How to Load a Caravan Safely

The above shows the effective mass of locating a 20 kg item at various distances from the axle/s of a caravan.

This article (and principle) shows the importance of where mass is located along the length of a caravan.

As with a playground see-saw, two children of the same mass sitting at equal distances from the central pivot balance each other. Likewise an adult sitting near the middle on the one side can balance the far less mass of a child at its far end.

A centre-axled caravan behaves in a similar way - it is (in effect) a see-saw on wheels. Where you located stuff along its length has exactly the same effect - that its distance from the axle increases its 'effective weight'. (In physics, the effect of such length is called a 'moment arm'.

 A single axle trailer (or twin axles located close together) behaves like the see-saw's ends pitching up and down, with the axle being the pivot. It is more complex though - the caravan also yaws (sways) sideways under tow as well as up and down.

With that sideways movement too, a tool box weighing 20 kg directly above a 6 metre long caravan/s axle) tool box behaves like a 20 kg tool box: i.e. it has next to no effect. But if we move that tool box half-way toward the back of the caravan and it then sways, that tool box has an effective mass of 40 kg - because it is further away from the pivot.  

The further from the axle/s the greater the effect. If you carry that tool box on a 10 kg external rack at the rear of the trailer, the tool box will have an effective mass of around 80 kg and the rack an effective mass of around 40 kg.

The tool box and rack in effect becomes four times heavier at the back of a 7 metre trailer compared to in the middle and exerts such additional force when the trailer pitches and yaws (sways).

The effect is similar at the front of a trailer, although the potential for pitching and yawing here is to some extent reduced by the reluctance of the tow vehicle to be moved sideways, and by the rear tyres of the tow vehicle.

It is never a good idea to store heavy items, particularly tool boxes, spare wheels and full jerry cans at the very front or rear of a trailer.

Load all small heavy items in the tow vehicle (if loading legal permits) or as close to the caravan's axle/s as possible. 

The caravan needs to be about 10% nose heavy, but that is best done by moving heavy stuff just ahead of the axles - not like weight lifters barbell (that has all virtually all the weight at the ends).

It also shows why RV Book's publications so strongly condemn locating heavy spare wheels etc at the extreme rear of long caravans.

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