As a rule, the larger the caravan, the greater the effects of cross-winds on trailer stability, but this doesn’ t mean your small single-axle van is immune to the wobbles.
Pig trailers have the axles and wheels somewhere in the middle of the trailer, making steering and reversing easy and not requiring any special mechanism. This is why they are so popular and perfect for light vehicles to tow. But they have an inherent instability caused by the weight of the overhanging front and rear of the trailer. Fortunately, caravan manufacturers are aware of this and design their caravans to minimise the instability.
The unfortunate owner of this rig told police he had never experienced any instability until he came down this section of road. Steep downhill roads can unmask hidden instability.
WHAT CAUSES THE WOBBLES?
Before we get too far into the causes of the wobbles, it’ s important to understand exactly what they are. The wobbles are a form of oscillation called‘ mechanical resonance’. If you want to send yourself to sleep, you can Google it, but to put it into simple terms, mechanical resonance is the tendency of mechanical systems to respond with greater force when the frequency of their movement matches the system’ s natural frequency of vibration. This can lead to violent swaying motions that often result in catastrophic failure.
You might have seen a famous example of this in a film of the Tacoma Narrows Bridge in the US, where the wind blowing against the side of the bridge caused it to swing and twist rhythmically. When the bridge experienced strong, sustained winds, the everincreasing swaying eventually led to the bridge tearing itself apart and collapsing.
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