A driver ignores the tyre-pressure warning lamp for weeks. Besides uneven tread wear, what is the most significant safety consequence of running tyres significantly underinflated?

Why B is correct

An underinflated tyre flexes far more than it was designed to. The sidewall bends repeatedly through every rotation, the internal structure heats up, and heat is what kills tyres — the failure mode is a sudden blowout at speed, the exact scenario where a blowout is most dangerous. Underinflation also changes the contact patch, dulling steering response and stretching wet stopping distances. The warning lamp is not nagging about fuel economy; it is reporting that a component carrying the whole vehicle is operating outside its thermal design envelope.

Why the other options are wrong

A. The ride becomes softer, which improves wet-weather grip

A softer ride is the sensation of a tyre working badly, and the grip that matters — especially wet braking — gets worse, not better, as the contact patch deforms and the tread pattern closes up.

C. The speedometer reads higher than the true speed

Speedometers are calibrated to the vehicle, and small tyre-diameter changes from pressure are a fraction of a percent. Whatever the gauge does, it does nothing to offset the thermal and handling damage being done.

D. Fuel consumption drops because the engine works less

Underinflation increases rolling resistance, which raises fuel consumption. The direction of the effect is the opposite of the driver's hope, and it is the least of the problems anyway.

On the road

A hatchback commutes all autumn on a rear tyre twenty percent low, the amber lamp ignored since August. On the first hard freeway run in cold November air, the overworked sidewall lets go at 70 — a bang, a violent pull, a shoulder stop on the shoulder. The repair bill for the tyre is trivial; the near-miss with the barrier is what the lamp had been arguing about for two months.

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