In short: Q345 is the standard main beam steel on our builds and T700 is the upgrade. The higher grade lets the same rigidity be reached with less material, so the trailer sheds tare – but it only earns its place where the load and the duty cycle actually use the extra capacity. On light road work it is tare you carry every trip.
Steel grade is one of the largest single line items in a trailer quote and one of the least understood. Buyers often assume the higher number is automatically better. It is not – it is a trade against tare, and the trade only pays where the duty cycle collects on it.
What the two grades are in a trailer
Q345 is a structural high-tensile steel and it is what we build main beams from as standard, welded with automatic submerged arc processes. Q345B is the same family with tighter impact-testing requirements, and it is what the U-shape mining build uses. T700 is a considerably stronger high-tensile grade, and we specify it on builds where the customer’s duty cycle justifies it.
Neither grade is “the good one”. They are different points on a strength-to-weight curve.
The sections we actually publish
Grade is only half the story – the other half is the section cut from it. These are the published main beam sections across our range, all at 500 mm height:
- 25-35 CBM rear dump: upper flange 12 mm x 140 mm, middle web 8 mm, lower flange 12 mm x 140 mm.
- 3-axle skeleton and container chassis: top flange 18 mm x 140 mm, middle 14 mm, bottom 20 mm x 140 mm.
- U-shape mining rear dump: upper plate 16 mm, middle web 10 mm, lower plate 18 mm.
- Container flatbed: top plate 10 mm, middle 8 mm, bottom 10 mm.
A thicker section in the same grade carries more. A stronger grade reaches the same stiffness with a thinner section. Those are two different ways to buy capacity and they cost differently.
Which model uses which published section
The sections above are not abstract: each one belongs to a specific build. If you are weighing grades for a particular job, start from the model:
- 12 / 8 / 12 mm x 140 mm: the 3-axle rear dump semi trailer, 25-35 CBM, our standard road-haul tipper.
- 18 / 14 / 20 mm x 140 mm: the 3-axle skeleton container semi trailer, 40ft and the 40ft skeletal container chassis, where the beam carries concentrated twist-lock loads rather than a spread deck load.
- 16 / 10 / 18 mm: the 4-axle U-shape rear dump trailer, 80-100 t, the mining build specified around impact tolerance rather than highway efficiency.
- 10 / 8 / 10 mm: the container flatbed semi trailer for 20ft, 40ft and 45ft boxes, where the load spreads along the deck.
Heavier duty cycles scale the same logic up: see the 60-100 t heavy-duty lowbed and the wider dump and tipper range.
Where T700 earns its place
Our clearest case is a mining fleet order shipped to Uzbekistan in July 2026, where both the dump box and the main beams were fabricated from T700 instead of the common Q345. The reasoning was not marketing:
- A mining fleet measures a trailer in cycles, not kilometres. Loading happens from a face shovel or an excavator, which concentrates load in one place; discharge happens on uneven ground and often on a slope.
- Both conditions load the frame in ways a road-haul tipper never sees, so the build was specified around impact tolerance rather than highway efficiency.
- A stronger section reaches the same rigidity with less material, so the tipping body stays stiff while shedding tare it would otherwise carry on every trip. On a fleet running cycles, that trade repeats hundreds of times.
The full record is in that delivery case and in the U-shape mining model.
Where Q345 is the right answer
- Road haul on sealed surfaces. If the trailer spends its life on highways and in yards, the peak impact loads that justify T700 never arrive.
- Light or mixed cargo. Capacity you cannot legally or physically use is tare you carry for nothing.
- Budget-constrained first orders. On a one-unit trial, the money is usually better spent on axle rating or brakes than on steel grade.
- Markets where repair is crude. A heavier conventional section is more forgiving of field welding than a high-tensile one, which matters if your only workshop is a roadside operation.
What to decide before the grade
Our own case note puts the order of decisions plainly: fix the required struck volume first, then size the steel grade around it. Chasing the grade before you know the volume is how buyers end up with the wrong trailer at a higher price. Tell us the material, the daily tonnage, the loading method and the ground you tip on, and the grade follows from those answers.
Questions to ask any supplier about the beam
- What grade is the main beam – and is it the same grade for the box?
- What are the actual plate thicknesses, top, middle and bottom?
- What is the beam height?
- How is it welded – manual or automatic submerged arc?
- If T700 is quoted, what is the tare saving and where does it come from?
A quote that names a grade but no section has not told you what you are buying. The same logic applies to axle brand and rating and to suspension choice.
FAQ
Is T700 always better than Q345?
No. T700 lets the same rigidity be reached with less material, which reduces tare. It pays where the duty cycle loads the frame hard. On light road work it is extra cost for capacity you never use.
Can I have T700 only in the main beam?
Specification is set per order, and on the mining build above the box and the beams were both T700. Tell us the duty cycle and we will propose what should and should not change rather than quoting the whole trailer in the most expensive grade.
Does the beam get cut to fit a container?
No. The main beam leaves the factory as one welded structure whatever the shipping form – see what CKD actually means.
What beam height do you build?
500 mm across the range, with the plate thicknesses set per model and per order.
Do you use Q345 or T700 for a flatbed trailer main beam?
Q345 is the standard grade across our range, including the container flatbed, whose published section is 10 / 8 / 10 mm. T700 is specified only where the duty cycle justifies it. Tell us the load and the ground you tip on and we will say whether it pays.
Key facts
- Q345 is our standard main beam steel; Q345B is used on the U-shape mining build; T700 is specified where the duty cycle justifies it.
- Main beam height is 500 mm across the range.
- Published sections: 12 / 8 / 12 mm x 140 mm (25-35 CBM dump), 18 / 14 / 20 mm x 140 mm (skeleton), 16 / 10 / 18 mm (U-shape mining), 10 / 8 / 10 mm (container flatbed).
- A July 2026 mining order to Uzbekistan used T700 for both the dump box and the main beams.
- Mining duty is measured in cycles, not kilometres, so those builds are specified around impact tolerance.
- The sequence is: fix the struck volume first, then size the steel grade around it.
Related: axle brand versus axle rating, suspension types compared, and what moves the price.
