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Difficulty: MediumEnvironmental Impact and Fuel Efficiency

A driver is inspecting their vehicle to ensure it operates with maximum fuel efficiency. Why does driving on under-inflated tyres increase fuel consumption?

  1. A
    It reduces vehicle weight and causes the wheels to spin with less grip
  2. It increases the tyres' rolling resistance against the road surfaceAnswer
  3. C
    It causes the vehicle to coast automatically between gear changes
  4. D
    It only increases fuel usage if tyre tread depth is below the legal limit of 1.6 mm

Answer

Driving on under-inflated tyres increases fuel consumption because it increases rolling resistance against the road surface.
Correctly inflated tyres maintain their designed shape and minimal rolling resistance. When tyres are under-inflated, they flex excessively and drag across the road surface, increasing rolling resistance. The engine must expend extra energy and consume more fuel to propel the vehicle forward.

Step-by-Step Solution

1
Examine how tyre pressure affects the physical profile of the tyre.
Under-inflated tyres sag and deform under the vehicle's weight, increasing the contact area and tyre sidewall flex.
Correct inflation pressure is necessary to maintain the optimal structural rigidity and contact patch of the tyre.
2
Determine the mechanical impact of this deformation on vehicle movement.
The enlarged contact area and increased friction generate greater rolling resistance as the wheels turn.
Rolling resistance opposes forward motion and must be overcome continuously by engine power.
3
Connect increased rolling resistance to engine energy demand and fuel usage.
The engine must burn more fuel to maintain any given cruising speed, producing higher exhaust emissions.
Overcoming unnecessary resistance requires greater torque and sustained throttle input.

Key Concept

Under-inflated tyres increase rolling resistance, requiring the engine to consume more fuel to maintain road speed.
Estimated Time:45s
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Topics

Environmental Impact and Fuel Efficiency

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