you choose a vendor. Get a quote

IV. How much can an 8-axle module trailer carry, and how many axles does a 300-tonne load need?

There is no fixed figure. Payload depends on the permitted axle load at the actual travel speed, module self-weight, beams and the circulation permit. A common misunderstanding: the rated load applies at very low speed. Goldhofer states that the 45 t/axle rating of the THP/SL applies at 1 km/h; at road speeds the permitted axle load is much lower, for example the THP/SL-L drops to 26.1 t/axle at 20 km/h.

How to make a rough estimate:

Total load = cargo weight + beams, dunnage, lashing + module self-weight.
Permitted axle load = taken from the speed-based load chart of the exact model, then checked against the limit stated in the circulation permit.
Minimum number of axles = Total load ÷ permitted axle load, rounded up, plus a safety margin.

Illustrative example (rough calculation, not a quote or a real plan): a 300-tonne package, using Goldhofer THP/SL-L's 26.1 t/axle at 20 km/h. The cargo alone needs about 12 axles; adding module self-weight and beams requires more. An "8-axle module" is therefore not enough for a 300-tonne package on the road, even though the catalogue shows 8 × 45 = 360 tonnes.

Beyond the number of axles, check the centre of gravity: an off-centre package overloads one group of axles, so the survey must re-weigh the actual cargo rather than rely on the packing list.

Related articles:
- Break bulk vs Flat Rack vs Open Top: which option for your shipment
- Barges and pontoons for heavy cargo: when should you go by water instead of road?

V. What permits are needed for a hydraulic trailer to operate?

A module combination carrying overweight cargo must have a vehicle circulation permit and comply with the conditions stated in the permit (Circular 12/2025, Articles 8 and 12).

Item	Requirement	Legal basis
Vehicle inspection	The inspection certificate must show that the trailer is permitted to be coupled with modules	Article 11
Route survey	Mandatory when exceeding axle, gross weight or dimension limits for the road class	Articles 14, 15, Appendix XVI
Permit-issuing authority	The Department of Construction where the company is registered, or at the origin or destination	Article 24
Processing time	2 working days from receipt of a complete application	Article 23
Permit validity	Up to 30 days if the route requires strengthening, escort vehicles or a dedicated lane (up to 90 days without these conditions)	Article 22
Reason for choosing road	The application must explain why waterway or rail is unsuitable, or must be combined	Article 22

Note: the real timeline is longer than 2 days because route surveys, bridge strengthening and coordinating with power companies to raise lines take the most time. SPMTs running on public roads require prior consultation with the road authority on the applicable procedures; in practice SPMTs usually operate only within ports, plants or short controlled sections.

VI. Frequently asked questions

What is an SPMT and when is it used?

An SPMT (self-propelled modular transporter) is a self-propelled transport module with hydraulic suspension and all-direction steering. It is used to move very heavy packages over short distances, roll cargo onto barges or place equipment precisely.

How does a hydraulic multi-axle trailer differ from a lowbed?

A lowbed usually has a fixed number of axles. A hydraulic trailer adds modules to increase the axle count, spread the load and self-level the deck hydraulically, so it can carry much heavier packages with a lower load per axle.

How heavy must cargo be to require a circulation permit?

Under Circular 12/2025/TT-BXD, cargo is overweight when the vehicle combination including cargo exceeds 48 tonnes, and a circulation permit is then required. Vehicles exceeding axle or dimension limits also need a permit even if the total is under 48 tonnes.

How is hydraulic trailer hire priced?

By number of axles, hire days (including assembly and waiting days), distance and tractor units, plus surveys, permits, escorts and strengthening where needed.

VII. Conclusion

Choosing between a hydraulic multi-axle trailer and an SPMT depends on the route and the set-down point, not just the weight. Before confirming equipment, shippers should do three things: re-weigh the actual cargo and determine its centre of gravity; calculate the number of axles from the load chart at the actual travel speed rather than the catalogue rating; and survey the route, building permit and bridge-strengthening time into the project schedule.

With over 10 years of experience in oversized and heavy-lift transport, H-Cargo advises on hydraulic multi-axle trailers, SPMTs or combined waterway solutions for each project. Send the package dimensions, weight and planned route to receive a preliminary plan.

Author: Navy Ngo - Project team

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