How to measure tyre tread depth

Much confusion exists regarding the correct manner in which to measure tyre tread depth. This is, however, prescriptively described by South African law.

Although some sections of the law are somewhat ambiguous when read in isolation, when one considers all the normative references in the National Road Traffic Act and the applicable standards – such as the SABS 1550 and SABS 047 – one is able to understand the correct procedure.

The following documentation relates to the legal requirements concerning the tread depth of a tyre.

National Road Traffic Act and Regulations and other references:

Regulation 212 of the National Road Traffic Act, Act 93 of 1996 states the following:

212. No person shall operate on a public road –
213. a motor vehicle –

1. which is fitted with a pneumatic tyre unless such tyre displays throughout, across its breadth and around its entire circumference, a pattern which is clearly visible, and has a tread of at least one millimetre in depth; or
2. which is fitted with a pneumatic tyre which contains a tyre tread depth indicator, if the tread is level with the tyre tread depth indicator.

It should be noted that Regulation 212 (j) (i) is applicable where the tread depth is specified as at least 1 mm. Subsection (j)(ii) relates to industrial tyres with no tread pattern. The tread depth indicator differs from the “tread wear indicator” (TWI). The tread wear indicator is used on passenger tyres and is present inside the main grooves (where the tread depth is measured). It indicates that approximately 1,6 mm of tread is still present when worn to the level of the TWI.

Regulation 129 states:

129. The requirements for registration of a testing station, are –

• the level of technical competence required in code of practice SABS 0216 “Vehicle test station evaluation”; and
• the manner of examination and testing of a motor vehicle at the testing station as required in code of practice SABS 047 “The testing of motor vehicles for roadworthiness”.

The normative references included in SABS 047 include but are not limited to SABS 1550-2,
SABS 1550-3, and SABS 1550-6. These form part of SABS 1550-1 to 7: “Motor vehicle tyres and rims – Dimensions and loads”, which further refers to ARP 007 in the following manner. “Information on the care, maintenance and use of motor vehicle tyres and rims is contained in ARP 007.”

This means that the following documents are all used for determining the condition of tyres in terms of roadworthiness:

• The National Road Traffic Act, Act 93 of 1996
• The National Road Traffic Regulations, 1999
• SABS 0216: Vehicle test station evaluation
• SABS 047: The testing of motor vehicles for road worthiness
• The Vehicle Examiners Handbook, which contains guidelines for the vehicle examiner concerning the requirements of SABS 047
• SABS 1550: Vehicle tyres and rims: dimensions and loads
• ARP 007: The care, maintenance and use of motor vehicle tyres and rims

The tread of a tyre must therefore be measured in the main grooves of the tyre and in other areas where the tread wear indicators indicate that the tread depth should be measured, as prescribed in ARP 007: 1992, “The care, maintenance and use of motor vehicle tyres and rims”, reaffirmed on 30 July 2002.

Paragraph 3.3.1.3 states: “It is recommended that no vehicle be operated with tyres that do not have a minimum tread pattern depth of 1.0 mm in all the main grooves across the full width of their tread contact area and around the full tyre circumference, with the exclusion of areas where tread-wear indicators or tiebars (or both) exist.”

Article by Du Métier Technical Investigations and Consultants, a company formed to assist members of the legal profession (or private clients involved in motor vehicle collisions) in the understanding of technical and engineering related matters.

See www.dumetier.com/ for further information.