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Difficulty: MediumTyre Safety and Requirements

While inspecting your vehicle's tyres, you observe that the tread surface has worn down flush with the tread wear indicator (TWI) bars located within the primary grooves. What does this condition indicate?

  1. A
    The tyre tread depth is approximately 2.5 mm, which is well above the legal limit.
  2. The tyre has reached the legal minimum tread depth of 1.6 mm and must be replaced.Answer
  3. C
    The tyre has been operated with excessive air pressure and only requires pressure deflation.
  4. D
    The tyre has worn down to 1.0 mm and is only legal for daytime local driving.

Answer

The tyre has reached the legal minimum tread depth of 1.6 mm and must be replaced.
Tread wear indicators (TWIs) are small raised blocks moulded at exactly 1.6 mm within the main tread grooves. When the outer tread surface wears down until it is flush with these indicators, it confirms that the tyre has reached the UK legal minimum tread depth of 1.6 mm and must be replaced immediately.

Step-by-Step Solution

1
Identify the purpose and specification of tyre wear indicator (TWI) bars.
Tread wear indicators are raised ribs moulded into the bottom of the main tread grooves at exactly 1.6 mm in height.
They provide a direct visual reference to show when the tyre tread has worn down to the legal limit.
2
Assess the legal implications under UK road traffic law.
When the tread surface becomes flush with the TWI bars, the tyre has reached the statutory minimum limit of 1.6 mm across the central three-quarters.
Cars and light commercial vehicles must maintain at least 1.6 mm of tread depth throughout a continuous band across the central three-quarters of the tyre width and around its entire outer circumference.
3
Determine the required safety and maintenance action.
The tyre must be replaced immediately.
Driving on tyres at or below the legal minimum depth increases the risk of aquaplaning, severely lengthens stopping distances on wet roads, and carries legal penalties.

Key Concept

Tyre Wear Indicators and Statutory Minimum Tread Depth
Estimated Time:45s
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Topics

Tyre Safety and Requirements

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