Ski coach: total weight and rear-axle overload
An 18,000 kg coach is loaded for a ski day trip. Kerb weight is 13,400 kg, split 4,900 kg front axle and 8,500 kg rear axle; plated axle limits are 7,500 kg front and 11,500 kg rear. There are 46 adult passengers averaging 80 kg plus 8 kg hand luggage each. The rear luggage hold contains 1,200 kg of skis and boots; a roof box carries 90 kg. Seating is 10 passengers in the front third, 20 in the middle and 16 at the rear. The middle-row load can be assumed to split 50/50 between axles; rear hold and roof load act on the rear axle. The coach has no front luggage hold. The tour guide wants to leave immediately because the pass closes at 10:00, and the driver has a 30-minute window to adjust the load.
1. Calculate the total weight and the front and rear axle loads. Identify every legal problem.
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Passenger load: 46 × 80 kg = 3,680 kg. Hand luggage: 46 × 8 kg = 368 kg. Rear hold: 1,200 kg. Roof box: 90 kg. Total payload = 3,680 + 368 + 1,200 + 90 = 5,338 kg. Total weight = 13,400 + 5,338 = 18,738 kg, which exceeds the 18,000 kg plated maximum by 738 kg.
For axle loads, use 80 kg + 8 kg = 88 kg per passenger. Front third: 10 × 88 = 880 kg to the front axle. Rear third: 16 × 88 = 1,408 kg to the rear axle. Middle 20 × 88 = 1,760 kg, split 880 kg front and 880 kg rear. Rear hold and roof act on the rear axle: 1,200 + 90 = 1,290 kg.
Front axle = 4,900 + 880 + 880 = 6,660 kg, below 7,500 kg by 840 kg. Rear axle = 8,500 + 1,408 + 880 + 1,290 = 12,078 kg, above 11,500 kg by 578 kg. The coach is therefore overloaded both in total and on the rear axle, even though the front axle has margin. It must not leave as loaded.
2. Propose a load plan that brings the coach within total and axle limits without splitting the passenger group.
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Because there is no front luggage hold, moving load forward is not a quick option. The total must fall by at least 738 kg, and the rear axle by at least 578 kg. Removing the roof box saves 90 kg from the rear axle and from the total. Removing 650 kg from the rear luggage hold saves another 650 kg from the rear axle. New total = 18,738 − 90 − 650 = 17,998 kg. New rear axle = 12,078 − 90 − 650 = 11,338 kg. New front axle stays at 6,660 kg. Both axles and the total are now within limits, and all 46 passengers remain aboard.
The remaining 550 kg in the rear hold must be secured against movement, and the load must be rechecked after any transfer. The guide should be told that the roof box and 650 kg of luggage cannot travel on this coach; a second vehicle or freight transfer is needed. The driver should not accept a plan that merely moves luggage around inside the rear without reducing the rear-axle load or total weight.
3. Why does the roof load matter beyond the axle-load calculation?
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A roof box raises the centre of gravity. Even if the axles were within their plated limits, a high load increases body roll on bends, reduces stability in crosswinds and on wet or snowy roads, and can worsen the outcome of an emergency swerve. The roof itself also has a load limit and fixing points that must be respected. On a ski trip the roof load may be combined with winter tyres, snow and passengers moving around, so stability margins are already lower. The driver should therefore remove or reduce the roof load first, check the roof limit, and explain to the guide that legal axle limits are only one part of safe loading.