You are driving an unladen 44-tonne artic on a motorway in strong crosswinds. You notice the empty trailer is yawing slightly. Compared to a fully laden trailer, what makes the unladen trailer MORE susceptible to yaw instability?
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ALower mass reduces tyre cornering stiffness relative to aerodynamic side forces, making yaw harder to resist
BThe coupling friction between fifth wheel and king pin is greater when unladen, amplifying oscillation
CEmpty trailers have higher centres of gravity because the floor flexes upward when unloaded
DUnladen trailers run on over-inflated tyres which reduce contact patch and cause instability
✓ Correct answer: A. Lower mass reduces tyre cornering stiffness relative to aerodynamic side forces, making yaw harder to resistWith low mass, the inertial resistance to lateral movement is reduced; aerodynamic side forces (which are mainly a function of body area, not mass) therefore represent a much higher proportion of the total restoring force, making yaw oscillation more likely in high winds.
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