U-shape, square or rock body: choosing a tipper body
Most tipper enquiries specify a volume — “I need 40 cubic metres” — and stop there. Volume is the easy number to name, but on its own it is close to meaningless. What you are actually buying is a shape, a floor thickness and a discharge angle, and those three decide whether the trailer earns money or sits in a workshop.
The mistake that costs the most
Start here, because it invalidates everything else if you get it wrong.
You order by volume. You are limited by weight.
| Material | Approximate density | 30 m³ weighs about |
|---|---|---|
| Dry sand | 1.5 t/m³ | 45 t |
| Wet sand | 1.8 t/m³ | 54 t |
| Crushed aggregate | 1.5–1.6 t/m³ | 45–48 t |
| Iron ore | 2.5 t/m³ | 75 t |
| Coal | 0.8 t/m³ | 24 t |
A 30 m³ body filled with wet sand is already at 54 tonnes — beyond what a standard three-axle trailer should legally carry in most of our markets. Fill the same body with coal and you are at 24 tonnes, with the trailer running half empty by weight.
So the right question is not “how many cubes” but “which material, and how heavy is it when wet”. Tell us the material and we will size the body so that full-by-volume and full-by-weight arrive at roughly the same moment. That is the only configuration where you are not wasting either payload or space.
The three body profiles
U-shape
A half-round floor with no internal corners.
Best at: shedding sticky material. Wet sand, clay, damp aggregate — the curve gives the load nowhere to key into, so it slides out cleanly at a lower tipping angle.
Also: the curved section is inherently stiff, so a U-shape can use thinner plate than a square body of the same capacity and still resist deformation. That is tare weight you get back as payload.
Weak at: volume efficiency for light, bulky material, and awkward for loading with a small excavator bucket that wants a flat floor.
Square (box) body
Flat floor, vertical sides, corners.
Best at: maximum volume in a given length, and easy loading. If you haul coal, wood chips, light aggregate or anything low-density, the extra cubes are worth more than the discharge advantage.
Weak at: sticky material packs into the corners and stays there. And corners are stress concentrations — a square body under heavy, sharp material needs internal stiffeners and thicker plate, which puts the tare weight back on.
Rock body
A heavy-duty square or shallow-U body with a thick floor, wear plate, and usually no external stiffeners in the impact zone.
Best at: surviving blasted stone dropped from an excavator. The floor takes the impact directly and the plate is specified to absorb it.
The cost: it is heavy. A rock body can add a tonne or more of tare against a standard square body, which comes straight off payload. Only order one if you genuinely load blasted rock from height. Quarry-crushed aggregate does not need it.
Where wear plate actually earns its money
HARDOX-type abrasion-resistant plate costs real money, and lining the whole body in it is usually waste.
The wear is not evenly distributed. It concentrates in three places:
- The front third of the floor, where material lands during loading
- The rear of the floor and the tailgate opening, where everything drags across during discharge
- The lower sides, for the first 300–400 mm above the floor
A sensible specification uses wear plate in those areas and standard structural steel elsewhere. That gets you most of the life at a fraction of the weight and cost. Ask for a lined floor with standard sides before you ask for a fully lined body.
Tipping angle, and a safety point worth stating
Standard discharge is 45–50°. More angle helps with sticky material, but a raised tipper is the least stable configuration a trailer ever adopts, and the higher it goes the worse it gets.
Two things matter more than a few extra degrees:
- Discharge on level ground. A trailer tipping on a side slope is how these vehicles turn over, and it happens with depressing regularity on unprepared sites.
- Material that has frozen or set will not release, and continuing to raise the body to force it is how the chassis gets bent. Break it loose, do not lift harder.
If your material is genuinely difficult, a U-shape body will do more for you than five degrees of extra angle.
What to tell us
- The material, by name, and whether it is loaded wet
- Its density if you know it, or the weight of a typical load
- How it is loaded — excavator height, drop height, bucket size
- Whether you run overloaded, and by how much in practice
- Ground conditions where you discharge — level yard or unprepared site
Get these right and the body specifies itself. Get the material wrong and you will own a trailer that is either always half empty or always over its axles — and see the guide on how many axles you need for why the second one is expensive.