The operation of vehicles is prohibited if:

Explanation

In both cases — both the loss of sealing in the crankcase ventilation system and fitting studded and non-studded tyres on the same axle.

Combining a studded and a non-studded tyre on one axle is the most dangerous form of mismatch, because the difference in grip between the two sides reaches its maximum in icy conditions. On ice, the studded tyre claws at the surface with its studs while the ordinary one slides almost without friction. The result of this asymmetry under braking is a turning torque: the vehicle rotates about its vertical axis, and if that axis is the rear one, the rear end comes round and control is effectively lost — all on a surface that gives no chance of correction at all.

The other item is the sealing of the crankcase ventilation system, which appears in the engine section of the list. This system must return blow-by gases from the crankcase to the intake under control; when the sealing fails, oil vapour and toxic gases are released and some of them enter the cabin through the ventilation ducts. A driver breathing that air for hours reacts more slowly.

The practical rule with which you can answer every tyre question in this chapter: on one axle, everything identical — size, tread pattern, construction, new or retreaded, studded or ordinary. And since both items in this question are on the list of defects, the comprehensive answer is correct.

• This item is a defect but not the complete answer; you have overlooked the combination of a studded and an ordinary tyre on one axle. • This is independently prohibiting too, but choosing it alone means disregarding the crankcase ventilation system leak, which appears in the engine section of the list.

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