Pre-Trip Decision on an Overloaded Rice Truck at Battambang
You are about to leave a depot near Battambang with a two-axle rigid truck. The plate in the cab states gross vehicle weight 16,000 kg; the truck's tare weight is 6,200 kg. The load is 420 sacks of rice at 25 kg each, stacked 2.6 m high, with the top four rows standing above the 1.9 m side rails. No straps are fitted yet, and the rear of the stack overhangs the bed by 0.8 m. The air system takes 4 minutes to build from zero to 6 bar. The offside inner rear tyre reads 90 psi against a specification of 110 psi, and the other tyres are at 110 psi. It is 05:30; the 190 km run to Poipet should take about four hours; the first 20 km is dusty laterite road and rain is forecast for the afternoon.
1. Calculate the load situation and state exactly what must change before the truck moves.
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Weight check:
- Load = 420 sacks × 25 kg = 10,500 kg
- Tare 6,200 kg + load 10,500 kg = 16,700 kg
- Plate limit = 16,000 kg, so the truck is 700 kg over its gross vehicle weight - about 28 sacks too many.
Overloading is not a paperwork problem. It overloads both axles, lengthens the stopping distance, overheats tyres on a four-hour run in forecast rain, and makes the truck squat so the steering feels light and the headlights point up.
Action: remove at least 28 sacks (take 30 for margin), or move them to a second vehicle. Then confirm the front and rear axle loads are both within their plated limits, not just the total - a load stacked too far back can overload the rear axle even when the total is legal.
The 0.8 m rear overhang must be marked so following traffic can see the projection, and the tailgate or rack must actually retain the rear of the stack.
2. Two defects are listed. Which one stops the trip, and how do you reason about the other?
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The slow air build-up stops the trip until diagnosed. A healthy system normally reaches working pressure in a fraction of the time this one takes; four minutes to reach only 6 bar points to a compressor or governor fault, a leaking line, or a stuck unloader valve. The practical test is this: with a loaded truck you need full pressure plus reserve for repeated brake applications. If the system cannot build pressure quickly, it also may not recover pressure during a long descent or heavy traffic. That is a brake-failure risk, not an inconvenience.
The under-inflated inner dual (90 psi vs 110 psi) must be corrected before departure, though it is fixable on the spot. A soft inner tyre in a dual pair carries less than its share of the load, so the outer tyre is overloaded, the two tyres scrub against each other, and the pair runs hot. On a 190 km run in afternoon heat this is a classic dual blowout, and a rear blowout on a loaded two-axle truck is hard to control.
Inflate it, check for a slow leak or a damaged valve, and re-check after the first hour.
3. Describe how you would secure and prepare the rice stack for the run.
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The load has three problems - height, no restraint, and a rear overhang.
- Reduce and re-stack. After removing the excess sacks, rebuild the stack so it is interlocked and level, with the heaviest rows low and the load pushed forward against the headboard and evenly spread over the bed.
- Restrain it properly. Side rails alone do not restrain a 2.6 m stack; they only contain it. Fit rated straps or ropes across the load at close intervals, each tensioned down onto the stack, and cross-lash the top rows so they cannot slide forward under braking. The restraint must be able to hold the load against heavy braking, not merely hold a tarpaulin down.
- Deal with the overhang. Keep it as short as possible, mark it so it is visible to traffic behind, and make sure the rear of the stack cannot slide backwards.
- Height and centre of gravity. A high, loose stack raises the centre of gravity and shifts it in corners. On wet laterite and then wet tarmac, that is the difference between a corner and a rollover.
- Cover it with a tarpaulin tied down, so rain does not add weight and the bags do not shed rice onto the road.