The operation of vehicles is prohibited if:

Explanation

If the residual tread depth of the passenger car trailer's tyres is less than 1.6 mm.

A trailer towed behind a passenger car is subject, as regards tyres, to the same limit as the towing vehicle: a minimum residual tread depth of 1.6 mm. Below that figure, operation of the combination is prohibited — even if the car's own tyres are new.

Tread has a simple but vital job: it channels water out from beneath the tyre so that contact with the asphalt is preserved. With tread below the permitted limit, the tyre slides on a film of water (aquaplaning) and grip drops sharply. On a trailer this phenomenon is even more dangerous: when the rear wheels of the combination lose grip, the trailer starts to sway laterally and can drag the whole outfit into jack-knifing and rollover — something the driver has almost no ability to control.

Worth memorising, and often forgotten by drivers: a trailer's tyres cover few kilometres but stand for years in the sun and unused; their deterioration is more a matter of rubber ageing than of wear. Before every trip, check the trailer's tread and pressure separately from the car's. By contrast, an amber indicator at the rear is exactly the standard colour and is no offence.

• Indicators at the rear must also be yellow/amber; this option describes the vehicle's correct condition and has no place on the list of defects. • Since the second item is not a defect, the "in both cases" option is ruled out too.

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