Load shift on a light trailer before a mountain pass
You are about to tow a braked single-axle trailer with a passenger car. The car's registration document gives a maximum towing mass of 1,300 kg for a braked trailer, and the trailer's own plate gives a maximum technically permissible mass of 1,500 kg. You have loaded the trailer with 900 kg of bagged sand and placed the bags mostly behind the axle to make unloading easier at the site. The tow ball is fitted, the coupling is locked, and the breakaway cable is attached. The trailer's jockey wheel is raised. You are heading for a mountain pass with long descents. The trailer tyres look slightly under-inflated and one has a cut in the sidewall that does not show cords.
1. Assess the mass combination and state what must change before departure.
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Two separate limits apply and the lower one governs. The car may tow at most 1,300 kg with a braked trailer; the trailer's own plate allows 1,500 kg, but that does not raise the car's limit. The actual combination is 900 kg of load plus the trailer's unladen mass, which is unknown from the setup - so the first step is to weigh the trailer (or read its unladen mass from the plate) and confirm the total stays at or below 1,300 kg. If the trailer weighs, say, 400 kg unladen, the combination is 1,300 kg and is right at the limit, leaving no margin. Also check the car's gross train mass and its rear-axle load with the trailer coupled; exceeding either is an offence even if the towed mass looks legal. If the total exceeds 1,300 kg, remove sand before departure.
2. Explain the danger of the load position and how to correct it.
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Loading the bags behind the axle creates a negative or very small drawbar load and makes the trailer prone to snaking (yaw oscillation) at speed, especially on descents. A single-axle trailer needs a positive nose weight - typically around 4–7% of the trailer mass, within the car manufacturer's permitted tow-ball load. Correct it by moving the bags forward of the axle, spreading them low and centred, then re-checking the nose weight with a gauge or a bathroom scale under the coupling. Secure the load against fore-aft and lateral movement with straps to the trailer's lashing points, not to the bag handles. After loading, re-check tyre pressures and the coupling lock, and confirm the breakaway cable is routed so it cannot drag or snag.
3. The trailer tyre has a sidewall cut and looks under-inflated. What is the correct decision, and what changes on the descent?
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Do not depart on that tyre. A sidewall cut is a structural defect: sidewalls flex constantly and cannot be repaired safely, and under-inflation makes the flexing and heat far worse, with a real risk of blow-out at speed or under braking. Fit the spare or have the tyre replaced, and set pressures to the trailer manufacturer's figure for the actual load. On the mountain descent: select a lower gear before the slope begins and use engine braking to hold speed, braking in short firm applications rather than riding the brakes, which can fade or boil the fluid. Keep the speed low enough that the trailer never starts to snake; if it does, ease off the accelerator gradually and do not brake hard or steer sharply - that amplifies the oscillation. Leave a longer gap and avoid overtaking on descents.