The operation of vehicles is prohibited if:

Explanation

In both cases; both cracks on the tyre or the rim and a change in the shape and size of the rim's bolt holes.

The wheel is the only assembly that simultaneously carries the vehicle's weight, the braking force and the lateral force of cornering, and it has no back-up system at all. That is why any visible crack on a tyre or rim, regardless of its size, prohibits operation.

A crack in metal grows. Every revolution is a fresh loading cycle, and a crack of a few millimetres reaches complete failure after a few hundred kilometres. The moment of failure is usually the worst possible one: hard braking or a bend at speed, that is, where the force on the rim is greatest. The result is a sudden loss of air and the vehicle pulling to one side while the other wheels are still gripping.

The bolt holes are just as sensitive. If their shape or size has changed and they have gone oval, the nuts no longer clamp the rim properly against the hub; the wheel develops play in its seat, the bolts fatigue and shear one after another, and finally the wheel separates from the vehicle. This fault usually warns of itself with a knocking sound in bends, and that warning is most often ignored.

Worth memorising: when inspecting a wheel, the rim matters as much as the tyre itself. Any option that reduces wheel soundness to the tyre alone has left out half the story.

• A crack on a tyre or rim is a prohibiting defect on its own, but an option that states only this has omitted the second item and is not the complete answer. • A change in the shape of the rim's bolt holes independently prohibits operation too; choosing only this item means disregarding the cracks.

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